emission_raymarch

Marches an emissive 3D volume into a 2D storage target, one invocation per pixel. The volume's RGB is emission and its alpha is density; the output is premultiplied vec4(scatter, 1 - transmittance), which the demo's composite post-process blends over the scene. The frame's depth blit clips each ray at opaque geometry within occluder_range, so a surface in front of the volume hides it.

preseed/volume.module owns this shader: it allocates the U uniform run, packs the camera's inverse view-projection and the volume's world AABB into it, and dispatches once per volume per frame.