2D lighting - don't let light through the wall

I have a collision map, and some places that I want to be sources of light. A light source provides light, which is actually a form where I can see the earth. Now it looks like this:

So, light passes through the walls. I want to do this:

(I noted collisions with the walls in dark yellow)

Thus, the light rays stop when they meet the wall. I want to get the shape of the right light, the best thing would be a bitmap containing it)

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, allegro 4.2.1, 2- 0 1.

Thanx , .