MSAA-Based Coarse Shading for Power-Efficient Rendering on High Pixel-Density Displays

TitleMSAA-Based Coarse Shading for Power-Efficient Rendering on High Pixel-Density Displays
Publication TypeConference Paper
Year of Publication2015
AuthorsMavridis, P, Papaioannou, G
Conference NameHigh Performance Graphics (poster and quick talk)

Maintaining real-time frame rates at the native resolution of high pixel-density displays is very challenging, especially on power-constrained mobile devices. Decoupled sampling approaches offer a better solution to this problem, compared to rendering at a lower resolution and up-scaling, by sampling the visibility at a higher rate than shading, thus preserving the clarity of geometric edges, while reducing the cost of shading. However, this ability is rather limited in current graphics architectures, where the widely-used MSAA algorithm shades each covered primitive at least once per pixel, without directly providing the ability to compute pixel shading at a more coarse rate. While various extensions of the graphics pipeline for coarse shading have been proposed, in this work we focus on a software implementation for existing GPUs. To this end, we render an intermediate render buffer at a lower pixel count, but at the same time we compensate the loss in resolution by adding the appropriate amount of MSAA sub-pixel samples, in order to guarantee at least one visibility sample per display pixel. Subsequently, a custom resolve shader is used to perform the mapping of sub-pixel MSAA samples to pixels. This simple technique effectively shades more coarsely pixel blocks, where there are no geometric edges. While variations of this idea have been previously used on game consoles, a proper evaluation of the effectiveness of this method at decreasing shader invocations and energy consumption is missing from the bibliography and is our main contribution. We demonstrate our method on several test scenes with varying degrees of geometric and shading complexity and our measurements indicate an up to 45% reduction in energy consumption.