Rotate edges between triangles where the area divided by the perimeter is smaller once the edge is rotated into the new state.This can be done for concave/convex polygons using a simple ear-clipping method (assuming we don't need to support holes). Is this of any help whatsoever? Should work for any polygon (convex/concave/with holes in them), I think, given that what exactly you do for intersecting squares/triangles handles such polygons. For these triangles you do the same as with the squares in the above pseudocode, except for the fact that you don't need to split the ones that cleanly inside your polygon as they are already triangles themselves. If you want as close to 60° as possible, you should start with tessellating the surface of your polygon with hexagons (with the size of the hexagon being your "amount of tessellation") and then checking each of the six 60°/60°/60° triangles that make up these hexagons. It will give you triangles with 45°/45°/90° angles though. Exact cases for the intersection squares are left as an exercise to the reader.Each resulting square is either cleanly outside your polygon (=ignore), cleanly inside your polygon (=split into two triangles of resulting tesselation along the diagonal) or intersects your polygon.Subdivide each square into four children (quad-tree like), where the number of iterations determines your "amount of tessellation".Place an axis-aligned enclosing square tightly around your polygon.Note: Most 2-D OpenGL games do not even need to address these issues, because each object in the game is simply a two-triangle rectangle, with a bitmap that has transparent sections.Doesn't actually sound that complicated, algorithmically. then render each piece with its own OpenGL call. cannot be rendered via that technique at all! To render it, we will have to break it into two or more pieces, like this. can be rendered via that technique, but only if you choose a good starting corner and direction, like so: Using this technique, it is easy to render any convex polygon: Simply start at any corner, and alternate corners in opposite directions around the polygon, like so:īut if you want to render a concave polygon, it’s not so easy. It just renders a triangle for each set of three consecutive points in the list of points you passed in.
Then it renders another triangle using points 1, 2, and 3. What OpenGL actually does is this: First it renders a triangle using points 0, 1, and 2. But to do that, the corners must be in a triangle-sequence order, like so: However, as a convenience, OpenGL allows you to pass in the four corners of the polygon and it will render the two triangles automatically. One way to do that is to first draw one triangle, then draw the other triangle. You cannot really draw a polygon with more than three corners, so if you want to draw a square (for example), you must draw it as two triangles: If you pass it a three-cornered polygon (i.e. Q: I’m trying to draw a simple polygon like this square:īut when I render it in OpenGL it comes out all broken looking, like this:Ī: Welcome to the world of triangle tessellation! It sounds complicated, but it’s really easy once you understand it. This complete article, unmodified, may be freely distributed for educational purposes. OpenGL Polygon Triangle Tessellation (Strip) and Corner Order Demystified OpenGL Polygon Triangle Tessellation (Strip) and Corner Order Demystified
0 kommentar(er)
