The Motion class provides functions for calculating motion vectors, reprojection, and performing temporal filtering in HLSL shaders. It is useful for implementing effects like Temporal Anti-Aliasing (TAA), motion blur or general reprojection by blending current and previous frame data.

⚠️ Right now this is limited to camera motion only, moving objects currently do not react to their own motion.

API

float3 Motion::GetFromWorldPosition(float3 worldPosition)

• Reprojects a world-space position to screen-space ( Depth in Z ) coordinates using the last frame's depth buffer.

float3 Motion::Get(float2 screenPosition)

• Returns the position in clip space ( Pixel Position + Depth in Z ) of where this pixel was projected on the previous frame.

float4 Motion::TemporalFilter( uint2 vPositionSs, Texture2D tCurrent, Texture2D tPrev, float flBlendWeight = 0.9f )

• A traditional Temporal Anti-Aliasing filter, takes the position of the current pixel and the texture of the current frame, and previous frame and using the motion vectors to blend them.

• It works as follows:

  • Calculate Previous Frame UV Coordinates:

    • Uses motion vectors to find where the current pixel was in the previous frame.

    • Converts screen-space position to UV coordinates for texture sampling.

  • Compute Min and Max Sample Values:

    • Iterates over a 3x3 pixel neighborhood around the current pixel.

    • Finds the minimum and maximum color values to clamp the previous frame's sample.

  • Sample Previous Frame Texture:

    • Samples the previous frame's texture at the calculated UV coordinates using bilinear filtering.

  • Clamp Previous Frame Sample:

    • Ensures the previous frame's data does not introduce artifacts when blending using a bounding box of colors.

  • Blend Samples:

    • Blends the current frame's sample with the clamped previous frame's sample based on the blend weight.