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[diderot] Annotation of /trunk/test/iso2d.diderot
 [diderot] / trunk / test / iso2d.diderot

# Annotation of /trunk/test/iso2d.diderot

Revision 1134 - (view) (download)

 1 : jhr 1115 // iso2d 2 : // 3 : // Demo of finding isocontours via Newton-Raphson method. 4 : // Initializes positions on a grid, and each update applies one 5 : // step of Newton-Raphson. 6 : // 7 : // Process output with: 8 : // unu jhisto -i mip.txt -b 512 512 -min 0 0 -max 1 1 | unu 2op neq - 0 | unu quantize -b 8 -o iso2d.png 9 : 10 : int gridSize = 300; 11 : glk 1134 field#1(2)[] F = ctmr ⊛ load("../data/ddro-80.nrrd"); 12 : jhr 1115 int stepsMax = 10; 13 : real epsilon = 0.0001; 14 : 15 : strand sample (int ui, int vi) { 16 : output vec2 pos = [lerp(0.0, 1.0, -0.5, real(ui), real(gridSize)-0.5), 17 : lerp(0.0, 1.0, -0.5, real(vi), real(gridSize)-0.5)]; 18 : // set the isvalue to 50, 30, or 10, depending on whichever we're closest to 19 : glk 1134 real isoval = 50.0 if F(pos) >= 40.0 20 : else 30.0 if F(pos) >= 20.0 21 : else 10.0; 22 : jhr 1115 int steps = 0; 23 : update { 24 : // We bail if we're no longer inside or taken too many steps. 25 : if (!inside(pos, F) || steps > stepsMax) { 26 : jhr 1131 die; 27 : jhr 1115 } 28 : vec2 grad = ∇F(pos); 29 : real gmsq = grad • grad; 30 : // If |∇F|=0 we can't compute update; we have to bail 31 : if (gmsq == 0.0) { 32 : jhr 1131 die; 33 : jhr 1115 } 34 : // delta = Newton-Raphson step 35 : vec2 delta = -(F(pos) - isoval)*grad/gmsq; 36 : // We've converged if the update is small enough 37 : if (|delta| < epsilon) { 38 : stabilize; 39 : } 40 : pos = pos + delta; 41 : steps = steps + 1; 42 : } 43 : } 44 : 45 : initially { sample(ui, vi) | vi in 0..(gridSize-1), ui in 0..(gridSize-1) };

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