The first example

The first example program gives an example of rendering to 2 textures, one after each other, and then applying those textures to another cube. The code is based on the same example as used in the first article; there are some minor changes however.

Firstly, in the FBO setup code in the init function we create and bind a second texture to the FBO we created. Notice how we bind it to different attachment point to the first texture by using GL_COLOR_ATTACHMENT1_EXT as the bind point.

The rendering for the scene is basically the same as well, however instead of drawing the cube with its colours on once we draw it twice, the second time with the colours at half the intensity.

You should notice in the example program that when we render to the FBO we explicitly tell OpenGL to render to GL_COLOR_ATTACHMENT0_EXT and then GL_COLOR_ATTACHMENT1_EXT; this is because the FBO remembers the last buffer you told it to draw to, so when the drawing loop runs for the second time the first texture isn’t updated as the drawing goes to the destination given in the last glDrawBuffer() call, which in this case is GL_COLOR_ATTACHMENT1_EXT. To see this effect comment out line 133, which has the glDrawBuffer() call in it, and you will notice the texture on the left hand cube is never updated.

Multiple Render Targets