Transition between realities

Abstract

An apparatus 10 comprises control means 12 for controlling the presentation of content by a rendering device 20 to a user 2. The control means provides spatially-dependent variation of transfer of rea

Description

Reference is made to three different realities: real-world reality, virtual reality, and mixed reality (also called augmented reality). Real-world reality is what we can see perceive around us. In augmented or mixed reality, real-world content is transferred to a user and mixed with virtual content. For example, a see-through display displays virtual objects that augment or mix with the real-world content visible through the see-through display. For example, a no-see-through display displays virtual objects that augment or mix with the real-world content captured by one or more cameras and displayed on the display. In virtual reality, no real-world content is transferred via the rendering device to a user and the user experiences only rendered virtual content. For example, a no-see-through display displays virtual content. Virtual reality is immersive. It is desirable not to remove a user from the immersive experience unless necessary. However, it is also desirable to remove a user from the immersive experience and bring them back to the real-world when necessary. BRIEF SUMMARY According to various, but not necessarily all, examples there is provided an apparatus comprising: control means for controlling presentation of content by a rendering device to a user, wherein the control means is configured to: provide spatially-selective variation of a transfer of real-world content by the rendering device to the user; and cause provision of a spatially-selective rendering of virtual content by the rendering device to the user. In some, but not necessarily all examples, the apparatus is configured to provide control signals to the rendering device, wherein the control signals are: configured to control a visual transparency of a head-mounted display to provide a spatially-selective variation of visual transparency of the display which provides a spatially-selective variation of a transfer of real-world visual content to the user; and / or configured to provide control signals to the rendering device, wherein the control signals are configured to control spatial rendering of audio sources to provide a spatially-selective variation of audio transparency to the real-world space which provides a spatially-selective variation of a transfer of real-world audio content to the user. In some, but not necessarily all examples, the apparatus comprises: means for controlling simultaneously variation of: spatially-selective transfer of real-world content by the rendering device to the user; and spatially-selective rendering of virtual content by the rendering device to the user. In some, but not necessarily all examples, the control means comprises: means for increasing transfer of real-world content associated with a first portion of a scene and for increasing transfer of real-world content associated with a second portion of the scene, configured to increase the transfer of real-world content associated with the first portion of the scene more than the transfer of real-world content associated with the second portion of the scene which provides spatially-selective variation of transfer of real-world content by the rendering device to the user. In some, but not necessarily all examples, the control means comprises adapting means for adapting virtual content to decrease an intensity of rendering the virtual content associated with a third portion of the scene more than an intensity of rendering the virtual content associated with a fourth portion of the scene. In some, but not necessarily all examples, the adapting means is configured to decrease an intensity of rendering the virtual content associated with the third portion of the scene more than an intensity of rendering the virtual content associated with the fourth portion of the scene while maintaining the association of the virtual content with the same portions of scene. In some, but not necessarily all examples, the apparatus comprises: fading means for fading-in spatially selective real-world content associated with one or more fade-in portions of a scene while simultaneously fading-out spatially-selective virtual content associated with one or more fade-out portions of the scene. In some, but not necessarily all examples, the one or more fade-in portions of the scene have a combined area that is smaller than a combined area of the one or more fade-out portions of the scene. In some, but not necessarily all examples, the fading means is configured to fade-in at different fade-in rates at different ones of the one or more fade-in portions of the scene and / or fade-out at different fade-out rates at different ones of the one or more fade-out portions of the scene. In some, but not necessarily all examples, the fading means is configured to fade-in at a faster rate at a portion of the scene limited to a real-world visual object or real-world audio source. In some, but not necessarily all examples, the apparatus comprises: means for classifying real-world visual objects and / or real-world audio sources to select one or more real-world visual objects and / or one or more real-world audio sources; and means for fading-in real-world content at a portion of the scene limited to the selected one or more real-world visual objects and / or one or more real-world audio sources. In some, but not necessarily all examples, the apparatus comprises: means for ranking the classified real-world visual objects and / or classified real-world audio sources to select a limited number of the ranked real-world visual objects and / or real-world audio sources. In some, but not necessarily all examples, the apparatus comprises: means for enabling user control of at least one of: classifying, ranking, the limited number of the ranked real-world visual objects and / or real-world audio sources, a fading-in rate. In some, but not necessarily all examples, the fading means is configured to fade-out at a slower rate at a portion of the scene limited to a virtual visual object or virtual audio source compared to a portion of the scene not limited to the virtual visual object or the virtual audio source. In some, but not necessarily all examples, the apparatus comprises: means for classifying virtual objects and / or virtual audio sources in the virtual content to select one or more virtual visual objects and / or one or more virtual audio sources; and means for fading-out virtual content at a portion of the scene not limited to the selected one or more real-world visual objects and / or audio sources. In some, but not necessarily all examples, the apparatus comprises: means for ranking the classified virtual visual objects and / or virtual audio sources to select a limited number of the ranked virtual visual objects and / or virtual audio sources. In some, but not necessarily all examples, the apparatus comprises: means for enabling user control of at least one of: classifying virtual objects and / or virtual audio sources , ranking classified virtual visual objects and / or virtual audio sources, the limited number of the ranked virtual visual objects and / or virtual audio sources, a fade-out rate. According to various, but not necessarily all, examples there is provided a system comprising the apparatus as claimed in any preceding claim and the rendering device, wherein the rendering device comprises a head-mounted display configured to visually isolate a user’s eyes, from an external real-world space external to the rendering device, in an internal space wherein a display provides an interface between the internal space and the external real-world space and wherein a visual transparency of the display is controllable to provide a spatially-selective variation of visual transparency to the external real-world space which provides spatially-selective variation of the transfer of external real-world