nicolas's picture

C# Tessellation problem

Hey everybody, I'm trying to tessellate a geographic map in my 3D application. I must add that this is my first foray into openGL.
The first image shows the correct rendering of the map in an external program using the .Net System.Drawing library.
The second image shows the map rendered in my app using standard openGL. As you can see, many of the curves are not rendered correctly so tessellation is needed. I incorporated the openTK tessellation code into my code. I was able to render the star example but when I try to render my polygons, I get nothing, or errors.

Anybody else have experience with the openTK tessellator? Perhaps I can send you a list of coordinates of one of the polygons so you can try for yourself. This is my first foray into openGL so I am kinda lost here.


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objarni's picture

Sorry if stating the obvious, but just to make us communicate clearly:

1. What primitives? Tringles or polygons?
2. If polygons - OpenGL does NOT support concave polygons. Only convex ones. So you basically have to break apart any concave polygons in you data into convex ones.

nicolas's picture

So you basically have to break apart any concave polygons in you data into convex ones.

that's the whole aim of tessellation, no?

objarni's picture

Yeah, plus optimizing the result to avoid eg. line-like triangles. Just wanted to make sure we're using the same language.

nicolas's picture

OK I got it... or at least I made some progress... I think my coordinates were too close to each other, plus the camera wasn't at the right position which is why I didn't see anything.