How to draw from the inside of the light geometry in deferred shading

Question

I\'m trying to implement a deferred shader with OpenGL and GLSL and I\'m having trouble with the light geometry. These are the steps I\'m taking:

Bind multit         


        

Answer 1

If i remember correctly, in my deferred renderer i just render only the backfaces of the light volume. The drawback is you cannot depth test, you will only know if a light is behind a geometry after the light calculation is done and discard the pixel. As another answer explained, you can do depth testing. Test for greater or equal to see if the backface is behind or on a geometry, therefore intersects with the surface of the geometry.

Alternatively you could check if you are inside the light volume when rendering and switch front faces accordingly.

Answer 2

well in my case, i do it like that:

Bind gbuffer framebuffer
Render color, position, normal
Unbind framebuffer

Enable blend
Enable depth testing

glDepthMask(0);
glCullFace(GL_FRONT);   //to render only backfaces
glDepthFunc(GL_GEQUAL); //to test if light fragment is "behind geometry", or it shouldn't affect it
Bind light framebuffer
Blit depth from gbuffer to light framebuffer //so you can depth-test light volumes against geometry
Render every light