taau_resolve

One composite-resolution pixel per invocation: read the presented frame, find where its surface was last frame, and mix the accumulation into it.

The pass runs at a post-scene phase, where @scene.color is the composited image — the display's own resolution while the renderer presents the viewport itself — while @scene.depth and @scene.motion stay at the resolution the scene was rasterized into. Every read of the scene buffers maps the composite pixel back into that grid; the velocity it finds there is in NDC, which is the same span at either resolution.

binding	what it is
scene_color	the presented frame, composite resolution
scene_depth	scene depth, scene resolution, reversed (near = 1)
scene_motion	scene motion in NDC, scene resolution
taau_history	what this pass resolved last frame, composite resolution
taau_params	(historyWeight, neighbourhoodClamp, sharpness, motionRejection)
taau_state	(historyValid, jitterX, jitterY, _) — historyValid is 0 on the first frame of a run; the jitter is the NDC offset the projection carried for the frame being read, which is what places each scene sample inside the pixel
taau_out	this frame's resolve, composite resolution

Four things keep the accumulation honest:

• Sample-position weighting. Each of the 4x4 scene taps is weighted by how far its own sample landed from this pixel's centre, jitter included — so a frame that sampled elsewhere contributes little and one that sampled here carries the pixel. Reading the same neighbourhood unweighted would average away exactly the detail the jitter sequence is resolving.
• Velocity dilation. The velocity is taken from the nearest of the 3x3 scene neighbourhood, so a silhouette sweeping across the pixel reprojects along the surface that is actually moving over it.
• Neighbourhood clipping. The history is pulled toward the mean of the current frame's own neighbourhood, along the line between the two, only as far as it takes to enter the colour box that neighbourhood spans.
• Motion-weighted feedback. A long reprojection keeps less of the accumulation, which is what stops a fast object trailing behind itself.