How can I create 2D shadows that let me detect when the player is inside them?

Question

I'm working on a 2D platform game, and I want my platforms to cast shadows along with some way to detect if the player is inside the shadow area (that is, not hit by the sun).

More specifically: I have a character, some platforms and a sun. When the player is under the shadow of some platform he is safe. If he goes to a location when the sunlight hit him, then he starts losing heath until he enters other shadow spot.

Right now the shadows are boxes with a transparent/diffuse material. Boxes are good because I can determine when the player enters or leaves them, but they are are ugly and don't have any animation. I need a shadow that changes when the sun changes its position, without losing the ability to determine when the player is inside a shadow (I think this can be done using a ray cast)?

How can I accomplish this?

Answer 1

I did a quick sketch of how it could be done.

Yellow round thing is the Sun, obviously, grey things are rays and black ones are boxes. The blue lines are the shadow triangles and yellow dots are the vertex points.

You cast rays down from the Sun to the edges of the blocks and through them. Take the vertices where it hit the box and the ground. Then you draw the mesh in code.