Graphics Reference
In-Depth Information
// Clear the color, depth, and stencil buffers. At this
// point, the stencil buffer will be 0x1 for all pixels.
glClear ( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT |
GL_STENCIL_BUFFER_BIT );
// Use the program object
glUseProgram ( userData−>programObject );
// Load the vertex position
glVertexAttribPointer ( userData−>positionLoc, 3, GL_FLOAT,
GL_FALSE, 0, vVertices );
glEnableVertexAttribArray ( userData−>positionLoc );
// Test 0:
//
// Initialize upper-left region. In this case, the stencil-
// buffer values will be replaced because the stencil test
// for the rendered pixels will fail the stencil test,
// which is
//
// ref mask stencil mask
// ( 0x7 & 0x3 ) < ( 0x1 & 0x7 )
//
// The value in the stencil buffer for these pixels will
// be 0x7.
//
glStencilFunc ( GL_LESS, 0x7, 0x3 );
glStencilOp ( GL_REPLACE, GL_DECR, GL_DECR );
glDrawElements ( GL_TRIANGLES, 6, GL_UNSIGNED_BYTE,
indices[0] );
// Test 1:
//
// Initialize the upper-right region. Here, we'll decrement
// the stencil-buffer values where the stencil test passes
// but the depth test fails. The stencil test is
//
// ref mask stencil mask
// ( 0x3 & 0x3 ) > ( 0x1 & 0x3 )
//
// but where the geometry fails the depth test. The
// stencil values for these pixels will be 0x0.
//
glStencilFunc ( GL_GREATER, 0x3, 0x3 );
glStencilOp ( GL_KEEP, GL_DECR, GL_KEEP );
glDrawElements ( GL_TRIANGLES, 6, GL_UNSIGNED_BYTE,
indices[1] );
(continues)
