OpenGL has a number of pre-defined types that should be available to various bindings. These are useful for ensuring cross-platform portability, since all platforms will use well-defined sizes for the parameters.
This table shows the C names for the types, as well as their bitdepth. OpenGL requires that these types have the exact bitdepth defined below. This also describes them and provides an enum for some of them. Many APIs, such as the pixel transfer and vertex format definition APIs, take enums that specify one of these types.
|C Type||Bitdepth||Description||Common Enum|
|GLboolean||1+||A boolean value, either GL_TRUE or GL_FALSE|
|GLbyte||8||Signed, 2's complement binary integer||GL_BYTE|
|GLubyte||8||Unsigned binary integer||GL_UNSIGNED_BYTE|
|GLshort||16||Signed, 2's complement binary integer||GL_SHORT|
|GLushort||16||Unsigned binary integer||GL_UNSIGNED_SHORT|
|GLint||32||Signed, 2's complement binary integer||GL_INT|
|GLuint||32||Unsigned binary integer||GL_UNSIGNED_INT|
|GLfixed||32||Signed, 2's complement 16.16 integer||GL_FIXED|
|GLint64||64||Signed, 2's complement binary integer|
|GLuint64||64||Unsigned binary integer|
|GLsizei||32||A non-negative binary integer, for sizes.|
|GLenum||32||An OpenGL enumerator value|
|GLintptr||ptrbits1||Signed, 2's complement binary integer|
|GLsizeiptr||ptrbits1||Non-negative binary integer size, for memory offsets and ranges|
|GLsync||ptrbits1||Sync Object handle|
|GLbitfield||32||A bitfield value|
|GLhalf||16||An IEEE-754 floating-point value||GL_HALF_FLOAT|
|GLfloat||32||An IEEE-754 floating-point value||GL_FLOAT|
|GLclampf||32||An IEEE-754 floating-point value, clamped to the range [0,1]|
|GLdouble||64||An IEEE-754 floating-point value||GL_DOUBLE|
|GLclampd||64||An IEEE-754 floating-point value, clamped to the range [0,1]|
1: ptrbits is the bitdepth of a CPU pointer address. Therefore, these types must be large enough to store a pointer: sizeof(void*).
Some of these types have the same internal representation as others. For example, a GLsizei is functionally equivalent to GLuint. However, the typename conveys a semantic meaning: GLsizei is used specifically for sizes of things. Similarly, GLclampf is just a GLfloat as far as C/C++ is concerned. However, when GLclampf appears in as a function argument, this means that the function will clamp this parameter to the [0,1] range. As a return type, it means the value won't exceed that range.