glViewport(3G)glViewport(3G)NAMEglViewport - set the viewport
GLsizei height );
Specify the lower left corner of the viewport rectangle, in pixels.
The initial value is (0,0). Specify the width and height of the view‐
port. When a GL context is first attached to a window, width and height
are set to the dimensions of that window.
DESCRIPTIONglViewport() specifies the affine transformation of x and y from nor‐
malized device coordinates to window coordinates. Let (x[n]d, y[n]d) 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_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().
ASSOCIATED GETSglGet() with argument GL_VIEWPORT
glGet() with argument GL_MAX_VIEWPORT_DIMS