object render overlaying

Game Engine Game Engine Support and Discussion
1

Is it possible to setup an object to be rendered after all other objects in a scene,
so that rendering this object can access scene z-buffer from attached glsl shader?

2

Depends on what you are trying to do. If you are trying to do a 2D filter then there is an actuator that does this specifically. I’m not sure if there is a good way to force the rendering order for objects. I’m sure the BGE does at least a few tricks with the render order depending on the scene layout. At the very least you have to render in the correct order to get transparency to work correctly.

3

The 2D filter is not exactly what i need.
I need some varying and uniforms to pass.

And this code does not work either:

uniform sampler2D bgl_DepthTexture;
void main(void)
{
  gl_FragColor = texture2D(bgl_DepthTexture, gl_TexCoord[0].st);
}
4

Try searching in the BGE resources forum for SSAO ( Screen space ambient occlusion). If memory serves, that is a glsl filter that uses the depth buffer. You should be able to use it to figure out how to get it for your filter.