cg Vertex Shader and multiple objects

SKerner · 2005-06-16T03:17:01

I hope this is the right forum for my problem. If not, please redirect me. I'm trying add a wind animation to an OpenGL tree model. I figured out, the best way would be to use cg vertex shader. The problem is, the tree does not consist out of one mesh, but is constucted using cylinder shaped objects for each branch. I move recursively through my tree object, draw each tree and coordinate system with glRotate and glTranslate and draw the next part. This works really fine for static trees. But if I apply a simple Vertexshader to bend the branches, the next branch is not longer connected to the previous one, cause the shader does not transform glRotate and glTranslate. This tears my branches apart. How can I animate serveral connected objects via vertex shading without losing the connection? Do I need to transform my tree in one mesh, or is there a way to do this in different coordinate systems?

Graphics and GPU Programming Programming OpenGL

Started by SKerner June 10, 2005 04:29 AM

11 comments, last by SKerner 18 years, 10 months ago

Anonymous

June 15, 2005 09:08 AM

Quote:Original post by skow
Quote:Original post by SKerner
That do you mean by 'animating the model'?
Do you mean windmovement without shader and to move the branches by altering the angle instead?

I mean by using a modeling program to make the tree and keyframe animate it.

I see. This is out of question, cause I wrote a growth simulation to automatically generate the trees. I can't model them.

skow

248

June 15, 2005 11:30 AM

Quote:Original post by Anonymous Poster
I see. This is out of question, cause I wrote a growth simulation to automatically generate the trees. I can't model them.

Something you could try is only changing the x/z values dependent on the y value. This would cause the tree to sway back and forth, while keeping everything connected. Make sure to have the effect be small at the root of the tree, you don’t want the tree moving around ;)

www.skowOnline.com

SKerner

122

Author

June 16, 2005 03:17 AM

I already tried this. I defined a wind vector and gave every vertex a flexibility value, depending on the thickness of the branch.
But the movement is still quite unrealistic, cause it makes the whole tree sway back and fourth like a spring.
I wonder how Speedtree is dowing the movement stuff. Are there any papers out there concerning Speedtree?

cg Vertex Shader and multiple objects

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