1

so I am stuck with the following problems about scenegraphs and translucent objects... My problem is that I want to render multiple translucent objects in one scene. I know that I have to render the opaque objects first and then the translucent from back to front. That is working well... More or less...

But the real problem is that I for example have one translucent cube, in white (or any other color) and with an alpha value for example of 0.5. The internal structure of the cube is given in an wavefront obj file and so the order of the single planes of the cube is given. I dont order the single planes of the object because that would be too much in a scene with >1000 objects and >1000 vertices of each object, so i only order the objects as whole. If i render the single planes of the object and move around, there comes the moment, when one plane which is nearer than another one is rendered before that other one. And then the second one is not being rendered because the depth buffer is not allowing this, which is an error in the rendering.

Shutting down the depth buffer is not a solution: I need it because there may be complex objects which are translucent and opaque.

Any hints how i can achieve that the objects, even if they are complex and both opaque and translucent, are rendered in a correct way ?

genpfault
  • 51,148
  • 11
  • 85
  • 139
kke
  • 353
  • 2
  • 8

1 Answers1

3

Basically you have to do the following:

  • Separate everything into opaque and translucent (if one object consists of both you have to tear it appart)

  • Clear depth buffer

  • Enable Depth Test and draw everything opaque.

  • make depth buffer read only: glDepthMask(GL_FALSE)

  • draw everything translucent back to front.

That should do the trick.

D-rk
  • 5,513
  • 1
  • 37
  • 55
  • Ok, but the problem is, "back to front" means i have to order it. This ordering has to be on every triangle, because of the scenario presented above. But this could be too much. Is there any way, doing it with a shader ? – kke Apr 05 '13 at 12:04
  • No, it cannot be done with a shader since it processes triangles independently. Rendering translucent objects accurately is hard to do. Even if you sort every triangle you can have errors because of intersecting triangles and so on. Can't you live with the error made when sorting on object level? you have to find a compromise between speed and accuracy here. – D-rk Apr 05 '13 at 12:26