Graphics texture mapping

Abstract

When anisotropic filtering is performed while sampling a texture to provide output sampled texture values for use in rendering an output in a graphics processing system, an anisotropic direction along which a sample is to be acquired in the texture is determined by determining X and Y components of an arbitrary length vector, the arbitrary length vector corresponds to a direction from a sampling point at which the texture is sampled to a long axis of a hypothetical elliptical projection on a surface to which the texture is applied; the determined X vector component and the determined Y vector component are then normalized to provide X and Y components of a unit vector corresponding to the direction of the long axis of the elliptical footprint of the sampling point for use as the anisotropic direction along which samples are to be acquired in the texture.

Description

technical field [0001] The present invention relates to a method and apparatus for performing texture mapping in a graphics processing system. Background technique [0002] It is common in graphics processing systems to generate colors (and other data) for sampling locations in a rendered output (eg, an image to be displayed) by applying so-called textures or texture data to a surface to be drawn. [0003] A computer graphics texture will typically be configured as an array of texture data elements (texels), each texture data element having a corresponding set of texture data (such as color, brightness, and / or light / shading, etc.) stored for it. The sample locations in the rendered output where the texture is to be applied are then mapped to corresponding locations in the texture and the texture sampled at that location using an appropriate filtering process, such as a bilinear filtering process, to determine the samples to use in the rendered output The texture data for th...

AI Technical Summary

Problems solved by technology

[0019] While it is possible to determine the projected ellipses and the corresponding ellipse parameters in order to perform anisotropic filtering with high accuracy, this is relatively expensive to implement in hardware, and generally speaking, for performing Methods of anisotropic filtering tend to use approximations when determining ellipse parameters, such as trying to find the best match to a set of reference anisotropy directions for a given anisotropic filtering operation, rather than determining the actual anisotropy direction itself

However, applicants have realized that using such approximations for anisotropic filtering may lead to visual artifacts and, in particular, may give incorrect results about the angle of the major axis of the ellipse, and that these errors may also exhibit certain Angle dependence (i.e. greater for some angles than others)

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