In this case, masking. But first, you have to make an opening in the wall shape. I copied the points in the "hueco" layer, and copied them into the "pared_izq" layer, making sure that the points were all
inside the points for the wall. Then I deleted the Shape already on the "pared_izq" layer. Select all the points on the layer ( the 4 points for the wall, and the 4 points for the doorway just a little inside the wall, and create a new shape with the same settings as the old wall shape. This will make a new shape of the wall with a hole in it that you can see through.
The you have to make the mask. I made a copy of the "pared_izq" layer and deleted all the points. This was so I had a new layer in the the same place in 3D slpace as the wall. Then I drew a rectangle that covered the wall from top to bottom and started at the side of the doorway closest to the camera and going to the front of the room.
I set up the masking my setting all layers to "don't mask thid layer" except:
1. the group (cube) layer, to "Mask On - Reveal All"
2.The "pared_izq mask" layer, to "Subtract from mas, this layer will be invisible.
4. The character, to "Mask this layer"
I put in a character. I was bored. I also played with the "techo" layer so it had fills. I played with some of the 3D camera bits, and found that I had to adjust the Origin point of some layers or some part would disappear behind others when you moved position.
Here is the file
HERE
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