title: I need to do OpenGL texturing with certain color transparent
body: <p>Still, I am using OpenGL 1.x;
   I could blit a 24bit targa image in OpenGL. Let's say I got a targa file with a monster on it.
  its background is blue. How could I dicard this blue information?</p>
  
  <p>An alternative: I know lesson32 in NeHe tutorial used a 32bit targa, Yeah, I could display it in my application. Here a new problem arises: How could I create 32bit TGA with certain area transparent. I don't get the point of the NeHe explanation.</p>
  
  <p>here is my way in photoshop which does not work:</p>
  
  <ol>
  <li>Create a new file, put the
  background layer into the trash and
  create a transparent layer.</li>
  <li>Create a selection on the
  transparent layer and fill it with
  some solid color,say ,red.</li>
  <li>Save the file as a 32bit TGA and
  blit in my OpenGL app.</li>
  </ol>
  
  <p>To my dismay, the region I thought should have been transparent is now pure white...
  (the image loading method has no problem, as it can load some other good 32bit targas)</p>