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sipickles

Dropped pixels while geomorphing

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sipickles    240
Hi, A brief period of elation followed my recent success at implementing geomorphing with geoclipmapping, a la Hugues Hoppe. However, it was short-lived. The geomorphing can be seen clearly working in wireframe mode, smoothing the transitions between different levels of detail. However, in solid mode there are occasional dropped pixels between the LODs: I imagine this maybe resulting from slightly different positions being calculated for the vertex's morphed position than the real unmorphed position, maybe simply down to floating point inaccuracies. Consulting the Hoppe paper, this problem is mentioned briefly: "Although the geometry transitions eliminate gaps, the T-junctions along the boundaries still result in dropped pixels during rasterization. To stitch adjacent levels of detail into a watertight mesh, we use the simple solution of rendering zero area triangles along the render region boundaries." Can anyone demystify this for me a little? I have a feeling my implementation has a flaw in that each LOD has its own VB and IB, so it would not be possible to stitch across different LODs. What are the zero area triangles referred to? Any advice gratefully received. Thanks Simon

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Supernat02    604
Are you taking the T junction LOD transitions into account? There are several ways to deal with these. Rendering degenerate (zero area) triangles is one way to solve the issue. Simply render a triangle (one of the vertices shares a point with one of the corners of your patch, the second shares a point in the middle of the edge of the patch, and the third vertex shares the other corner of the patch (making a line down one side of the patch for example). This triangle gets zero area but closes the T junction. It's been a while since I've messed with this, but I think that's what he's talking about...

Good luck,
Chris

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