Implementation of fade to black effects from a popular game about fighting animals.
A horizontal line starts rotating to the left while turning the screen dark.
Rotates a pixelated copy of the fragment's UV coordinates using the _Angle parameter, this is the rotated line that "turns the screen dark".
Then fragments become black if either:
- They are above the horizontal line and and below the rotated line.
or
- They are below the horizontal line and and above the rotated line.
Screen turns dark horizontally, odd lines start from the left and even lines from the right.
Fragments turn dark when progress (from o to 1) is higher than their uv.x. We flip the even fragment's uv.x to make them turn black from right to left.