Tile-Based Immediate Mode Rendering Prefetch Mechanism
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Solution Overview
Problem
Current Tile-Based Immediate Mode Rendering (TBIMR) architectures face limitations due to on-chip buffer constraints, where geometry data and pointers must be spilled to memory when buffers are filled, leading to incomplete render passes and increased memory access latency.
Innovation Solution
Implementing an intelligent prefetch mechanism and memory-backed geometry storage, where geometry data is spilled to memory and then prefetched back when on-chip buffers become available, along with occlusion culling using per-tile 3D bounding boxes for efficient rendering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If geometry data is stored in on-chip buffers, then rendering speed is improved, but buffer capacity is limited causing data to be spilled to memory
Solution Approach 1:
The patent implements an intelligent prefetch mechanism that anticipates which geometry data will be needed next and pre-loads it into on-chip buffers before it is actually required for rendering. This preliminary action ensures that data is ready in fast memory when needed, maintaining high rendering speed while efficiently utilizing limited buffer capacity.
Solution Approach 2:
The patent divides geometry data into tile-based segments and processes them in organized chunks. By segmenting the rendering workload into manageable tile units with associated pointer queues, the system can efficiently manage limited on-chip buffer capacity while maintaining continuous rendering throughput.
2Productivity
If buffers are filled with geometry data, then rendering throughput is improved, but buffer flush operations increase memory latency
Solution Approach 1:
The patent maintains continuous rendering throughput by implementing a memory-backed geometry storage system with intelligent prefetching. Instead of stopping for buffer flushes, the system continuously feeds geometry data from memory into on-chip buffers through prefetch mechanisms, eliminating idle time and maintaining uninterrupted rendering throughput.
Solution Approach 2:
The patent introduces an intermediary prefetch buffer layer between main memory and the rendering pipeline. This intermediary structure holds geometry data in an intermediate state, allowing the renderer to consume data from the prefetch buffer without directly stalling on slow memory accesses, thus reducing the impact of memory latency on overall throughput.
3Productivity
If complete render passes are achieved on chip, then rendering efficiency is improved, but on-chip memory bandwidth is limited
Solution Approach 1:
The system performs preliminary prefetching of geometry data into on-chip buffers before rendering begins for each tile. By having data ready in advance in the on-chip geometry buffer, the system can achieve complete render passes on-chip without stalling for memory accesses during the actual rendering process.
Solution Approach 2:
The patent introduces a time dimension to the memory hierarchy by implementing prefetching operations that occur in advance of rendering. This temporal separation allows geometry data to be loaded into on-chip buffers during idle periods or in parallel with other tile processing, effectively increasing available bandwidth without requiring more physical memory resources.
Data Source
AI summary
A virtual reality apparatus and method are described for tile-based rendering. For example, one embodiment of an apparatus comprises: a set of on-chip geometry buffers including a first buffer to store geometry data, and a set of pointer buffers to store pointers to the geometry data; a tile-based immediate mode rendering (TBIMR) module to perform tile-based immediate mode rendering using geometry data and pointers stored within the set of on-chip geometry buffers; spill circuitry to determine when the on-chip geometry buffers are over-subscribed and responsively spill additional geometry data and/or pointers to an off-chip memory; and a prefetcher to start prefetching the geometry data from the off-chip memory as space becomes available within the on-chip geometry buffers, the TBIMR module to perform tile-based immediate mode rendering using the geometry data prefetched from the off-chip memory.