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I want to stencil out some objects with openGL.

glClear(GL_STENCIL_BUFFER_BIT);
glColorMask(false, false, false, false);
glEnable(GL_STENCIL_TEST);
glStencilFunc(GL_EQUAL, 0, 1);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
glDisable(GL_DEPTH_TEST);
glColor4f(0,0,1,1.0f);

gl::draw(mVBO); //a sphere

glEnable(GL_DEPTH_TEST);
glColorMask(true, true, true, true);
glStencilFunc(GL_ALWAYS,0, 1);
glStencilOp(GL_REPLACE,GL_KEEP, GL_ZERO);

mTexture.enableAndBind();
gl::drawCube(Vec3f(0,3,0),Vec3f(13,13,13) );

glDisable(GL_STENCIL_TEST)

I tried so many hours to achieve a simple boolean operation, but I dont get it.

I want something like this:

img

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Isaac Jacob Troyer
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1 Answers1

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OpenGL's stencil buffer operates on the 2 dimensional pixel grid of the frame buffer. OpenGL itself has no notion of objects or a scene. It's merely drawing points, lines and triangles. So a real CSG is not possible with just OpenGL. However there are techniques that emulate CSG with stencil buffer operations, but they're quite complex. Google for "OpenGL CSG in the stencil buffer" to find some papers from the mid 1990-ies on the subject.

datenwolf
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