JOGL (Java OpenGL) - Textures

@for Developers
@author Kai Ruhl
@since 2009-04

Textures the Classic Way

This article is an outsourced excerpt of my JOGL tutorial; it is concerned with textures. Instead of using the TextureRenderer, you can also use textures the classic way (i.e. as it is done in pure OpenGL). Doing so is split into the init() and the display() stage.

You need the following tools at your disposal:

• An int in an int[] (array) to store the texture id.
• A PNG image containing the texture.
• A GL object to operate on.

With that, go to the init stage:

1. have an int[] array for texture identifiers (1 int per texture)
2. load image data into a byteArray, but do not do anything with it yet
3. announce to OpenGL (GL) how many textures you want ever in this app:
   glGenTextures(<textureCount>, <fittinglySizedIntArray>);
4. per tex, announce to OpenGL what type it is:
   glBindTexture(GL_TEXTURE_2D, textureArray[<position>]);
5. per tex, load the image byteArray into graphics card (where texId == textureArray[<position>]):
   gl.glTexImage2D(<texId>, <always-0>,
                   <dataToUse: RGB, wid, hei, border>,
                   <dataSrc: RGB, UNSIGNED_BYTE, byteArray);
6. globally tell OpenGL what to do when zoom in (MAG) or zoom out (MIN):
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
7. globally tell OpenGL to enable 2D textures:
   glEnable(GL_TEXTURE_2D);

And in the display stage:

1. announce (before glBegin()) which texture you want to use:
   glBindTexture(GL_TEXTURE_2D, textureArray[<position>]);
2. draw only quads:
   glBegin(GL_QUADS);
3. for each quad, announce texture corner position before quad corner position:
   glTexCoord2f(0.0f, 0.0f);
   glVertex3f(-1.0f, -1.0f,  1.0f);

The above is certainly not a complete, tutorial-like description of how to use textures the native way. For details, may I refer you to the NeHe tutorial, which explains it much better. I hope this small excerpt persuaded you to use the JOGL TextureRenderer, as described in my JOGL tutorial. And with this, have a good time!

EOF (Apr:2009)