visual content to the user; and / or wherein the rendering device comprises a head-mounted spatial audio system configured to audibly isolate a user’s ears, from an external real-world space external to the rendering device, in an internal space wherein one or more spatial audio channels provide an interface between the internal space and the external real-world space and wherein a spatial rendering of external audio sources is controllable to provide a spatially-selective variation of audio transparency to the external real-world space which provides spatially-selective variation of the transfer of external real-world audio content to the user. According to various, but not necessarily all, examples there is provided a method comprising: controlling spatially-selective variation of a transfer of real-world content by a rendering device to a user; and controlling spatially-selective rendering of virtual content by the rendering device to the user. According to various, but not necessarily all, examples there is provided a computer program that, when run on a computer, performs: controlling spatially-selective variation of a transfer of real-world content by a rendering device to a user; and controlling spatially-selective rendering of virtual content by the rendering device to the user. According to various, but not necessarily all, examples there is provided examples as claimed in the appended claims. While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all of the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all of the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. BRIEF DESCRIPTION Some examples will now be described with reference to the accompanying drawings in which: FIG 1 illustrates an example of an apparatus 10 for controlling presentation of content by a rendering device 20 to a user 2; FIGs 2A, 2B, 2C illustrate an example of a rendering device 20 variably transferring external real-world content 32 from the real-world 30 to a user FIG 2D illustrates spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2; FIGs 2E, 2F, 2G illustrate an example of a rendering device 20 providing a selective rendering of virtual content 42 to the user 2; FIG 2H illustrates spatially-selective rendering of virtual content 42; FIGs 3A and 3B illustrate examples of content 70; FIGs 4A, 4B, 4C, 4D illustrate an example of a rendering device 20. FIG 5A illustrates virtual content 42; FIG 5B illustrates classification of virtual objects 48 into different subsets 48_1,48_2; FIG 5C illustrates rendering the virtual content 42 with spatial variation as spatially-varying, rendered virtual content 46; FIG 6A illustrates the real-world content 32; FIG 6B illustrates classification of objects 38 into different subsets 38_1, 38_2; FIG 6C illustrates transfer of the real-world content 32 with spatial variation as spatially-varying, transferred external real-world content 36; FIG 7 illustrates that the rendering device 20 is configured to simultaneously provide, in overlap, the user virtual scene 50 of FIG 5C and the user real scene 52 of FIG 6C as a combined scene 54; FIGs 8A to 8E illustrate a user virtual scene 50 during an evolving time sequence. FIGs 9A to 9E illustrate a user real scene 52 during the evolving time sequence; FIGs 10A to 10E illustrate the user virtual scene 50 and the user real scene 52 in overlap as presented combined scene 54; FIGs 11A-11C, 12A-12C and 13 illustrate different fade-in for different real-life content / objects 38; FIGs 14A-14E, 15A-15E, 16A-16E illustrate of the user virtual scene 50, the user real scene 52 and the combined scene 54 and different fade-in rates for different real-life content / objects 38; FIG 17 illustrates an example of a method 500; Fig 18 illustrates an example of a controller 400; Fig 19 illustrates an example of a computer program 406. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DETAILED DESCRIPTION The following description relates to examples of an apparatus 10 comprising: control means 12 for controlling presentation of content 70 by a rendering device 20 to a user 2, wherein the control means 12 is configured to: provide spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2; and cause provision of a spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. In some examples, the spatially-selective variation of the transfer of external real-world content 32 by the rendering device 20 to the user 2 occurs via spatially-selective variation of transparency of a see-through display. In some examples, the spatially-selective variation of the transfer of external real-world content 32 by the rendering device 20 to the user 2 occurs via spatially-selective variation of display of real-world content captured by one or more cameras. FIG 1 illustrates an example of an apparatus 10 comprising control means 12 for controlling presentation of content by a rendering device 20 to a user 2. The control means 12 is configured to provide spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2. The control means 12 is configured to cause provision of a spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. In this example, the control means 12 produces control signals 14 configured to: provide spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2; and cause provision of a spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. The control means 12 produces control signals 14_1 configured to provide spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2. The control means 12 produces control signals 14_2 configured to provide a spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. In some examples, the apparatus 10 comprises the rendering device 20 or vice verse. In some examples, the apparatus 10 is distinct from but in communication with the rendering device 20. In some examples, the apparatus 10 is configured for virtual reality rendering. It may also be configured for augmented reality and / or mixed reality. The apparatus 10 is configured for virtual reality rendering and for gradually switching between different realities, such as from virtual reality to augmented reality and vice versa. In some examples, the apparatus 10 is configured for virtual reality rendering using a no-see-through mode and for gradually switching between different realities, such as from no-see-through virtual reality to augmented reality using a see-through view and vice versa. FIGs 2A, 2B, 2C illustrate an example of a rendering device 20. The rendering device 20 variably transfers external real-world content 32 from the real-world 30 to a user (not illustrated). The transferred external real-world content 34 has different intensities in FIGs 2A, 2B , 2C. In FIG 2A 0% is transferred, in FIG 2B 50% is transferred and in FIG 2C 100% is transferred. FIG 2D illustrates how the rendering device 20 is controlled, via control signals 14_1 (not illustrated) to present content to the user 2, to provide a spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2. The rendering device 20 has spatially distinct portions 22. A first subset 22_1 of the portions 22 is controlled, via control signals 14_1 (not illustrated), to operate as illustrated in FIG 2A. There is no transferred external real-world content 34. There is 0% transfer of the external real-world content 32 through the first subset 22_1 of the portions 22. A second subset 22_2 of the portions 22 is controlled, via control signals 14_1 (not illustrated), to operate as illustrated in FIG 2B. The transferred external real-world content 34 is a lower intensity version of the external real-world content 32. There is 50% transfer of the external real-world content 32 through the second subset 22_2 of the portions 22. A third subset 22_3 of the portions 22 is controlled, via control signals 14_1 (not illustrated), to operate as illustrated in FIG 2C. The transferred external real-world content 34 is substantially the same as the external real-world content 32 . There is 100% transfer of the external real-world content 32 through the second subset 22_2 of the portions 22. It