Quote:Any suggestions on easy ways to clip the decals? Or to bend them around corners where they lay on multiple faces?

The best reference I know of on this is Eric Lengyel's article 'Applying Decals to Arbitrary Surfaces' in GPG2. The book also comes with code for the implementation on a CD. My decal system is based on this method, and it works great.

The basic idea is as follows. You construct the decal from an intersection point (i.e. where a bullet hits) and the surface normal at that point. From this info you create a rectangular volume centered on the intersection point and aligned with the normal. The width and height of the volume are the desired width and height of the decal, and the depth is chosen as appropriate to include the appropriate polygons.

Then what you do is take each surface that intersects this volume, and add its triangles to the decal one by one. As the triangles are added, they are clipped to the volume so that only the portions inside the volume remain.

What you are left with is a decal surface that perfectly follows the contour of the surfaces it affects. You can then use the z-tweaking method of your choice to avoid z-fighting.

The implementation is a little involved, but it's not too bad. If you don't have GPG2, I highly recommend picking it up for the source code if nothing else.

Quote:Original post by jyk
... Smart stuff...

So is this a multi-texturing effect rather than a texture mapped quad?

Quote:So is this a multi-texturing effect rather than a texture mapped quad?

If you're refering to the Lengyel method, no, it doesn't use multitexturing. Multitexturing would require that the exact input tris be used, but in this case the tris must be clipped to get the right results.

Also, it's only a quad in the simplest case, i.e. a flat surface with no clipping. In the general case, it's a mesh of tris that maps to the underlying surface.

Not sure if I answered your question, though...

Maybe a good idea to check for the 3 closest point on the 3 triangle-edges, if a point lies in the bullet-hole area then check which triangle shares the same edge, where the point was on, and put another decal on that point facing it to the normal of that triangle. should work too