Re: Scroll direction algorithm

I think it's worth pointing out that unless you've planned ahead (or are
happy with some visual strangeness), this isn't going to work very well
for arbitrary meshes. Without constraints on the UV mapping, you're
going to get really crazy behavior along UV seams of the mesh. Even with
constraints, I don't see any general case where you're going to be able
to keep the mapped texture continuous across the mesh.

 

-Brian

 

From: Sim Dietrich [mailto:[email protected]] 
Sent: Monday, September 28, 2009 1:44 PM
To: Game Development Algorithms
Subject: Re: [Algorithms] Scroll direction algorithm

 

If you have a tangent space basis for the mesh then this gives you the
information you need.  You can use this to convert from left/right in
world, view or model space, and convert into UV space.

 

You can look up tangent space lighting tutorials, then interpret the
scroll direction as a light direction.  Put the scroll direction vector
in model space, then through the per-vertex or per-pixel tangent space
matrix ( which will account for the texture direction flips ), then
scale the resulting vector based on the scroll speed and time, then add
this to the initial model UVs.

 

That should work...

 

On Mon, Sep 28, 2009 at 9:22 AM, Zafar Qamar
<[email protected]> wrote:

Hi,

 

I have a question about an algorithm in a shader. I hope this is the
right place to post. 

 

I basically have a mesh that has a texture on. In my shader I want the
effect to generally look like it is moving across the mesh from left to
right. Imagine it is a simple scrolling texture with some spots on, for
the case of this question.

 

However, the mesh has been UV mapped such that generally the texture
looks like it is scrolling in the right direction, but some areas have
the texture scrolling in completely the wrong direction.

 

Is there some maths algorithm I can use to possibly get around this?

 

I apologise if my question is not clear.

 

Cheers

Zafar Qamar

 


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