ARBvertexprogram

ARBvertexprogram is a set of assembly-like instructions used in OpenGL for programming the vertex processing stage of the graphics pipeline. This allows developers to perform custom calculations on vertex data, such as transforming vertices, calculating lighting, and generating per-vertex attributes that can be passed to the fragment shader. It provides a lower-level control over vertex transformations compared to fixed-function pipeline operations.

These programs are written in a specific assembly language defined by the OpenGL ARB (Architecture Review Board). The instructions operate on registers, which store various types of data like vertex coordinates, normals, texture coordinates, and color values. A vertex program typically takes vertex attributes as input, manipulates them using arithmetic and vector operations, and outputs transformed vertex positions and other varying variables.

The primary purpose of ARB vertex programs was to enable more sophisticated visual effects and optimizations that were not possible with the standard fixed-function OpenGL pipeline. This includes features like complex procedural texturing, custom animation effects directly on vertices, and more advanced lighting models. While modern OpenGL offers more powerful shading languages like GLSL, ARB vertex programs were a significant step towards programmable graphics and laid the groundwork for future shader development. They are still supported for backward compatibility in many OpenGL implementations.