unwanted stippling

OpenGL OpenGL: Basic Coding
1

Hi,

I am rendering polygons to a 2D view.

The polygons are like building blocks. If I do not show the polygon outline, I can see that I am getting some unwanted stippling effect underneath where the edges of two polygons meet.

Does anyone have any idea what it is that I’m seeing and how it might be remedied.

Thanks

matthew

2

Rasterization in 3D graphics is generally only stitch free when polygon edges share the exact same coordinates.
You will experience this with T-vertices, that is polygons where one long edge is aligned to two smaller ones like this

| poly 1 |
v0-------------------v1
v0----------v2-------v1
|
|
poly2 | poly 3
|

where poly 1 has an edge from v0 to v1 and polys 2 and 3 share the same vertices v0 and v1 but have the edge split at v2.
This is not going to end up without stitches!Different OpenGL implementations may show varying degrees of stitches, the more subpixel precision the rasterizer uses the better. But in general, avoid T-vertices!

[This message has been edited by Relic (edited 07-14-2003).]

3

Thanks for the reply relic.

I had considered that something like that could be causing the trouble.

For now it will have to remain for the time being. I actually render a border around each tesselated polygon which masks this effect anyhow.

It’s good to get the opinion of an expert. Thanks again.

matthew