RE: [Algorithms] Bullets on walls

[<ma...@ci...>]

We do it this way:

If the decal does not cross a polygon boundary with a high enough crease 
angle, draw it as a quad.  Use ZBIAS if supported and/or move it along the 
normal to lift it off the surface.

Otherwise draw it as decal, as per Jaimi's method.  Remember to enable 
ALPHATEST so there's no overdraw or fill-rate hit even if the base triangle 
is large and has several decals.

Mipmapping is still a problem - clamp mip levels to a minimum size (16x16 or 
32x32) and make sure your algorithm maintains the alpha==0 border all the 
way, otherwise decals at oblique angles will bleed over the whole base 
triangle.  For small decals like bulletholes just don't mipmap them (and use 
a suitably low-res texture).


-=Mark=-

Mark Atkinson, Technical Director, Computer Artworks Ltd.
http://www.artworks.co.uk

> Using overlay textures would require you to use a ton of unique textures. 
> .
> . can become very unreasonable quickly.
> 
> Gary
> 
> -----Original Message-----
> From: Mark Wayland [mailto:mwa...@to...]
> Sent: Thursday, July 20, 2000 9:55 PM
> To: gda...@li...
> Subject: Re: [Algorithms] Bullets on walls
> 
> 
> An extension to Jaimi's method may be to render the bullet holes to an
> overlay texture (of which you would have a maximum number) which is only
> rendered *once* on-top of the wall. With complex texture mapping this is
> obviously not possible, but perhaps for simple quads it would be 
> acceptable
> ?
> 
> Perhaps some form of scalable solution - like use Jaimi's method for a 
> small
> number and when a threshold is reached, combine them into the single 
> texture
> as I've mentioned and repeat ... ??
> 
> Just my 2c worth ...
> 
> Mark
> 
> > In d3d, this is the way I do it:
> >
> > Create decals with a one pixel transparent border.
> > Then, set the texture address mode to "Clamp".
> > Calculate new UV coordinates for your decal based on the wall, instead
> > of the Decal - then redraw the entire wall with your decal texture and
> > new UV coordinates.
> > This way you do not have to clip at all. I would assume you could
> > do the same in OpenGL.
> >
> > Jaimi
> 
> 
> 
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