should be understood that the % transfer values used are only illustrative and other % transfer values can be used. The rendering device 20 is controlled to have a transfer of content that varies with location of the content (spatially varies). This is spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2. The collection of the transferred external real-world content 34, which varies spatially, is labelled as spatially-varying, transferred external real-world content 36. FIGs 2E, 2F, 2G illustrate an example of a rendering device 20. This can, for example, be the rendering device 20 as previously described. The rendering device 20 provides a selective rendering, to the user 2 (not illustrated), of virtual content 42. The rendered virtual content 44, determined from original virtual content 42, has different intensities compared to the original virtual content 42 in FIGs 2A, 2B , 2C . In FIG 2A no virtual content 44 is rendered, in FIG 2B rendered virtual content 44 is rendered at 50% intensity of the original virtual content 42 and in FIG 20 rendered virtual content 44 is rendered at 100% intensity of the original virtual content 42. FIG 2H illustrates how the rendering device 20 is controlled, via control signals 14_2 (not illustrated) to present content to the user 2, to provide a spatially-selective rendering of virtual content 42 to the user 2. The rendering device 20 has spatially distinct portions 22. These can be the same or different portions 22 illustrated in Fig 2D. A first subset 22_1 of the portions 22 is controlled, via control signals 14_2 (not illustrated), to operate as illustrated in FIG 2E. There is no rendered virtual content 44 by the first subset 22_1 of the portions 22; there is no rendered virtual content provided by the first subset 22_1 of the portions 22. A second subset 22_2 of the portions 22 is controlled, via control signals 14_2 (not illustrated), to operate as illustrated in FIG 2F. The original virtual content 42, associated with the second subset 22_2 of the portions 22, is rendered via the second subset 22_2 of the portions 22 at 50% intensity of the original virtual content 42 A third subset 22_3 of the portions 22 is controlled, via control signals 14_2 (not illustrated), to operate as illustrated in FIG 2G. The original virtual content 42, associated with the third subset 22_3 of the portions 22, is rendered via the third subset 22_3 of the portions 22 at 100% intensity of the original virtual content 42. It should be understood that the % intensity values used are only illustrative and other % intensity values can be used. The rendering device 20 is controlled to provide rendered content that varies in intensity with location of the content (spatially varies). This is a spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. The collection of the rendered virtual content 44, which varies spatially, is labelled as spatially-varying, rendered virtual content 46. In at least some examples, the apparatus 10 is configured to control simultaneously varying of spatially-selective transfer of external real-world content 32 by the rendering device 20 to the user 2 and spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. The apparatus 10 controls simultaneously varying of: i) spatially-selective transfer of external real-world content 32 by the rendering device 20 to the user 2 and ii) spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. In at least some example, the rendering device 20 is configured to perform simultaneous varying of spatially-selective transfer of external real-world content 32 by the rendering device 20 to the user 2 and of spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. FIGs 3A and 3B illustrate examples of content 70. Any of the external real-world content 32, the transferred external real-world content 34, spatially-varying transferred external real-world content 36, the virtual content 42, the rendered virtual content 44 and the spatially-varying rendered virtual content 46 can comprise content 70. The content 70 can, for example, be or comprise audio content 72. The content 70 can, for example, be or comprise visual content 76. The content 70 can, for example, be or comprise audio-visual content 76 that comprises audio content 72 and visual content 76. FIG 3A illustrates an example where the content 70 comprises spatial audio content 72. The spatial audio content 72 comprises one or more sound sources 74 located at different positions. The sound sources 74_1, 74_2 are located at different three-dimensional positions in a three-dimensional audio space. When rendered, the three-dimensional audio space can be described as an audio scene. FIG 3B illustrates an example where the content 70 comprises visual content 76. The visual content 76 comprises one or more visual objects 78 located at different positions. The visual objects 78_1, 78_2 are located at different three-dimensional positions in a three-dimensional visual space. When rendered, the three-dimensional visual space can be described as a visual scene. The real-world content 32 is audio content 72 , visual content 76 or audio and visual content. The virtual content 42 is audio content 72 , visual content 76 or audio and visual content. FIGs 4A, 4B, 4C, 4D illustrate an example a rendering device 20. In this example, the rendering device 20 is a head-mounted device and comprises display-glasses 24 for the eyes of the user 2 and audio output devices 29_1, 29_2 for the ears of the user 2. Although in this example, the display-glasses 24 is integrated into a pair of glasses and is mounted directly in front of both eyes of the user 2, other types of display are possible such as direct projection displays. Although in this example, the audio output devices 29_1, 29_2 are over-ear devices, in other examples they can be for example on-ear or in-ear devices. FIG 4A is a front view. FIG 4B is a side view. FIG 4C is a sectional front view, where the cross-section illustrates an example of an interior of the audio output devices 29_1, 29_2. FIG 4D is a sectional front view, where the cross-section illustrates an example of an interior of the display-glasses 24. The display-glasses 24 comprise a display 21 and a visually isolating surround 23. The display 21 and the visually isolating surround 23 create a visually isolated internal space 25 between the eyes of the user 2 and the display 21. Each audio output device 29 comprises one or more audio transducers 26 and an audio-isolating portion 27. The audio-isolating portion 27 creates an audio- isolated internal space 28 within an ear canal of the user 2. The rendering device 20 is configured to control a visual transparency of the headmounted display 21 to provide a spatially-selective variation of visual transparency of the display 21 which provides a spatially-selective variation of a transfer of external real-world content (external real-world visual content 76) to the user 2. The rendering device 20 is configured to control spatial rendering of external audio sources to provide a spatially-selective variation of audio transparency to the external real-world 30 space which provides a spatially-selective variation of a transfer of external real-world content (external real-world audio content 72) to the user 2. The rendering device 20 is configured to simultaneously vary: i) spatially-selective transfer to the user 2 of external real-world content 32 by the display 21 and / or audio output devices 29; and ii) spatially-selective rendering to the user 2 of virtual content 42 by the display 21 and / or audio output devices 29. The head-mounted display-glasses 24 are configured to visually isolate a user’s eyes, from the external real-world 30 external to the display-glasses 24, in an internal space 25. The display 21 provides an interface between the internal space 25 and the external real-world 30. A visual transparency of the display 21 is controllable to provide a spatially-selective variation of visual transparency to the external real-world 30 which provides spatially-selective variation of the