Spatial tiling for interactivity
Added: -compute shaders to handle spectral conversion and splatting, one for RGb and one for spectral. The same fragment shader is used to display the result for both rgb and spectral. -spatial subdivision when launching rays. When active, only one every X rays is shot. The amount varies according to the FPS.
To test: check the "optimize FPS" box in interactive mode, then choose your target FPS (currently 10 to 60). Subdivision goes up to 1 every 9 rays/pixel.