The scissor test determines if 
lies within the scissor
rectangle defined by four values.
These values are set with
void Scissor ( int left, int bottom, sizei width, sizei height ) ;
If 
and 
,
then the scissor test passes.
Otherwise, the test fails and the fragment is discarded.
The test is enabled or disabled using Enable or Disable
using the constant SCISSOR_TEST.
When disabled,
it is as if the scissor test always passes.
If either width or height is less than zero,
then the error INVALID_VALUE is generated.
The state required consists of four integer values and a bit indicating
whether the test is enabled or disabled.
In the initial state left = bottom = 0;
width and height are determined by the size of the GL window.
Initially,
the scissor test is disabled.