OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Arranging Texture Data

Suppose you have an external source of texture data—say an image editing program or another component of your application, perhaps written in another language or using another API over which you have no control. It is possible that the texture data is stored using a component order other than red, green, blue, alpha (RGBA). For example, ABGR is fairly common (i.e., RGBA bytes stored in little-endian order), as is ARGB and even RGBx (RGB data packed into a 32-bit word with one byte left unused). OpenGL is quite capable of consuming this data and making it appear as nicely formatted RGBA data to your shader. To do this, we use texture swizzle, which is a mechanism that allows you to rearrange the component order of texture ...