Biased sampling code

[Nielsbishere]

https://github.com/cschied/q2vkpt/blob/master/src/refresh/vkpt/shader/path_tracer.h#L464 shows the code:

vec2 pixel_offset = vec2(get_rng(RNG_PRIMARY_OFF_X), get_rng(RNG_PRIMARY_OFF_Y));
pixel_offset.x = sqrt(-2.0 * log(pixel_offset.x));
pixel_offset = clamp(pixel_offset, vec2(-1), vec2(1)) * 0.5;

and get_rng returns

return min(texelFetch(TEX_BLUE_NOISE, ivec3(p), 0).r, 0.9999999999999);

From this, we know that get_rng = [ 0, 0.9999999999999 ] (since the blue noise is unorm r16).
Therefore, pixel_offset would always be in range [ 0, 0.5 >, not [ -.5, .5 > which is required to sample all volume of the pixel (relative to the center 0.5,0.5 pixel).

As provided by this formula of the box muller transform, which always returns <0,1] when [0,1> are provided.
This means the .5,.5;1,1 area is the only part of the pixel that is traced.

Unless this is required for TAA for some reason, I'd imagine the pixel_offset needs to be:

vec2 pixel_offset = vec2(get_rng(RNG_PRIMARY_OFF_X), get_rng(RNG_PRIMARY_OFF_Y));
pixel_offset.x = min(sqrt(-2.0 * log(pixel_offset.x)), 0.9999999999999);
pixel_offset = pixel_offset - 0.5;