GLDIFFUSE

GLDIFFUSE is a term used in computer graphics to denote the diffuse component of a surface’s reflectance in lighting calculations. In OpenGL contexts, it is commonly associated with the GL_DIFFUSE material property, which defines how much diffuse light a surface reflects.

In the OpenGL fixed-function pipeline, the diffuse color is set with functions such as glMaterialfv and the parameter GL_DIFFUSE. This diffuse term contributes to the overall lighting by describing how a surface scatters light in many directions, typically producing a matte appearance. In modern shader-based rendering, the diffuse contribution is implemented directly in the shader as a product of the material’s diffuse color, the light’s diffuse intensity, and the Lambertian factor max(0.0, dot(normal, lightDir)).

The diffuse component is generally isotropic, meaning it is roughly the same in all viewing directions and primarily depends on the angle between the surface normal and the light direction. It is distinct from the specular component, which accounts for shiny highlights that vary with the viewer’s position and surface roughness, and from ambient lighting, which provides a baseline illumination independent of light direction.

GLDIFFUSE, when used, refers to the diffuse reflectance property of a material. While the exact naming can vary by API or documentation, the underlying concept remains the same: it governs how a surface diffusely reflects incoming light. See also GL_DIFFUSE, GL_AMBIENT, and GL_SPECULAR for related lighting properties.