OpenGL Programming Guide

Appendix AOrder of Operations

Fragment Operations

If texturing is enabled, a texel is generated from texture memory for each fragment and applied to the fragment. Then fog calculations are performed, if they're enabled, followed by coverage (antialiasing) calculations if antialiasing is enabled.

Next comes scissoring, followed by the alpha test (in RGBA mode only), the stencil test, the depth-buffer test, and dithering. All of these operations can be disabled. Next, if in index mode, a logical operation is applied if one has been specified. If in RGBA mode, blending is performed.

The fragment is then masked by a color mask or an index mask, depending on the mode, and drawn into the appropriate buffer. If fragments are being written into the stencil or depth buffer, masking occurs after the stencil and depth tests, and the results are drawn into the framebuffer without performing the blending, dithering, or logical operation.

OpenGL Programming Guide