Graphics Reference
In-Depth Information
(continued)
// Test 2:
//
// Initialize the lower-left region. Here we'll increment
// (with saturation) the stencil value where both the
// stencil and depth tests pass. The stencil test for
// these pixels will be
//
// ref mask stencil mask
// ( 0x1 & 0x3 ) == ( 0x1 & 0x3 )
//
// The stencil values for these pixels will be 0x2.
//
glStencilFunc ( GL_EQUAL, 0x1, 0x3 );
glStencilOp ( GL_KEEP, GL_INCR, GL_INCR );
glDrawElements ( GL_TRIANGLES, 6, GL_UNSIGNED_BYTE,
indices[2] );
// Test 3:
//
// Finally, initialize the lower-right region. We'll invert
// the stencil value where the stencil tests fails. The
// stencil test for these pixels will be
//
// ref mask stencil mask
// ( 0x2 & 0x1 ) == ( 0x1 & 0x1 )
//
// The stencil value here will be set to ~((2^s−1) & 0x1),
// (with the 0x1 being from the stencil clear value),
// where 's' is the number of bits in the stencil buffer.
//
glStencilFunc ( GL_EQUAL, 0x2, 0x1 );
glStencilOp ( GL_INVERT, GL_KEEP, GL_KEEP );
glDrawElements ( GL_TRIANGLES, 6, GL_UNSIGNED_BYTE,indices[3]);
// As we don't know at compile-time how many stencil bits are
// present, we'll query, and update, the correct value in the
// stencilValues arrays for the fourth tests. We'll use this
// value later in rendering.
glGetIntegerv ( GL_STENCIL_BITS, &numStencilBits );
stencilValues[3] = ~( ( (1 << numStencilBits) - 1 ) & 0x1 ) &
0xff;
// Use the stencil buffer for controlling where rendering
// will occur. We disable writing to the stencil buffer so we
// can test against them without modifying the values we
// generated.
glStencilMask ( 0x0 );
