Temporal anti-aliasing (TAA)

Thin wires and a checker floor shimmer at 1 sample per pixel. TAA shifts the camera by under a pixel every frame and blends each frame with the last.

The problem

A pixel takes one sample. Anything thinner than a pixel, like a power line or a lattice brace, pops in and out as the camera moves. MSAA takes extra samples on triangle edges, but a pattern drawn inside a shader (the checker floor here) still shimmers. Supersampling fixes both, at several times the cost of every frame.

How it works

The source (a Unity URP renderer feature) spreads the extra samples over time:

1. Jitter: each frame the projection is offset by a Halton (2,3) point, 8 points in a loop, up to half a pixel each way.
2. Reproject: read the depth, rebuild the pixel's view position with the un-jittered inverse projection, and project it with last frame's view-projection. That gives where this pixel was in the history.
3. Clamp: take the min and max colour of the 3x3 neighbourhood in the current frame and clamp the history colour into that box.
4. Blend: 95% history, 5% new frame. The history weight drops with camera motion: exp(-100 x screen distance moved).
5. Ping-pong two history buffers.

What I hit

The reprojection uses depth and camera motion only; there are no per-object motion vectors. A box moving on its own reads the wrong history. With the clamp off it leaves a long orange trail and is barely visible itself. With the clamp on the trail is mostly gone: the old colour falls outside the 3x3 range and gets pulled back.

The history starts empty, so the first frames would fade in from black. I seed a new history from the current frame.

My build

three.js (r187), WebGL2. Each panel is the same 640 x 1080 slice of one 1920 x 1080 view, so all three show the same view at the same scale. MSAA is a 4-sample render target. TAA history is two half-float targets per panel.

Scene: five lattice pylons 26 m tall with 5 cm braces, four power lines 5 cm thick, a 70-slat fence, and a checker floor with no texture filtering.

Trade-offs

• Smooths edges and shader aliasing alike, for one extra full-screen pass
• Converges on a still image toward a supersampled look
• Soft image: the history blend blurs fine detail
• Ghosting on anything the reprojection can't follow; the clamp hides most of it
• Fast camera moves cut the history weight, so some shimmer returns in motion
• I rendered on a software GPU, so no timings

When to use it

Scenes full of thin geometry, foliage or noisy shading where MSAA leaves shimmer. Add motion vectors before relying on it for fast-moving objects.