1

I have two functions that I want to combine the results of:

drawAmbient
drawDirectional

They each work fine individually, drawing the scene with the ambient light only, or the directional light only. I want to show both the ambient and directional light but am having a bit of trouble. I try this:

[self drawAmbient];

glEnable(GL_BLEND);
glBlendEquation(GL_FUNC_ADD);
glBlendFunc(GL_ONE, GL_ONE);

[self drawDirectional];

glDisable(GL_BLEND);

but I only see the results from first draw. I calculate the depth in the same way for both sets of draw calls. I could always just render to texture and blend the textures, but that seems redundant. Is there I way that I can add the lighting together when rendering to the default framebuffer?

Nicol Bolas
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Curyous
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  • How do you do the lighting? In this case, what most likely happens is that depth testing is enabled and your 2nd run fragments are all discarded. – KillianDS Aug 07 '12 at 05:51
  • +1 that's what I was typing when your comment appeared :-) – Kos Aug 07 '12 at 05:51
  • If I disable depth testing, though, the scene won't be drawn properly in the 2nd lot of draw calls in drawDirectional. – Curyous Aug 07 '12 at 06:32
  • You can add z-bias (through projection matrix if there is no separate value in OpenGL ES) for second render pass. It's not accurate solution, but should solve depth-test problem. – brigadir Aug 07 '12 at 08:05
  • @KillianDS Why not make this an answer (but too late now anyway ;))? – Christian Rau Aug 07 '12 at 08:26
  • @brigadir Just configuring the depth test correctly is much more accurate. – Christian Rau Aug 07 '12 at 08:26

2 Answers2

3

You say you calculate the depth the same way in both passes. This is of course correct, but as the default depth comparison function is GL_LESS, nothing will actually be rendered in the second pass, since the depth is never less than what is currently in the depth buffer.

So for the second pass just change the depth test to

glDepthFunc(GL_EQUAL);

and then back to

glDepthFunc(GL_LESS);

Or you may also set it to GL_LEQUAL for the whole runtime to cover both cases.

Christian Rau
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0

As far as I know, you should render lighting to separate render targets and then combine them. So you will have rendered scene into these targets:

  • textured without lighting
  • summary diffuse lighting (fill with ambient color and additively render all light sources)
  • summary specular lighting (if you use specular component)

Then combine textures, so final_color = textured * diffuse + specular.

brigadir
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  • Why on earth should separate render targets be neccessary when he just wants to add the individual images, which can be done by simple blending. – Christian Rau Aug 07 '12 at 08:21