Motion Blur

After a bit of research into different methods of implementing the feature, we based our implementation of motion blur on the method outlined in Nvidia's GPU Gems 3, and modified it with a custom weighted average. The motion vectors are pulled from the existing buffer, and are then used as the path that each colour sample is taken from for use in the final average. To make the blur respond to different magnitudes and directions of motion, I weighed each colour sample across the pixel path by its unique motion vector projected onto the origin pixel's motion vector. This prevents pixels undergoing significant motion from sampling static pixels for motion blur. Motion blur intensity is made inversely proportional to the current frame time to make the perceived motion blur intensityremain the same no matter the current framerate.

// Get motion vector UV for this pixel float2 motionUv = inputBufferMotionVectors[ipos]; // Full intensity at MOTION_BLUR_TARGET_FRAMETIME, make intensity inversely proportional to frametime float frameTimeFactor = MOTION_BLUR_TARGET_FRAMETIME / frameTime; // Multiply by display resolution to get velocity in pixels float2 motionPixels = -motionUv * MOTION_BLUR_INTENSITY * frameTimeFactor * g_view.displayResolution; // Clamp length to range from 0 to max motion blur length motionPixels *= saturate(MOTION_BLUR_MAX_LENGTH / length(motionPixels)); // Distribute pixel velocity over sample count float2 velocity = motionPixels / float(MOTION_BLUR_SAMPLES); float2 spos = float2(ipos) + velocity; float mtotalWeight = 1.0; [unroll] for (uint s = 1; s < MOTION_BLUR_SAMPLES; s++, spos += velocity) { if (any(spos <= 0) || any(spos >= g_view.renderResolution)) continue; float2 thisMotionUv = inputBufferMotionVectors[round(spos)]; // Weigh by vector similarity so that motion blur doesn't sample from static areas float sampleWeight = saturate(dot(thisMotionUv, motionUv) / dot(motionUv, motionUv)); mtotalWeight += sampleWeight; // Sample the color buffer along the velocity vector float3 currentColor = inputThisFrameTAAHistory[round(spos)].rgb; // Add the weighted sample to final colour finalColour += currentColor * sampleWeight; } // Average all of the samples to get the final blur colour finalColour /= mtotalWeight;