transfer of external real-world visual content 76 to the user 2. The head-mounted spatial audio system 29_1,29_2 is configured to audibly isolate a user’s ears, from the external real-world 30 external to the audio output devices 29_1, 29_2, in an internal space 28. In some examples, in addition or alternatively to spatially isolating users ears ANC (Active Noise Cancellation) is used One or more spatial audio channels provide an interface between the internal space 28 and the external real-world 30. Spatial rendering of external audio sources 74 is controllable to provide a spatially-selective variation of audio transparency to the external real-world 30 which provides spatially-selective variation of the transfer of external real-world audio content 72 to the user 2. The following examples illustrate content whether virtual content 42 or external real-world content 32 as visual content 76 for the purposes of easy illustration. However, it should be understood that although the examples illustrated are applied using visual content 76 they can also be applied, additionally or alternatively, using audio content FIG 5A illustrates virtual content 42. If the rendering device 20 renders the virtual content 42 without any fade-out then the rendered virtual content 44 is the virtual content 42 and the spatially-varying, rendered virtual content 46 is the virtual content 42. The virtual content 42 comprises different portions and can comprise different virtual objects 48. As illustrated in FIG 5B the portions / virtual objects 48 are classified 60 into different subsets 48_1, 48_2. In at least some examples, the subset 48_2 of the virtual content 42 corresponds to a contextually most important object or objects. As illustrated in FIG 5C, the rendering device 20 renders the virtual content 42 with spatial variation as spatially-varying, rendered virtual content 46. The spatially-varying, rendered virtual content 46 presents a user virtual scene 50. In the user virtual scene 50, the portions / virtual objects 48_1 are rendered with less intensity (with more fade-out) than the portions / virtual objects 48_2. In this example, but not necessarily all examples, the portions / virtual objects 48_1 are rendered with 25% of the intensity of the default virtual content 42 and the portions / virtual objects 48_2 are rendered with 80% of the intensity of the default virtual content 42. Comparing a transition from FIG 5A to FIG 5C, the virtual content 42 is faded-out with the portions / virtual objects 48_1 being faded-out more significantly (more quickly) than the portions / virtual objects 48_2. Comparing a transition from FIG 5C to FIG 5A, the virtual content 42 is faded-in with the portions / virtual objects 48_2 being faded-in more significantly (more quickly) than the portions / virtual objects 48_1. FIG 6A illustrates the real-world content 32, that is content from the real-world 30. If the rendering device 20 transfers the real-world content 32 fully (full transparency) then the transferred external real-world content 34 is the real-world content 32 and the spatially-varying, transferred external real-world content 36 is the real-world content 32. The real-world content 32 comprises different portions and can comprise different real-world objects 38. As illustrated in FIG 6B the portions / objects 38 are classified 60 into different subsets 38_1, 38_2. In at least some examples, the subset 38_2 of the real-world content 32 corresponds to a contextually most important object or objects. As illustrated in FIG 60, the rendering device 20 transfers the real-world content 32 with spatial variation as spatially-varying, transferred external real-world content 36. The spatially-varying transferred external real-world content 36 presents a user real scene 52. In the user real scene 52, the portions / objects 38_1 are transferred with less transparency (more attenuation) than the portions / objects 38_2. In this example, but not necessarily all examples, the portions / objects 38_1 are transferred with 20% of the original intensity and the portions / objects 38_2 are transferred with 95% of the original intensity. Comparing a transition from FIG 6A to FIG 6C, the real-world content 32 is faded-out with the portions / objects 38_1 being faded-out more significantly (more quickly) than the portions / objects 38_2. Comparing a transition from FIG 6C to FIG 6A, the real-world content 32 is faded-in with the portions / objects 38_2 being faded-in more significantly (more quickly) than the portions / objects 38_1. The importance of an object can be dependent upon classification of the object. The classification of an object can, for example, use computer vision, audio analysis or associated metadata. For example a person may be considered more important than a pet and a pet may be considered more important than a television. The importance of an object can be dependent upon classification of the object using audio as a source of speech or other noise. For example, a person speaking and / or a person’s speech may be considered more important than a dog barking or the barking of a dog which may be considered more important than sound from a direction of a television. The importance of an object can be dependent upon a position and / or orientation of an object. For example a person, who has turned towards the user 2, may be considered more important than a person who is standing with their back to the user 2. The importance of an object can be dependent upon how the object has changed. For example, a person entering a room occupied by the user 2 (the object coming into existence) may be considered important whereas a person exiting the room would not be. The importance of an object can be dependent upon an assessment of its dominance in a scene. The rate at which an object is faded-in can be dependent upon an assessment of importance of the object, for example as described above. In at least some examples, the most important objects are faded-in faster than the least important objects. The rate at which an object is faded-out can be dependent upon an assessment of importance of the object, for example as described above. In at least some examples, the most important objects are faded-out slower than the least important objects. The importance of an object can be assessed, for example, by classifying the objects, and ranking the classified objects to select a limited number of the ranked objects (for example, visual objects and / or audio sources. The apparatus 10 and / or the rendering device 20 can comprise means for enabling user-control of: object classification, object ranking, the limited number of ranked objects, the fading-in rate, the fading-out rate. The apparatus 10 and / or the rendering device 20 can comprise means for enabling user-control of starting, stopping, pausing, freezing the fading process while virtual content continues to be rendered. FIG 7 illustrates that the rendering device 20 is configured to simultaneously provide, in overlap, the user virtual scene 50 and the user real scene 52 as a combined scene 54. The rendering device 20 performs (and the apparatus 10 controls) spatially-selective variation of a transfer of external real-world content 32 by the rendering device 20 to the user 2. The spatially-selective variation between portions / objects 38_2 and the portions / objects 38_1 makes the portions / objects 38_2 relatively more prominent than the portions / objects 38_1. Simultaneously, the rendering device 20 performs (and the apparatus 10 controls) spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. The spatially-selective variation between portions / virtual objects 48_2 and the portions / virtual objects 48_1 makes the portions / virtual objects 48_2 relatively more prominent than the portions / virtual objects 48_1. FIGs 8A to 8E illustrate a user virtual scene 50 during an evolving time sequence. FIGs 9A to 9E illustrate a user real scene 52 during an evolving time sequence. In the sequence illustrated in FIGs 8A to 8E, the rendering device 20 performs (and the apparatus 10 controls) spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. The virtual content 42 is being faded-out in a non spatially homogeneous way to form the spatially-varying, rendered virtual content 46. In the user virtual scene 50, the portions / virtual objects 48_1 are rendered with less intensity than the portions / virtual objects 48_2. In this example, but not necessarily all examples, the portions / virtual objects 48_1 are rendered with 80%, 50%, 25%, 10%. 