- define the scissor box



C SPECIFICATION


PARAMETERS

       _param1, _param2 Specify  the  lower  left  corner  of the
                        scissor box.  Initially (0, 0).

       _param3, _param4 Specify the width and height of the scis-
                        sor  box.   When  a  GL  context is first
                        attached to a window, _param3 and _param4
                        are set to the dimensions of that window.


DESCRIPTION

       glScissor defines a rectangle, called the scissor box,  in
       window  coordinates.  The first two arguments, _param1 and
       _param2,  specify  the  lower  left  corner  of  the  box.
       _param3  and  _param4  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 ini-
       tially 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.


ERRORS

       GL_INVALID_VALUE is generated if either _param3 or _param4
       is negative.

       GL_INVALID_OPERATION is generated if glScissor is executed
       between  the  execution  of  glBegin and the corresponding
       execution of glEnd.















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