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Cross out everything outside the polygon.

I have a map, for simplicity let it be just one texture. At the top of this map, I have a polygon that indicates the route the user should follow.

What I want is to draw everything outside the black polygon. Or, of course, just draw things inside the polygon.

To explain this, I took a picture. Blue lines define a polygon, each of which is a point in the polygon. Red with yellow lines is the part that I want to delete from the picture, and I leave the red color only with purple lines. The polygon starts at A and ends at B.

enter image description here

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, , OpenGL. , . , , , . . , , , " ".

OpenGL , : . . , . , , , . / , .

:

  • , .

  • .

    glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
glEnable(GL_STENCIL_TEST);

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    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glStencilFunc(GL_ALWAYS, 0, 1);
glStencilOp(GL_KEEP, GL_KEEP, GL_INVERT);
glStencilMask(1);

  • , . (0.0, 0.0), , - . , . p1, p2,..., pN - , GL_TRIANGLE_FAN:

    (0.0f, 0.0f), p1, p2, ... , pN, p1

    , .

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    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glStencilFunc(GL_EQUAL, 1, 1);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

  • . , .

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