void CMaSimView:Subtract()
{
glEnable(GL_DEPTH_TEST);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glCullFace(GL_FRONT); /* controls which face of a to use */
RenderCutter(); /* draw a face of a into depth buffer */
/* use stencil plane to find parts of a in b */
glDepthMask(GL_FALSE);
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_ALWAYS, 0, 0);
glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);
glCullFace(GL_BACK);
RenderObject(); /* increment the stencil where the front face of b is
drawn */
glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);
glCullFace(GL_FRONT);
RenderObject(); /* decrement the stencil buffer where the back face of b is drawn */
glDepthMask(GL_TRUE);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glStencilFunc(GL_NOTEQUAL, 0, 1);
glDisable(GL_DEPTH_TEST);
glCullFace(GL_FRONT);
RenderCutter();
////////////////////
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glEnable(GL_DEPTH_TEST);
glDisable(GL_STENCIL_TEST);
glDepthFunc(GL_ALWAYS);
RenderObject(); /* draw the front face of a, fixing the depth buffer */
glDepthFunc(GL_LESS);
/////////////////
glEnable(GL_DEPTH_TEST);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glCullFace(GL_BACK); /* controls which face of a to use */
RenderObject(); /* draw a face of a into depth buffer */
/* use stencil plane to find parts of a in b */
glDepthMask(GL_FALSE);
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_ALWAYS, 0, 0);
glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);
glCullFace(GL_BACK);
RenderCutter(); /* increment the stencil where the front face of b is
drawn */
glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);
glCullFace(GL_FRONT);
RenderCutter(); /* decrement the stencil buffer where the back face
of b is drawn */
glDepthMask(GL_TRUE);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glStencilFunc(GL_EQUAL, 0, 1);
glDisable(GL_DEPTH_TEST);
glCullFace(GL_BACK);
RenderObject();
glDisable(GL_STENCIL_TEST);
}