0% of the intensity of the default virtual content 42 in respective FIGs 8A to 8E. The portions / virtual objects 48_2 are rendered with 100%, 100%, 80%, 50%. 20% of the intensity of the default virtual content 42 in respective FIGs 8A to 8E. In the sequence illustrated in FIGs 9A to 9E, the rendering device 20 performs (and the apparatus 10 controls) spatially-selective transfer of real-world content 32 by the rendering device 20 to the user 2. The real-world content 32 is being faded-in in a non spatially homogeneous way to form the spatially-varying, transferred external real-world content 36. In the user real scene 52, the portions / objects 38_1 are rendered with less intensity than the portions / objects 38_2. In this example, but not necessarily all examples, the portions / objects 38_1 are transferred with 0%, 10%, 20%, 25%. 50% of the intensity of the real-world content in respective FIGs 9A to 9E. The portions / objects 38_2 are rendered with 70%, 80%, 95%, 100%. 100% of the intensity of the real-world content 32 in respective FIGs 9A to 9E. FIGs 10A to 10E illustrate that the rendering device 20 is configured to simultaneously provide, in overlap, the user virtual scene 50 and the user real scene 52 as a combined scene 54. The rendering device 20 is configured to simultaneously vary spatially-selective transfer of external real-world content 32 by the rendering device 20 to the user 2 and spatially-selective rendering of virtual content 42 by the rendering device 20 to the user 2. There is synchronicity between FIGs 8A to 8E, FIGs 9A to 9E and Fig 10A to 10E, such that FIGs 8A, 9A, 10A are simultaneous, FIGs 8B, 9B and 10B are simultaneous, FIGs 8C, 9C and 10C are simultaneous, FIGs 8D, 9D and 10D are simultaneous, FIGs 8E, 9E and 10E are simultaneous. In at least some embodiments fading-in of the real-world content 32 commences before or simultaneously with fading-out of virtual content 42. In at least some embodiments fading-in of the content occurs first and / or fastest for the most important objects in the content (real-world content 32 and / or virtual content 42). In at least some embodiments fading-in of the content occurs last and / or slowest for the least important objects in the content (real-world content 32 and / or virtual content 42). In at least some embodiments fading-out of the content occurs first and / or fastest for the least important objects in the content (real-world content 32 and / or virtual content 42). In at least some embodiments fading-out of the content occurs last and / or slowest for the least important objects in the content (real-world content 32 and / or virtual content 42). Referring to FIGs 8A to 8E, the original virtual content is adapted to adapted virtual content 46 to decrease an intensity of rendering (fading-out) of the virtual content 42 associated with a portion 48_2 of the user virtual scene 50 more than an intensity of rendering (fading-out) the virtual content 42 associated with a different portion 48_1 of the user virtual scene 50. This is performed while maintaining the association of the virtual content 42 with the same portions of user virtual scene 50. That is the intensity of virtual objects 48 are adapted (faded) but they are not re-sized or moved. Referring to FIGs 9A to 9E, over time there is an increasing transfer (fading-in) of external real-world content 32 associated with a first portion 38_2 of a user real scene 52 and increasing transfer (fading-in) of external real-world content 32 associated with a second portion 38_1 of the user real scene 52. The initial rate of increase of the transfer (fading-in) of external real-world content 32 associated with the first portion 38_2 of the user real scene 52 is greater than the rate of increase of transfer (fading-in) of external real-world content 32 associated with the second portion 38_1 of the user real scene 52. This provides spatially-selective variation of transfer (and fading) of external real-world content 32 by the rendering device 20 to the user 2. Referring to FIGs 10A to 10E, the FIGs illustrate fading-in spatially selective transferred external real-world content 36 associated with one or more fade-in portions of a user combined scene 54 while simultaneously fading-out spatially-selective virtual content 46 associated with one or more fade-out portions of the user combined scene 54. The fading-in is at a faster rate at a portion 38_2 of the combined scene 54 limited to a real-world object, for example real-world visual object or a real-world audio source. Fading-in the external real-world content 32 can be limited to occur at only the portion 38_2 of the scene limited to a selected one or more real-world visual objects and / or one or more real-world audio sources. The fading-in can be at a faster rate at a portion of the scene 54 limited to a real-world visual object or real-world audio source . The fading-out is at a faster rate at a portion 48_2 of the scene 54 limited to a virtual object, for example a virtual visual object or a real-world audio source. Fading-out the virtual content 46 can be limited to occur at only the portion of the virtual scene 52 not limited to a selected one or more virtual visual objects and / or one or more virtual spatial audio sources. The fading-out can be at a slower rate at a portion of the scene 54 limited to a virtual visual object or virtual audio source compared to portions of the virtual scene 52 not limited to the selected one or more virtual visual objects and / or one or more virtual spatial audio sources. Referring to FIG 10A, the one or more fade-in portions 38_2 of the scene 54 have a combined area that is significantly smaller than a combined area of the one or more fade-out portions of the scene 54. Referring to FIGs 10A to 10E, there is fading-in at different rates at different ones of the one or more fade-in portions of the scene 54 and / or fading-out at different rates at different ones of the one or more fade-out portions of the scene 54. There can be means for fading-in, visually, spatially selective external real-world visual content 76 within a visual scene while simultaneously fading-out spatially-selective virtual visual content 76 across the visual scene and / or means for fading-in, acoustically, spatially selective external real-world 30 audio content 72 across an audio scene while simultaneously fading-out spatially-selective virtual audio content 72 across the audio scene. FIGs 11A-11C, 12A-12C and 13 illustrate different fade-in rates for different real-world content portions / objects 38. An object 38 is classified as an object 38_3 of importance that is less important that the object 38_2 and more important than the other content portions / objects 38_1. During fade-in, the object 38_2 is faded-in faster than the object 38_3, which is faded in faster than the objects 38_1. FIGs 11A-11C are the same as FIGs 5A-5C, for the purpose of continuity of description. FIGs 12A-12C are the same as FIGs 6A-6C, except that there is an additional portion / object 38 in the real-world content 32 which is differently classified 38 as portion / object 38_3. The spatially-varying, transferred external real-world content 36 has different transfer values for the portions / objects 38_1, 38_2, 38_3. The real-world content 32 comprises different portions and can comprise different real-world objects 38.The portions / objects 38 are classified 60 into not only subsets 38_1, 38_2 as previously (not labelled) but also subset 38_3. The portions / objects 38_1 are transferred with less transparency (more attenuation) than the portions / objects 38_3. The portions / objects 38_3 are transferred with less transparency (more attenuation) than the portions / objects 38_2. In this example, but not necessarily all examples, the portions / objects 38_1 are transferred with 20% of the original intensity, the portions / objects 38_1 are transferred with 50% of the original intensity, and the portions / objects 48_2 are transferred with 95% of the original intensity. Comparing a transition from FIG 12A to FIG 12C, the real-world content 32 is faded-out with the portions / objects 38_1 being faded-out more significantly (more quickly) than the portions / objects 38_3 and with the portions / objects 38_2 being faded-in more significantly (more quickly) than the portions / objects 38_3. Comparing a transition from FIG 6C to FIG 6A, the real-world 30 is faded-in with the portions / objects 38_2 being faded-in more significantly (more quickly) than the portions / objects 38_3 and with the portions / objects 38_3 being faded-in more significantly (more quickly) than the portions / objects 38_1. FIG 13 is the same as FIG 7 except that the transferred external real-world content 36 from the user real scene 52 is different because it additionally comprises a partially faded-in portion / object 38_3 that has a transfer value intermediate that of the portions / objects 38_1 and the portions / objects 38_2. FIGs 14A-14E, 15A-15E, 16A-16E illustrate the user virtual scene 50, the user real scene 52 and the combined scene 54. FIGs 14A-14E are the same as FIGs 8A-8E , for the purpose of continuity of description. FIGs 15A-15E are the same as FIGs 9A-9E except that there is an additional portion / object 38 in the real-world content 32 which is differently classified as portion / object 38_3. The spatially-varying, transferred external real-world content 36 has different transfer values for the portions / objects 38_1, 38_2, 38_3. The fade-in rate for the portions / objects 38_2 is more that the fade-in rate for the portions / objects 38_3. The fade-in rate for the portions / objects 38_3 is more that the fade-in rate for the portions / objects 38_1. In the user real scene 52, the portions / objects 38_1 are presented with slower fade-in than the portions / objects 38_3. In this example, but not necessarily all examples, the portions / objects 38_1 are transferred with 0%, 10%, 20%, 25%. 50% of the intensity of the real-world content in respective FIGs 15A to 15E. The portions / objects 48_3 are rendered with 0%, 10%, 50%, 100%. 100% of the intensity of the real-world content 32 in respective FIGs 15A to 15E. In the user real scene 52, the portions / objects 38_3 are rendered with slower fade-in than the portions / objects 38_2. In this example, but not necessarily all examples, the portions / objects 48_2 are rendered with 70%, 80%, 95%, 100%. 100% of the intensity of the real-world content 32 in respective FIGs 15A to 15E. In at least some examples, the fade-in of the portions / objects 38_3 is delayed and / or less fast relative to the fade-in of the portions / objects 38_2. The fade-in of the portions / objects 38_1 is delayed and / or less fast relative to the fade-in of the portions / objects 48_3. FIGs 16A-16E are the same as FIGs 10A-10E except that the transferred external real-world content 36 from the user real scene 52 is different because it additionally comprises a partially faded-in portion / object 38_3 that has a fade-in rate intermediate that of the portions / objects 38_1 and the portions / objects 38_2. In an example use case, a user 2 starts in a virtual reality (VR) world. The apparatus 10 controls fade-in of the most important content portions / objects 38 from the real-world (real-world content 32) and only then the rest of the real-world content 32 from the real-world 30. Objects of interest are detected either periodically, continuously, or when the user starts to perform a fade towards another reality, for example, such as from virtual reality towards the augmented reality, for example, see-through mode. Multiple objects may be classified / identified and ranked based on importance. Identification / classification is performed for visual content and / or audio content. Identification / classification of important objects and their ranking may depend on (but not limited to): Persons, pets, and alike in the scene Object that the user may interact with Key objects that relate to the current activity, such as game Sudden audio event or otherwise important audio is recognized, such as speech Audio event towards the user or new audio event of interest New object emerging and / or approaching the user Unexpected change in the scene (real-world or virtual world), for example, dialog in a game, explosion or other sudden event in a game, object dropping to floor in real world. The ranking between the different content / objects may be done automatically or it may include user preference and / or filtering. It is also possible that the key important content does not always include visuals as the content 70 may not be visible 76 but only audible 72, for example, someone calling you from another room. In this case the audio 38_2 from the important direction will be fadedin first before fading-in other audio 38_1, 38_3 from the real-world scene. In examples, the important audio content 72 may be faded-in first, followed by related visual content 76 (for example, visual direction if no objects of interest are present), followed by rest of audio and visual content 72, 76. The spatial audio content (i.e., audio directions) from virtual and real-world can be fadedin and faded-out together (but not necessarily in synchronicity) regardless of whether the audio content is coupled with important visual content or not. In one example, a user 2 is enjoying a beach scene game in VR but something is going on in the real world 30 as the user 2 hears a quiet mumble (or is being notified about changes in the real-world 30). The user 2 wants to address the situation and starts fading-in towards the see-through view or a fade-in starts automatically. The most important real-world content 32 (including visual content 76 and audio content 72) is being faded-in first: a talking wife and a ringing mobile device are identified as most important in the real-world scene (real-world content 32). While the user 2 is fadingin the see-through view (real-world content 32), the wife and the mobile device (objects 38_2) are faded-in first but the user 2 is still able to see some or all of the virtual reality scene (virtual content 42) well. The user 2 keeps on fading-in the see-through view (real-world content 32), and a dog (silent), identified as an object of interest 38_3 is faded in before the rest 38_1 of the see-through view (content / objects 38_2). If the user keeps on fading-in, the real-world scene (real-world content 32), will be fully visible (and audible). Regardless of having multiple stages in the fade-in, the user 2 is still able to switch between the views quickly and easily. In an example use case, a user 2 starts in a virtual reality (VR) world. The apparatus 10 controls fade-out of the most important content / objects 48_2 from the virtual world (virtual content 42) last and only then the rest of the content / objects 48_1 from the virtual world (virtual content 42). This fade-out can occur independently of fade-in of the real-world (real-world content 32), or can occur simultaneously with fade-in of the real-world (real-world content 32),. In the VR scene (virtual content 42), a man standing in front with a beach ball facing the user 2 is considered to be most important visual virtual content as there is constant interaction with the user in the VR game. In this embodiment while fading-in the real world (virtual content 42), the important virtual objects 48_2 will be faded-out last, being maintained while the most important real-world objects 38_2, 38_3 have been faded in. In further examples, there can be a matching of important objects in VR world (virtual content 42), and real