GlActiveTexture

glActiveTexture is a function in the OpenGL graphics API used to select which texture unit subsequent texture-related operations will affect. A texture unit is a distinct location within the graphics hardware that can hold a texture. Modern GPUs have multiple texture units, allowing for the use of several textures simultaneously in a single rendering pass.

When you call glActiveTexture, you specify a texture unit index. For example, glActiveTexture(GL_TEXTURE0) selects the first texture unit, glActiveTexture(GL_TEXTURE1) selects the second, and so on. After calling glActiveTexture, any subsequent calls to functions like glBindTexture, glUniform1i (for texture samplers), or texture environment settings will apply to the currently active texture unit. This is crucial for managing multiple textures, such as diffuse maps, normal maps, and specular maps, in complex shader programs. Without glActiveTexture, all texture operations would default to a single texture unit, limiting the visual complexity achievable. It's a fundamental part of texture management in OpenGL.