glVertexAttrib4f0

glVertexAttrib4f is an OpenGL function used to specify a constant value for a generic vertex attribute. Its purpose is to set the current attribute value for a given attribute index, so that the shader can read a fixed vector when per-vertex data is not supplied.

The standard signature is glVertexAttrib4f(index, x, y, z, w), where index is the generic attribute location (an unsigned integer), and x, y, z, w are floating-point components. The function defines a four-component vector that becomes the constant value for the specified attribute.

When a vertex attribute array is enabled for the given index (via glEnableVertexAttribArray), vertex attribute data is normally sourced per vertex from a bound array through glVertexAttribPointer. In that case, glVertexAttrib4f provides a constant value only if the attribute array is disabled for that index. If the array remains enabled, the per-vertex data overrides the constant value from glVertexAttrib4f.

Common use cases include supplying a fixed attribute to shaders, such as a constant color, normal, or other attribute that does not vary per vertex, or providing a default value when a buffer is not bound. It is also used in conjunction with instanced rendering or when a shader expects a specific attribute that is not provided by a vertex buffer.

Note that there is no standard function named glVertexAttrib4f0; the correct form to set a constant attribute at location 0 is glVertexAttrib4f(0, x, y, z, w). In GLSL, attribute locations can be bound explicitly or queried after program linking.