6.21.4 Spectral Synthesis

Now that we can create a single frequency noise function using the framebuffer, we need to create the different octaves and to composite them into one texture. For each octave:

1.

Scale the texture matrix by a power of 2 in both s and t.

2.

Translate the texture matrix by a random offset in both s and t.

3.

Set the texture wrap mode to GL_REPEAT for s and t.

4.

Draw a textured rectangle.

5.

Accumulate the color buffer contents.

The random translation is an attempt to minimize the amount of overlap between each octave's texels; without it, every octave would use texels from the same corner of the input image. The accumulation is typically done with a scale factor that controls the weight we want to give each octave.