world (real-world content 32), for example, same person is part of the real-world surroundings real-world content 32) and an immersive holiday memory content. This may change the ranking of the importance. Furthermore, in some examples there is an impact on fading if there are similarities in the virtual and real world scene (virtual content 42 and real-world content 32), for example The apparatus 10 or rendering device 20 is configured to select a suitable mix between the realities for new enhanced user experiences. The user 2 may seamlessly adjust the balance between the real and the virtual world (virtual content 42 and real-world content 32) to be able to have a better experience compared to purely hard-switching between the modes and potentially pausing the VR experience or missing important real-life events. Similarly, the user may easily continue the VR experience while blending in the real world just a bit. In an example there could be a fading stage between the realities where the user 2 has the important objects simultaneously visible from the real-world 38_2, 38_3 and from the virtual world 48_2 and is able to get best from both realities without the need for pausing the VR experience and ignoring real-life events. New important sources may appear and be included into the fade process dynamically. For example, if the dog in the real-world starts moving and / or barking, its importance can increase and it can be faded-in sooner or more quickly. The dog may now either override a previously important object or be added as another important object. This may depend on the implementation and for example user interaction (for example, gaze direction). In another example implementation, the user is provided with haptic feedback or other types of notification when for example new important content is detected, for example real-world important objects. The feedback may be directional. There may be a limit, for example, user set limit for total important objects to have special fade-in / fade-out functionality to avoid too much information / overlap. This type of limit may change the rendering of the scene, for example, only the most currently important source, source which the user can interact with, audible source etc. The limits may be set automatically or be user defined or may be scene and / or content specific. Also, number of important objects (or levels of fade-in / fade-out) will impact the time it will take to cycle through each individual fading level between the two realities. Thus, it can be useful to limit the number in practical applications. On the other hand, in some examples, there can be an extremely high number of the objects / levels, and user can, for example, fine-tune the desired balance of the mix between the two realities over time and maintain this.) Beamforming and sound source separation and other techniques, such as machine learning, can be used to fade-in / fade-out sound sources, for example real-world sound objects, differently. FIG 17 illustrates an example of a method 500. The method 500 can, for example, be used to gradually fade-in / fade-out between realities. At block 502, the method 500 comprises controlling spatially-selective variation of a transfer of external real-world content by a rendering device to a user. At block 504, the method 500 comprises controlling spatially-selective rendering of virtual content by the rendering device to the user. Fig 18 illustrates an example of a controller 400 suitable for use in an apparatus 10, 20, for example as control means 12. Implementation of a controller 400 may be as controller circuitry. The controller 400 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). As illustrated in Fig 18 the controller 400 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 406 in a general-purpose or special-purpose processor 402 that may be stored on a computer readable storage medium (disk, memory etc) to be executed by such a processor 402. The processor 402 is configured to read from and write to the memory 404. The processor 402 may also comprise an output interface via which data and / or commands are output by the processor 402 and an input interface via which data and / or commands are input to the processor 402. The memory 404 stores a computer program 406 comprising computer program instructions (computer program code) that controls the operation of the apparatus 10, 20 when loaded into the processor 402. The computer program instructions, of the computer program 406, provide the logic and routines that enables the apparatus to perform the methods illustrated in the accompanying Figs. The processor 402 by reading the memory 404 is able to load and execute the computer program 406. The apparatus 10, 20 comprises: at least one processor 402; and at least one memory 404 including computer program code, the at least one memory storing instructions that, when executed by the at least one processor 402, cause the apparatus at least to: control spatially-selective variation of a transfer of external real-world content by a rendering device to a user; and control spatially-selective rendering of virtual content by the rendering device to the user. As illustrated in Fig 19, the computer program 406 may arrive at the apparatus 10, 20 via any suitable delivery mechanism 408. The delivery mechanism 408 may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 406. The delivery mechanism may be a signal configured to reliably transfer the computer program 406. The apparatus 10, 20 may propagate or transmit the computer program 406 as a computer data signal. Computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: controlling spatially-selective variation of a transfer of external real-world content by a rendering device to a user; and controlling spatially-selective rendering of virtual content by the rendering device to the user. The computer program instructions may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program. Although the memory 404 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage. Although the processor 402 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 402 may be a single core or multi-core processor. References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be 27 understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. As used in this application, the term ‘circuitry’ may refer to one or more or all of the following: (a) hardware-only circuitry implementations (such as implementations in only analog and / or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory or memories that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device. The blocks illustrated in the accompanying Figs may represent steps in a method and / or sections of code in the computer program 406. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted. Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described. As used here ‘module’ refers to a unit or apparatus that excludes certain parts / components that would be added by an end manufacturer or a user. The apparatus 10 can be a module, for example it can be a module comprised in a rendering device 20. The above-described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and / or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services. The apparatus can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certain implementation examples, the apparatus can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility. The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one...” or by using “consisting”. In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., so as to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components. As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also," determine / determining" can include resolving, selecting, choosing, establishing, and the like. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. Whilst endeavoring in the foregoing specification to draw attention to those features 5 believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. 10 l / we claim: 15

