How to deal with the concave-convex TV background wall with white decoration style

1. fills the concave square. 2. The color is gray. 3. Then adjust the angle.

First, a scheme is given. Fill in the penultimate debugging angle of 270 in the second line from the left, and you will understand (choose your own scheme. If you really feel that the color can't achieve the expected effect, add it with PS later). That's H. If you are proficient in CAD, you don't need to explain it.