GLint _y,
GLsizei _w_i_d_t_h,
GLsizei _h_e_i_g_h_t )
To enable and disable the scissor test, call ggllEEnnaabbllee and ggllDDiissaabbllee with argument GGLL__SSCCIISSSSOORR__TTEESSTT. 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) aalllloowwss mmooddiiffiiccaattiioonn ooff oonnllyy tthhee lloowweerr lleefftt ppiixxeell iinn tthhee wwiinnddooww,, aanndd ggllSScciissssoorr((00,,00,,00,,00)) 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.
GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if ggllSScciissssoorr is executed between the execution of ggllBBeeggiinn and the corresponding execution of ggllEEnndd.