Respect hell and hellfire color maps for fully lit and fully dark tiles

[obligaron]

Fixes #6535

Background

• The renderer has a optimization for fully lit and fully dark tiles.
  • For fully lit tiles (light table index 0) the color map is ignored and a simple copy of the pixels is made
  • For fully dark tiles (light table index 15) the color map is ignored and all pixels are filled with black.
• This optimization assumes that the color map always maps to the same color (fully lit) or maps always maps to black (fully dark). This is not true.
  • Hell levels have a color map for fully lit tiles to support the ceiling animation.
  • Hellfire levels there do not have a fully dark color map.
• In [Issue Report]: Flickering graphics issue walking underneath animated ceiling tiles #6535 one ceiling tile has a dLight value of 0 (fully lit).
  • This happens more often in devilutionX, because the light is updated more often since b7424a0.
  • The bug is more visible when + light radius items are equipped.

Changes

• Added a helper (IsFullyDark/IsFullyLit) to check if the optimization can be used.
• Don't use incompatible optimizations for the affected levels.
• Added an assert to check if the optimizations are correctly enabled/disabled.

Notes

• We can change the way hellfire levels are handled. Currently they mostly use the color 1 for completely dark tiles. We could change this to pure black (0) and still use the optimization.

[glebm]

Can you please add a comment about what these asserts are testing

[obligaron]

I opened #7168 for it 🙂

[AJenbo]

I didn't think that was actually solvable as I though it was related to the pixels which where incorrectly encoded in the tiles. Nice work :)

[AJenbo]

@glebm oh, sorry I see I overlapped with your comment/review

[obligaron]

I didn't think that was actually solvable as I though it was related to the pixels which where incorrectly encoded in the tiles. Nice work :)

That was my first impression too, but then I discovered that the older version didn't have this problem. And so my chase down the rabbit hole began. 😁