Problem with triangles intersection with alpha.

OpenGL Development JOGL Development
#1

Hello!

I would like to draw triangles (with the same Y - up direction - value), which ones may intersect each other. When I draw it with alpha value, I see darker blobs.
How can I resolve it?
screenshot:: http://delfin.unideb.hu/~fazekaim/problem.jpg

I have a plane quad (in red colors), and above the quad a lot of randomly generated triangles with the same Y(up direction) value.

Thanks.

#2

You enabed blending with gl.glEnable(GL_BLEND) ?
If so, you could alter the blend function so it’s not additive. Some call to gl.glBlendFunc(…, …)

(I’m not sure, I’m quoting from memory. Maybe I’m misunderstanding your problem.)

#3

I’m using this:

gl.glEnable(GL.GL_BLEND);
gl.glColor4f( 0.0f, 0.0f, 0.0f, 0.3f );
gl.glBlendFunc(GL.GL_SRC_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA);

Should I use other blend funt.?

#4

Yes.
In case you don’t want to alpha-sum at all, you could just disable blending (which is the default).
What behaviour should your lines have, when they’re drawn?

#5

But, if the blending isn’t enabled, the triangles arn’t transparent.
I would like to draw the triangles with 0.3 alpha value without the additive effect.
Or may I’m wrong?

#6

If you try to overlap many polygons with the same depth you will have to use GL_POLYGON_OFFSET i think.