Vertex Format

Cited Officialhttps://www.opengl.org/wiki/Vertex_Specification

Vertex Format

The glVertexAttribPointer​ functions state where an attribute index gets its array data from. But it also defines how OpenGL should interpret that data. Thus, these functions conceptually do two things: set the buffer object information on where the data comes from and define the format of that data.

The format parameters describe how to interpret a single vertex of information from the array. Vertex Attributes in the Vertex Shader can be declared as a floating-point GLSL type (such as float​ or vec4​), an integral type (such as uint​ or ivec3​), or a double-precision type (such as double​ or dvec4​). Double-precision attributes are only available in OpenGL 4.1 or ARB_vertex_attrib_64bit.

The general type of attribute used in the vertex shader must match the general type provided by the attribute array. This is governed by which glVertexAttribPointer​ function you use. For floating-point attributes, you must use glVertexAttribPointer​. For integer (both signed and unsigned), you must use glVertexAttribIPointer​. And for double-precision attributes, where available, you must useglVertexAttribLPointer​.

Each attribute index represents a vector of some type, from 1 to 4 components in length. The size​ parameter of the glVertexAttribPointer​ functions defines the number of components in the vector provided by the attribute array. It can be any number 1-4. Note that size​ does not have to exactly match the size used by the vertex shader. If the vertex shader has fewer components than the attribute provides, then the extras are ignored. If the vertex shader has more components than the array provides, the extras are given values from the vector (0, 0, 0, 1) for the missing XYZW components.

The latter is not true for double-precision inputs (OpenGL 4.1 or ARB_vertex_attrib_64bit). If the shader attribute has more components than the provided value, the extra components will have undefined values.

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