glViewport.3G man page

glViewport — set the viewport

C Specification

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


x, y

Specify the lower left corner of the viewport rectangle, in pixels. The initial value is (0,0).

width, height

Specify the width and height of the viewport. When a GL context is first attached to a window, width and height are set to the dimensions of that window.


glViewport specifies the affine transformation of x and y from normalized device coordinates to window coordinates. Let x nd y nd be normalized device coordinates. Then the window coordinates x w y w are computed as follows:

x w = x nd + 1 ⁢ width 2 + x

y w = y nd + 1 ⁢ height 2 + y

Viewport width and height are silently clamped to a range that depends on the implementation. To query this range, call glGet() with argument GL_MAX_VIEWPORT_DIMS.


GL_INVALID_VALUE is generated if either width or height is negative.

Associated Gets

glGet() with argument GL_VIEWPORT

glGet() with argument GL_MAX_VIEWPORT_DIMS

See Also