GLsizei

GLsizei is a signed integer type defined by the OpenGL API for use as a parameter representing counts and sizes in various functions. In OpenGL headers, it is typically defined as a standard signed int (for example, typedef int GLsizei;), which in practice is a 32-bit signed value on most desktop implementations. The exact width can be platform-dependent, but GLsizei is intended to be large enough to express practical counts and dimensions used in graphics operations.

GLsizei is used in many API calls to specify quantities such as the number of vertices, width and height of images, or the number of elements to process. Because it is signed, negative values are invalid for these uses, and calls may generate errors such as GL_INVALID_VALUE if a negative count or dimension is supplied. Functions that accept dimension or count parameters—such as glViewport, glScissor, glDrawArrays, glDrawElements, and glTexImage2D—often use GLsizei for those parameters. It is distinct from related unsigned types (for example, GLuint) and from GLsizeiptr, which is used for sizes in bytes and is defined as a pointer-sized signed type.

In code, GLsizei is typically assigned from regular integers when representing counts, with the expectation that the value is non-negative and within the limits of the underlying implementation or buffers. When portability is a concern, developers should rely on the API and error checks rather than assuming a particular bit width.

See also: GLint, GLuint, GLsizeiptr.