Mipmapping Equirectangular

Hi there,

I want to manually compute mipmaps for an equirectangular texture. 

I wrote a compute shader that loads first mip level into LDS using bilinear sampling. Then I'm applying a simple box filtering (using parallel prefix reduction) to output each mip levels.

The above shader was already tested for regular 2d textures.

I noticed however a discontinuity on higher mip levels, exactly where the u axis wraps around, even if I'm loading the LDS using a wrap filtering mode or forcing fract operation for uv coordinates - I can't seem to get rid of the artifact …