Resolution scaling & TAA

Resolution scaling

The compute shader can render at a reduced resolution to decrease the number of rays cast per frame. A configurable renderScale factor (0.25-1.0, default 0.5) multiplies the canvas dimensions to produce a smaller compute output texture. The blit pass then upscales this to the full canvas using bilinear filtering.

Canvas: 1920 × 1080
renderScale: 0.5
Compute texture: 960 × 540  (75% fewer pixels)
Blit: bilinear upscale back to 1920 × 1080

The depth texture remains at full resolution for geometry overlays (wireframe, axis). The scaled dimensions are passed into the shader as screenSize so that ray generation and thread dispatch use the correct coordinate space.

Temporal jitter and accumulation

Raymarching with fixed step offsets produces banding artifacts where iso-surfaces align with sample planes. Kiln addresses this in two stages:

Stochastic jitter: Each ray's starting offset is randomized per frame using the frame index as part of the seed:

let jitter = rand(rayToSeed(rayDir) + brickIter + uniforms.frameIndex);
t += jitter * stepSize;

This converts structured banding into high-frequency noise that varies every frame.

Temporal accumulation: A compute pass blends the current frame with a history buffer using an exponential moving average (EMA). Two ping-pong textures alternate as read and write targets to avoid read-write hazards:

let weight = 1.0 / (frameCount + 1);  // Progressive average
let blended = mix(history, current, weight);

On frame 0, weight = 1.0 shows the raw noisy frame. By frame 10, each pixel averages 11 samples, substantially reducing noise. Accumulation caps at 64 frames to avoid diminishing returns.

The accumulation resets automatically when:

• The camera moves (detected by comparing the view-projection matrix between frames)
• Rendering parameters change (render mode, transfer function, window/level, ISO threshold)

This gives immediate visual feedback during interaction, with progressive refinement when the view is still.