Comments on: Triangle Strip for Grids – A Construction

By: Ricardo Sanchez

Ricardo Sanchez — Wed, 10 Aug 2011 20:33:05 +0000

Dan excellent tutorial!

I am new to opengl in general and I am struggling to implement this, I start a stackoverflow topic on the subject and I wonder if you will be able to have a look and let me know and assist on my implementation, any help will be much appreciated

Here is the link
http://stackoverflow.com/questions/7011017/help-getting-vertex-indices-from-a-grid

Thanks

By: dan.lecocq

dan.lecocq — Thu, 10 Mar 2011 13:39:58 +0000

As far as I know, WebGL doesn’t have display lists. At least in Chrome and WebKit/Safari, I didn’t find a gl.NewList(). I’d be surprised if there were, as it’s supposed to essentially follow the OpenGL ES 2.0 spec, which doesn’t include display lists.

In what environment did you find gl.NewList()? You’ve make me curious!

By: John

John — Wed, 09 Mar 2011 23:16:20 +0000

Correction: it looks like gl.NewList (); is available. Was it added after this article? Feel free to skip my post or update the article if display lists are truly currently supported in webgl.

Thanks

By: John

John — Wed, 09 Mar 2011 23:11:37 +0000

Thanks for trying to cheer me up. I still prefer display lists in more ways than one. It’s a shame they’re trying to bury such a flexible and powerful feature. VBOs are just a crippled version of the display list.

By: Noa

Noa — Mon, 07 Mar 2011 14:55:09 +0000

Dan,

Yes I was using the FFP, pre-computing the normals per vertex on cpu. Because the orientation of the triangles on the triangle strip alternates, my normals where miss-oriented on every odd row. Because I need to compute normals per vertex, I had to modify the algorithm and add some glue.

By: dan.lecocq

dan.lecocq — Tue, 01 Mar 2011 15:13:15 +0000

I hadn’t noticed any funny business with the normals, but that’s good to know! I wonder if it was because I was using my own shader — were you using the fixed-function pipeline?

By: Noa

Noa — Mon, 28 Feb 2011 20:51:54 +0000

It was very helpful for me to, thanks. I implemented it, and realized at some point that the normals are inverted at every change of row (because I’m setting normals per vertex). I had to add some more “glue” every time. So in the previous explanation, I inserted “7″ twice, and got 0, 4, 1, 5, 2, 6, 3, 7,7,7,8, 12, 9, 13, 10, 14, 11, and 15. That way the normal stays in the right orientation.

Noa

By: dan.lecocq

dan.lecocq — Wed, 31 Mar 2010 12:08:58 +0000

Here columns refers to the columns of vertices, like (0, 4, 8, 12) or (2, 6, 10, 14). Suppose we have n vertices in a row (in this case, 4) and we are at vertex indexed a (let's say 5). Then a + 4 would be the vertex below it, and a - 4 would be the vertex above it. If instead of adding or subtracting n = 4 from a, we added or subtracted n + 1 = 5, we would get the vertex in the row below it, and one column to the right. For example, vertex a + 5 = 10 is diagonal from a in this fashion. Using n - 1 = 3 does the same thing, except for one column to the left (a + 3 = 8 is one row down from a and one column to the left). I hope this clarifies a little bit!

By: jeckil

jeckil — Wed, 31 Mar 2010 03:32:08 +0000

One of the best tutorials I have ever seen on the theory behind the topic.

One thing I don’t understand yet:

“the 3 and 5 are explained by the fact that we need to change columns in the mesh, by one step at a time.” Can you elaborate on this more please? what do the columns mean?, one step at a time?

Thanks a lot. :)