Using alpha values

[bonzovt]

How can I create a polygon that is semi transparent? I know that you can use glColor4f and that the last parameter is the alpha value with 1.0 being totally "solid." I have tried using this function but it isn't working. What else to I need to include to get the alpha values to work properly? Thanks!

[Deiussum]

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

[JD]

You can also put alpha channel in your texture then use DECAL env. mode. The texture color will get multiplied with texture alpha.

[bonzovt]

That helped, but now if I put in a value of say 0.3 for alpha, I have a flashing polygon instead of just a polygon that is 0.3 transparent. How do you get the flashing to stop?

[Deiussum]

You may be seeing z-buffer fighting. What do you use for your near and far clip planes? If the difference is too big, your z-buffer might not be able to differentiate between 2 polygons that are close to each other.

[deadalive]

Quick question does z-fighting occur gluOrtho2D projections?

[Deiussum]

Yes, it can. If for instance the difference between your near and far clip plane is 1,000,000,000 and you only have a z-buffer with 16-bits of precision, you are going to see a lot of z-fighting because a 16-bit number can only store 65,536 different values.