Claims

1. An apparatus comprising:control means for controlling presentation of content by a rendering device to a user, wherein the control means is configured to:provide spatially-selective variation of a transfer of real-world content by the rendering device to the user;andcause provision of a spatially-selective rendering of virtual content by the rendering device to the user.

2. An apparatus as claimed in claim 1 configured to provide control signals to the rendering device, wherein the control signals are:configured to control a visual transparency of a head-mounted display to provide a spatially-selective variation of visual transparency of the display which provides a spatially-selective variation of a transfer of real-world visual content to the user;and / orconfigured to provide control signals to the rendering device, wherein the control signals are configured to control spatial rendering of audio sources to provide a spatially-selective variation of audio transparency to the real-world space which provides a spatially-selective variation of a transfer of real-world audio content to the user.

3. An apparatus as claimed in claim 1, or 2 comprising:means for controlling simultaneously variation of:spatially-selective transfer of real-world content by the rendering device to the user; andspatially-selective rendering of virtual content by the rendering device to the user.

4. An apparatus as claimed in any preceding claim, wherein the control means comprises:means for increasing transfer of real-world content associated with a first portion of a scene and for increasing transfer of real-world content associated with a second portion of the scene, configured to increase the transfer of real-world content associated with the first portion of the scene more than the transfer of real-world content associated with the second portion of the scene which provides spatially-selective variation of transfer of real-world content by the rendering device to the user.

5. An apparatus as claimed in claim 4, wherein the control means comprises adapting means for adapting virtual content to decrease an intensity of rendering the virtual content associated with a third portion of the scene more than an intensity of rendering the virtual content associated with a fourth portion of the scene.

6. An apparatus as claimed in claim 5, wherein the adapting means is configured to decrease an intensity of rendering the virtual content associated with the third portion of the scene more than an intensity of rendering the virtual content associated with the fourth portion of the scene while maintaining the association of the virtual content with the same portions of scene.

7. An apparatus as claimed in any preceding claim, comprising fading means for fading-in spatially selective real-world content associated with one or more fade-in portions of a scene while simultaneously fading-out spatially-selective virtual content associated with one or more fade-out portions of the scene.

8. An apparatus as claimed in claim 7, wherein the one or more fade-in portions of the scene have a combined area that is smaller than a combined area of the one or more fade-out portions of the scene.

9. An apparatus as claimed in claim 7 or 8, wherein the fading means is configured to fade-in at different fade-in rates at different ones of the one or more fade-in portions of the scene and / or fade-out at different fade-out rates at different ones of the one or more fade-out portions of the scene.

10. An apparatus as claimed in any of claim 7 to 9, wherein the fading means is configured to fade-in at a faster rate at a portion of the scene limited to a real-world visual object or real-world audio source.

11. An apparatus as claimed in any of claim 7 to 10 comprising:means for classifying real-world visual objects and / or real-world audio sources to select one or more real-world visual objects and / or one or more real-world audio sources; and means for fading-in real-world content at a portion of the scene limited to the selected one or more real-world visual objects and / or one or more real-world audio sources.

12. An apparatus as claimed in claim 11 comprising means for ranking the classified real-world visual objects and / or classified real-world audio sources to select a limited number of the ranked real-world visual objects and / or real-world audio sources.

13. An apparatus as claimed in claim 12 comprising means for enabling user control of at least one of: classifying, ranking, the limited number of the ranked real-world visual objects and / or real-world audio sources, a fading-in rate.14.. An apparatus as claimed in any of claim 7 to 13, wherein the fading means is configured to fade-out at a slower rate at a portion of the scene limited to a virtual visual object or virtual audio source compared to a portion of the scene not limited to the virtual visual object or the virtual audio source.

15. An apparatus as claimed in any of claim 7 to 14, comprising:means for classifying virtual objects and / or virtual audio sources in the virtual content to select one or more virtual visual objects and / or one or more virtual audio sources; and means for fading-out virtual content at a portion of the scene not limited to the selected one or more real-world visual objects and / or audio sources.

16. An apparatus as claimed in claim 15, comprising means for ranking the classified virtual visual objects and / or virtual audio sources to select a limited number of the ranked virtual visual objects and / or virtual audio sources.

17. An apparatus as claimed in claim 16, comprising means for enabling user control of at least one of: classifying virtual objects and / or virtual audio sources , ranking classified virtual visual objects and / or virtual audio sources, the limited number of the ranked virtual visual objects and / or virtual audio sources, a fade-out rate.

18. A system comprising the apparatus as claimed in any preceding claim and the rendering device, wherein the rendering device comprises a head-mounted display configured to visually isolate a user’s eyes, from an external real-world space external to the rendering device, in an internal space wherein a display provides an interface between the internal space and the external real-world space and wherein a visual transparency of the display is controllable to provide a spatially-selective variation of visualtransparency to the external real-world space which provides spatially-selective variation of the transfer of external real-world visual content to the user;and / orwherein the rendering device comprises a head-mounted spatial audio system configured to audibly isolate a user’s ears, from an external real-world space external to the rendering device, in an internal space wherein one or more spatial audio channels provide an interface between the internal space and the external real-world space and wherein a spatial rendering of external audio sources is controllable to provide a spatially-selective variation of audio transparency to the external real-world space which provides spatially-selective variation of the transfer of external real-world audio content to the user.

19. A method comprising:controlling spatially-selective variation of a transfer of real-world content by a rendering device to a user;andcontrolling spatially-selective rendering of virtual content by the rendering device to the user.

20. A computer program that, when run on a computer, performs: controlling spatially-selective variation of a transfer of real-world content by a rendering device to a user;andcontrolling spatially-selective rendering of virtual content by the rendering device to the user.

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