glScissor â define the scissor box
void glScissor( | GLint  | x, |
|  | GLint  | y, |
|  | GLsizei  | width, |
|  | GLsizei  | height); |
x, y+ Specify the lower left corner of the scissor box. + Initially (0, 0). +
width, height
+ 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 negative.
+
+ 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
+
+ Copyright © 1991-2006 + Silicon Graphics, Inc. This document is licensed under the SGI + Free Software B License. For details, see + http://oss.sgi.com/projects/FreeB/. +