Character Customization

1. Character Customization • Need millions of unique individuals • But, artists can only create dozens • How to solve? • Texture swapping • Tinting • Mesh splicing • Mesh morphing • Accessory polygons • Linear scaling • Bone scaling

2. Texture Swapping • This is much cheaper than creating a new model • Can segment model, swap each piece separately

3. Character Tinting • Slice character up into sections • Colorize each section with vertex colors • Results on next slide...

4. Character Tinting original texture tinted with GL_MODULATE tinted withphotoshop levelsdialog box

5. Tinting with “Levels” The Photoshop “levels” dialog: Each channel (R,G,B) has Scale, Offset, Power Gives broad range of results Trivially implemented in pixel shader Just offset without scale and power ok 90% of my shadersare implementations ofphotoshop effects

6. Tinting with Per-Pixel Alpha

7. Character Tinting original texture tinted withphotoshop levelsdialog box tinted withGL_DECAL and a per-pixel alpha

8. Mesh Splicing

9. Mesh Splicing Vertices have to line up perfectly – easy They have to have same vertex weights - hard This is a problem (and your artist isn’t going to solve it) Answer: don’t model it separately. Model it as one giant hydra-like object. Make sure seam vertices are shared.

10. Mesh Morphing I downloaded the normal head off the internet I made the witch and demon heads by moving vertices

11. Mesh Morphing download “makehuman” // assume three global vertex arrays: witchpos, normalpos, demonposvoid makehead(float witchfactor, float demonfactor){ for (int i=0; i<NUMVERTICES; i++) { output[i] = normalpos[i]; output[i] += witchfactor * (witchpos[i] – normalpos[i]); output[i] += demonfactor * (demonpos[i] – normalpos[i]); }}

12. Morphing vs Splicing • Important advantage of morphing: • With splicing, cannot reshape the boundaries • Cannot reshape waist (no fat characters) • Cannot reshape any other boundaries either. • No such limitations with morphing.

13. Morphing vs Splicing II • Does artist have to do “weird stuff”? • Splicing: • Make several meshes (easy) • Make edges line up (easy) • Maintain invariant that edge vertex weights are exactly equal. • Artist must use numeric vertex weights (very inconvenient) • Or, artist must use a “shared edge” (clumsy, counterintuitive) • Morphing: • Make a mesh (easy) • Insert extra vertices in interesting areas (easy) • Clone the mesh (easy) • Now tweak the clone without adding vertices (easy)

14. Accessory Polygons There are some things that morphing can’t do well. See image: For this, mesh splicing is better. Mesh splicing is easy when it’s not a choice of multiple meshes, only “mesh” or “no mesh.”

15. Morphing vs Splicing II • Does artist have to do “weird stuff”? • Splicing: • Make several meshes (easy) • Make edges line up (easy) • Maintain invariant that edge vertex weights are exactly equal. • Artist must use numeric vertex weights (very inconvenient) • Or, artist must use a “shared edge” (clumsy, counterintuitive) • Morphing: • Make a mesh (easy) • Insert extra vertices in interesting areas (easy) • Clone the mesh (easy) • Now tweak the clone without adding vertices (easy)

16. Using glScale • If scale is uniform: • Makes character look bigger, not taller. • If scale is nonuniform: • Doesn’t work. See image. • Need somethingsmarter – bonescaling.

17. Bone-based Scaling • Normally, you think about rotating bones. • But bones are represented as matrices – • meaning, you can translate and scale as well. • and, you can do nonuniform scaling. • sims modders have discovered that it’s possible to use nonuniform scaling to create fat sims: • That’s a lot of varietyfor just tweaking a fewscaling factors. Noextra memory usage!!!

18. City of Heroes