I'm trying to figure out how the cracked and chipped glass effect in a Bioshock Infinite Burial at Sea Episode 2 works.

My current guess is that it is essentially a transparent shader with gloss. It would have a map defining the direction of reflections from the environment, with the cracks being significantly different from the mesh's normals. It would also include some kind of model of the angular dependence of the amount of refraction/transmission to reflection so that it can roughly approximate Fesnel's equations.

It doesn't appear to be a full refractive model, so I'm wondering how exactly this is implemented? Am I right with what I have said above?

enter image description here

  • \$\begingroup\$ Your description seems about right. The cracks are probably just a cracked glass texture applied on top. \$\endgroup\$ – glampert Apr 29 '14 at 2:41
  • \$\begingroup\$ @glampert by "texture applied on top" are you agreeing that texture is use as a normal map? Their appearance does change with position (probably should have put that in the question) \$\endgroup\$ – Lucas Apr 29 '14 at 2:50
  • \$\begingroup\$ I was thinking more something like this: carrigglass.net/images/glass.png And it might very well have a normal map too. \$\endgroup\$ – glampert Apr 29 '14 at 3:16
  • \$\begingroup\$ Hm I didn't play this game but I like the effect. I just tried to replicate it, you idea already works quite well. ;) \$\endgroup\$ – János Turánszki May 9 '14 at 16:24
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    \$\begingroup\$ Oh here you go: tinypic.com/r/2vanmur/8 (Sorry for the crap scene though) :) \$\endgroup\$ – János Turánszki May 9 '14 at 16:56

You could achieve a good approximation of this effect with regular environment mapping (to sample the reflective data) and a normal map (to simulate the surface discontinuities in the glass at the cracks), plus a simple decal-like texture modulated in (such as the one glampert linked in the comments:

enter image description here

If you have the artistic talent, you could probably hand-author this yourself. If not, you may be able to generate a reasonable facsimile using procedural generation techniques similar to those used to generate lighting bolts.

Note that the environment map likely need not be an accurate representation of the surrounding area, just enough to suggest similarity. This is basically how the windows in Assassin's Creed 4 were done (or at least, a part of how they were done).


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