blending

Provide an alpha channel and use (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) as blending factors.

-Lev

Edit: spelling

[edited by - Lev Povalahev on December 30, 2003 7:59:58 AM]

Either use a format which supports an alpha channel or write a function to convert your rgb image into a rgba image with black parts having a 0 alpha channel value.

Here is some code,
r,g,b define the colour you want filtered out. *in is a pointer to your rgb image data while out is a pointer to your rgba array.

void ColorKey(GLubyte *in,GLubyte *out,GLubyte r,GLubyte g,GLubyte b,
	      unsigned int width,unsigned int height) {
  unsigned int i,j;
  for(i=0;i<height;++i)
    for(j=0;j<width;++j) {
      out[4*(i*width+j)+0]=in[3*(i*width+j)+0];
      out[4*(i*width+j)+1]=in[3*(i*width+j)+1];
      out[4*(i*width+j)+2]=in[3*(i*width+j)+2];
      if(r==in[3*(i*width+j)+0] &&
	 g==in[3*(i*width+j)+1] &&
	 b==in[3*(i*width+j)+2])
	out[4*(i*width+j)+3]=0;
      else
	out[4*(i*width+j)+3]=255;
    }
}

In your init code set the function to draw anything that has above 0 alpha value.

glAlphaFunc(GL_GREATER, 0.0f);


Once you have your texture, use this to not draw alpha values 0.

glEnable(GL_ALPHA_TEST);
//draw your stuff here
glDisable(GL_ALPHA_TEST);//remember to disable it again