In OpenGL, how can one cut a triangle shaped hole from a square? making the hole transparent.
I m also using SDL, maybe it can be achieved with an SDL surface?
While doing it on a texture is truly the easier way out, if you need it to be a real shape, you might try using the GLUtesselator from GLU toolkit. See a tutorial for it here.
General usage is that you create a tesselator object, create two contours (the outer and the inner in a reverse direction) and the tesselator translates that into pure OpenGL commands. Of course if it s efficiency you re seeking you should implement or find some higher order system that operates on vertex buffers.
You can use a texture and alpha blending: the texture would contain a transparent triangle. See this tutorial on blending.
EDIT: Of course alpha blending doesn t change the geometry. For that you need to perform treatments that are more complicated. See this tutorial on realtime CSG.
Reference: Constructive Solid Geometry
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