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

Vertex Shading

For each vertex that is issued by a drawing command, a vertex shader will be called to process the data associated with that vertex. Depending on whether any other pre-rasterization shaders are active, vertex shaders may be very simple, perhaps just copying data to pass it through this shading stage—what we’ll call a pass-through shader—to a very complex shader that’s performing many computations to potentially compute the vertex’s screen position (usually using transformation matrices, described in Chapter 5), determining the vertex’s color using lighting computations described in Chapter 7, or any multitude of other techniques.

Typically, an application of any complexity will have multiple vertex shaders, but only one can be ...