viewing translucent polygons from behind (color is too dark)

OpenGL Development JOGL Development
#1

I’ve been messing around for several hours trying to get a simple translucent polygon to look correct from both sides. It’s fine from the front, and blending works as expected. In fact if I put several in a row the ‘add’ correctly. If I move the camera around to the back and look toward the light source through the polygons they are dark for obvious reasons.

So, how might I convince the polygon to behave as you would expect a pane of glass to behave in a window? It seems as long as I have lighting enabled when I draw the poly it will never look right, but if lighting is off you cant see it at all…

I can put some code up if needed, and thanks for any input.

Keith

#2

glLightModeli( GL.GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE );

I don’t know if that will work for you or not.

#3

That was one of the things I tried, unfortunately. It supplied a partial fix by at least allowing you to SEE the poly from the back, but then the lighting was too dark because, of course, the light source was shining on the front face. I’m imagining a stained glass window with the sun shining on it… it’s well lit from the front AND back.

#4

I think you are trying to accomplish something quite complex, translucency with correct lighting from the back is incredibly computationally expensive, and is only quite recently implemented in the renderers of 3D Modeling apps, such as 3D Studio Max, Blender, Maya, etc. Corrct me somebody if I’m wrong, but I don’t think there’s any way OpenGL can give you this effect (the physically correct calculation of photons as they pass through a translucent surface) “for free” - I imagine you’d have to simulate it with more lights on the other side of the glass, or by tweaking the material.

Dawid