Opengl alpha blending

Question

0.00/5 (No votes)

See more:

I'm trying to create a small solar system and render it uding opengl. I got several spheres rotating around origo with planetary textures on them.

One of the planets got an atmosphere created by creating a slightly larger sphere at the same position with a texture with alpha blending.

Everything works except when the watched from a distanace it looks like black riples in the atmosphere. It's only when watched froma distance. When up close it's working perfectly.

C#

void drawAtmo()
{
    glEnable(GL_BLEND);
    glBlendFunc(GL_ONE, GL_ONE);
    glPushMatrix();
    glEnable(GL_CULL_FACE);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_TEXTURE_2D);
    glColor4f(1, 1, 1 ,0.5);
    glBindTexture(GL_TEXTURE_2D, shared.earthTexture1);
    gluSphere(shared.quadric, 3.2, 32, 32);
glPopMatrix();
glDisable(GL_BLEND);
}

Posted 26-Oct-10 12:43pm

Psilobe

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Anthony Mushrow · Accepted Answer · 2010-10-26T16:15:00

It's likely caused because your using a 16-bit depth buffer, which means that from a distance there isn't enough detail in the depth buffer to differentiate between the planet and its atmosphere so they're being drawn a little randomly.

I'd like to mention that the depth buffer doesn't store depth information with the same degree of accuracy across the whole scene, objects near the screen will have more precision than those towards the back of scene.

The solution is to either use a 24-bit depth buffer, or adjust your zNear and zFar values to squeeze some more precision out of the depth buffer, so it's a pretty simple fix. If your already using a 24-bit depth buffer then you should adjust your near and far values, change z-near so it is not as close to 0 and reduce the distance between zNear and zFar

OpenGL FAQ on the depth buffer[^]