vol_composite

Post-process pass that puts the demo's emissive volumes on screen. preseed.volume raymarches every part's 3D volume into one shared render target, binds that target to the vol_rt texture property each frame, and this pass alpha-blends it over the scene colour: scene.rgb * (1 - v.a) + v.rgb. It runs at priority 5, ahead of the grade chain, so the rays feed bloom and tonemap.