Cast shadow in Unity

Hi, as you know Unity free doesn’t support shadow part. So I want to render the viewTexture again in C# to add shadow. I have thought about a way using RayTracing, which means casting a ray from each pixel (Raycast(ScreenToPoing)) to see if it hits anything and the ray from hitPoint to light source will hit anything. And then render the whole viewTexture again. (I just test those Objects which are static and will never move in the game)

The result is good but it seems too much computation. Is anyone here has better method?

Thanks in advance.

update your version of unity? or check this link

I heard about stencil shadow now accessible in unity free with the stencil buffer.

But maybe it’s possible to optimise your raycast system.
Decrease the number of raycast then create polygon that cover the place
where must be shadow and use a gradiant shader to smooth the result ??