annotation occlusion

[nicolemarsaglia]

fix pseudocolor annotation depth against translucent volume rendering

[kmorel]

Thanks for taking on this fix, @nicolemarsaglia. This is a non-trivial fix.

It looks like the fix involves adding a secondary depth buffer that is used to determine whether to blend a fragment in front of or behind what is in the color buffer. Do we need this as a second depth buffer? Couldn't we just maintain the one depth buffer and do the behind blending if the color buffer is transparent or cull if it is opaque (which is what would happen with color blending anyway)?

[nicolemarsaglia]

Mmmm ya, I wasn't fully understanding the code and that max distance is our opaque geometry. I definitely made it more complicated than it needed to be.

I'm gonna take another swing at it. Thanks!