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

Application Setup

For our procedural bump map shader to work properly, the application must send a vertex position, a surface normal, and a tangent vector in the plane of the surface being rendered. The application passes the tangent vector as a generic vertex attribute and binds the index of the generic attribute to be used to the vertex shader variable tangent by calling glBindAttribLocation(). The application is also responsible for providing values for the uniform variables LightPosition, SurfaceColor, BumpDensity, BumpSize, and SpecularFactor.

You must be careful to orient the tangent vectors consistently between vertices; otherwise, the transformation into surface-local coordinates will be inconsistent, and the lighting computation will ...