glViewport specifies the affine transformation of x and y from normalized device coordinates to window coordinates. Let (xnd,ynd) be normalized device coordinates. Then the window coordinates (xw,yw) are computed as follows:
xw=(xnd+1)(
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yw=(ynd+1)(
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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.
GL_INVALID_OPERATION is generated if glViewport is executed between the execution of glBegin and the corresponding execution of glEnd.