CS3451-P5

1
CS3451-P5

• Rolling a disk on a triangle mesh

2
Show path

• Define a data structure for the path
  (pointsnormals)
• pt gP new pt5000 // path points
• vec gN new vec5000 // path normaLS
• vec gD new vec (1,0,0) // current direction
• int gn 0 // number of path
  points
• int gm 0 // number of last
  undisplayed steps
• Visualize it (a bit offset from the surface)
• Let the user add points
• By clicking
• void keys()
• if (key'r') C.setMark() M.hitTriangle()
  M.gstart()
• if (key't') C.setMark() M.hitTriangle()
  M.gextend()

3
Start the path

• User click selects corner c and sets mark (green)
• if (key'r') C.setMark() M.hitTriangle()
  M.gstart()
• void gstart() gP0g(c)
• Compute exit point S1 on opposite edge
• Compute edge-normal at S1
• Compute new (reflected) D
• Show them all

4
Extend the path

• if (key't') M.gextend() if (jumps)
  M.gjump(C)
• void gextend()vec N cross(triNormal(t(c)),gD)
  
• if (dot(N,V(gPgn-1,g(c)))gt0) cn(c) else
  cp(c) gmove()
• void gmove()
• Similar to gstart

5
Smooth normals

• if (key's') M.gsmoothNormals()
• void gsmoothNormals () vec L new vecgn
• // one line

6
Display a subset of the path

• int gn 0 // number of path
  points
• int gm 0 // number of last not
  displayed steps
• void keys()
• if (key',') M.gm
• if (key'.') M.gm--
• Useful to compute the path first, then smooth the
  normals, then roll

7
Follow the disk with the camera

• if (keyJ') jumps!jumps
• if (key't') M.gextend() if (jumps)
  M.gjump(C)
• void gjump (cam C)
• C.FP(gPgn-gm-1)
• C.E S(S(C.F,-200,gD),200,gNgn-gm-1)
• C.US(-1,gNgn-gm-1)
• C.sD200
• C.pullE()
• C.pose()

8
Display disk

• void gshow() stroke(red) gshowPath()
  stroke(blue) gshowNormals() stroke(magenta)
  fill(blue) gshowPoints() fill(orange)
  gdisk(30)
• void gdisk(float d) float L0 // measure length
  of displayed path (to gm)
• show polygonized disk above gPgn-gm-1
• using gNgn-gm-1 and D as basis
  vectors.
• rotate it to reflect distance traveled L
• I show it missing one slice to check the roll
  (you should put a texture)

9
Results

• 3 hours
• 40 lines of code (total)