GLSL twin of gsplatVisibleMahalSq, shared by the visual and pick
vertex shaders (the TSL twin is gsplatQuadFootprintTSL in
shader-tsl.ts). Constants are interpolated from this module; the floor
is spelled 1e-4 exactly as the fragment discards spell it.
GLSL twin of gsplatVisibleMahalSq, shared by the visual and pick vertex shaders (the TSL twin is
gsplatQuadFootprintTSLinshader-tsl.ts). Constants are interpolated from this module; the floor is spelled1e-4exactly as the fragment discards spell it.