Advanced API Performance: Clears

This post covers best practices for clears on NVIDIA GPUs. To get a high and consistent frame rate in your applications, see all Advanced API Performance tips.

Surface clearing is a widely used accessory operation.

Recommended

• Use clear functions from the graphics API to clear resources.
• Use any clear color to clear render targets.
  • Hardware optimizations improves the most clear operations.
• Use a suitable clear value when clearing the depth buffer.
  • Prefer clear values within the range [0.0, 0.5) when using depth test functions D3D12_COMPARISON_FUNC_GREATER or D3D12_COMPARISON_FUNC_GREATER_EQUAL
  • Prefer clear values within the range [0.5, 1.0] when using depth test functions D3D12_COMPARISON_FUNC_LESS or D3D12_COMPARISON_FUNC_LESS_EQUAL.
• Group clear operations into as few batches as possible.
  • Batching reduces the performance overhead of each clear.

Not recommended

• Avoid using more than a few different clear colors for surface clearing.
  • Clearing optimization limited to 25 clear colors per frame on NVIDIA Ampere Architecture GPUs.
  • Clearing optimization limited to 10 clear colors per frame on NVIDIA Turing GPUs.
• Avoid interleaving single clear calls with rendering work.
  • Group clears into batches whenever possible.
• Never use clear-shaders as a replacement for API clears.
  • It disables hardware optimizations and negatively impacts both CPU and GPU performance.
  • Exception: Overlapping a compute clear with neighboring compute work may give better performance.

Acknowledgments

Thanks to Michael Murphy, Maurice Harris, Dmitry Zhdan, and Patric Neil for their advice and feedback.