glScissor - define the scissor box
GLsizei height );
Specify the lower left corner of the scissor box. Initially
(0, 0). Specify the width and height of the scissor
box. When a GL context is first attached to a window,
width and height are set to the dimensions of that window.
glScissor() defines a rectangle, called the scissor box,
in window coordinates. The first two arguments, x and y,
specify the lower left corner of the box. width and
height specify the width and height of the box.
To enable and disable the scissor test, call glEnable()
and glDisable() with argument GL_SCISSOR_TEST. The test is
initially disabled. While the test is enabled, only pixels
that lie within the scissor box can be modified by drawing
commands. Window coordinates have integer values at the
shared corners of frame buffer pixels. glScissor(0,0,1,1)
allows modification of only the lower left pixel in the
window, and glScissor(0,0,0,0) doesn't allow modification
of any pixels in the window.
When the scissor test is disabled, it is as though the
scissor box includes the entire window.
GL_INVALID_VALUE is generated if either width or height is
GL_INVALID_OPERATION is generated if glScissor() is executed
between the execution of glBegin() and the corresponding
execution of glEnd().
glGet() with argument GL_SCISSOR_BOX
glIsEnabled() with argument GL_SCISSOR_TEST
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