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The glViewport function sets the viewport.

void glViewport(
  GLint x,
  GLint y,
  GLsizei width,
  GLsizei height


x, y
The lower-left corner of the viewport rectangle, in pixels. The default is (0,0).
width, height
The width and height, respectively, of the viewport. When an OpenGL context is first attached to a window, width and height are set to the dimensions of that window.


The glViewport function specifies the affine transformation of x and y from normalized device coordinates to window coordinates. Let (xnd, ynd) be normalized device coordinates. The window coordinates (xw, yw) are then computed as follows:

Viewport width and height are silently clamped to a range that depends on the implementation. This range is queried by calling glGet with argument GL_MAX_VIEWPORT_DIMS.

The following functions retrieve information related to glViewport:

glGet with argument GL_VIEWPORT

glGet with argument GL_MAX_VIEWPORT_DIMS

Error Codes

The following are the error codes generated and their conditions.

Error code Condition
GL_INVALID_VALUE Either width or height was negative.
GL_INVALID_OPERATION glViewport was called between a call to glBegin and the corresponding call to glEnd.


  Windows NT/2000: Requires Windows NT 3.5 or later.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in Gl.h.
  Library: Use Opengl32.lib.

See Also

glBegin, glDepthRange


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