Variable Rate Shading Bandwidth Allocation
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Solution Overview
Problem
Current 3D graphics processing pipelines face inefficiencies in pixel shading due to the resource-intensive nature of rasterization and pixel shading being performed at the same resolution, leading to redundant operations for triangles with fixed colors or low frequency changes, which can be improved by decoupling rasterization and shading resolutions.
Innovation Solution
Implementing a variable rate shading technique where rasterization occurs at a different resolution than pixel shading, down-sampling fragments to coarse ones, shading them, and then up-sampling to fine fragments, reducing the number of pixel shader operations and enhancing bandwidth utilization by repurposing blending bandwidth for outputting fragments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rasterization and pixel shading are performed at the same resolution, then rendering accuracy is maintained, but processing load and resource consumption increase due to redundant operations
Solution Approach 1:
The patent segments the rendering process into two distinct resolution stages: a lower-resolution rasterization stage that generates coarse fragments, and a higher-resolution shading stage that processes fine fragments. This segmentation allows redundant operations to be eliminated at the rasterization stage while maintaining final rendering quality through the subsequent up-sampling and shading process.
Solution Approach 2:
The patent applies local quality by processing different regions of the image at different resolutions during rasterization. Areas with simple geometry or uniform properties are rasterized at lower resolution, while areas requiring higher detail are processed at full resolution. This selective approach reduces overall processing load while maintaining rendering accuracy where needed.
2Productivity
If variable rate shading is implemented with down-sampling to coarse fragments, then pixel shader operations are reduced, but additional processing steps and bandwidth management complexity are introduced
Solution Approach 1:
The patent merges the up-sampling operation with the pixel shading process by performing both operations in a single unified stage. Instead of treating up-sampling and shading as separate sequential steps, the system combines them into one integrated processing pass, thereby reducing the total number of processing steps while still achieving the benefits of variable rate shading.
Solution Approach 2:
The patent implements multi-functionality by designing the pixel shader stage to simultaneously perform multiple tasks: up-sampling coarse fragments to fine fragments, applying shading calculations, and managing bandwidth allocation. This universal approach consolidates what would otherwise be separate processing functions into a single versatile stage, reducing overall system complexity.
3Productivity
If blending bandwidth is repurposed for outputting fragments in variable rate shading mode, then throughput is increased, but blending functionality must be disabled or suspended
Solution Approach 1:
The patent implements dynamic bandwidth allocation where the blending bandwidth is dynamically reassigned based on operational mode. In variable rate shading mode, the bandwidth is dynamically switched to support high-throughput fragment output. In blending mode, the same bandwidth is dynamically reallocated to support color blending operations. This dynamic switching allows the system to optimize for either throughput or versatility depending on the current rendering requirements.
Solution Approach 2:
The patent employs periodic switching between different bandwidth allocation patterns corresponding to different operational modes. The system alternates between high-throughput fragment output patterns and color blending patterns based on the current rendering task requirements. This periodic reconfiguration of bandwidth usage allows the system to achieve high throughput during variable rate shading operations while maintaining the capability to perform blending when needed.
Data Source
AI summary
Techniques for processing pixel data are provided. The techniques include, in a first mode in which blending is enabled, reading in render target color data from a memory system; blending the render target color data with one or more fragments received from a pixel shader stage to generate blended color data; outputting the blended color data to the memory system utilizing a first amount of bandwidth; in a second mode in which blending is disabled and variable rate shading is enabled, amplifying shaded coarse fragments received from the pixel shader stage to generate fine fragments; and outputting the fine fragments to the memory system utilizing a second amount of bandwidth that is higher than the first amount of bandwidth.