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## Theory behind painting decals directly to UV texture

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### #1MikeNatty  Members

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Posted 20 February 2012 - 03:50 PM

Hi all, first post at gemedev. Fantastic resource, hoping someone can offer a little advice.

First off, I haven't done a heap of game development - mostly application dev - and as such, need a little guidance.

My problem is this:
• I have a complex uv textured mesh. Any 'section' of this mesh could contain, concave, convex and/or cylindrical forms)
• I need to be able to place a decal of sorts onto this mesh and be able to adjust translation, scale and orientation of the decal
• The solution must be able to wrap around the surface completely as a sticker would (so I can't use projection onto the surface as this would not allow wrapping around cylindrical portions)
• Performance is not critical, a simple solution would be preferred over performance-optimized one
I have looked into Eric Lengyel's Applying Decals to Arbitray Surfaces from Game Programming Gems II, and although a little over my head at this stage, I will be able to work through it if it is indeed the best solution. (I want to ask here first before devoting too much time to this solution).

So... If I can't use projection, what is the process for mapping the decal to the texture?

To begin, I would:
• Find the intersection point for the decal/stencil
• Find the face normal and an angle of orientation
• Now... How can I continue to follow this orientation line along the different faces? (i.e. the vector changes each time we enter a new face)
If I could work that out, then I could apply the decal directly to the texture...perhaps!

Would * really* appreciate any guidance you can offer and links to any resources that may be of some help.

My math knowledge is pretty basic but I can usually learn what I need to get the job done.

Big thanks,
Mike

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