glDrawBuffers

glDrawBuffers is a function in the OpenGL (Open Graphics Library) API used to control which of the active fragment shaders outputs are written to the currently bound framebuffer's color buffers. This function is particularly useful in advanced rendering techniques such as deferred shading, multi-pass rendering, and the use of multiple render targets (MRTs).

When a fragment shader executes, it can produce multiple output values, often referred to as varying variables. These outputs are intended to be written to different locations within the framebuffer. By default, a fragment shader typically outputs to a single color buffer. However, glDrawBuffers allows developers to specify an array of buffers to which each fragment shader output should be directed.

The function takes two arguments: the number of buffers to enable, and a pointer to an array of constants that specify the target buffer for each output. These constants, such as GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, and GL_NONE, indicate which color buffer index the corresponding fragment shader output should be written to. For example, if a shader has two output variables, one might be directed to GL_COLOR_ATTACHMENT0 and the other to GL_COLOR_ATTACHMENT1. Using GL_NONE for a particular output indicates that it should not be written to any color buffer.

This capability is essential for rendering complex scenes where multiple pieces of information, such as color, normals, and depth, need to be rendered to separate textures in a single rendering pass. This can significantly improve rendering performance by reducing the number of times geometry needs to be processed.