Annotation of /examples/iso2d-demo/iso2d.diderot

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Revision 2044 - (view) (download)

1 :	jhr	1880	// 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 iso2d.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 :	jhr	2044	image(2)[] diderot = image("data/ddro-80.nrrd");
12 :	jhr	1880	field#1(2)[] F = ctmr ⊛ diderot;
13 :	jhr	1921	input int stepsMax = 12;
14 :	jhr	1880	real epsilon = 0.0001;
15 :
16 :			strand sample (int ui, int vi) {
17 :	jhr	1920	// world is 1x1 centered at (0.5, 0.5)
18 :	jhr	1880	output vec2 pos = [lerp(0.0, 1.0, -0.5, real(ui), real(gridSize)-0.5),
19 :			lerp(0.0, 1.0, -0.5, real(vi), real(gridSize)-0.5)];
20 :	jhr	1920	// set the isvalue to 50, 30, or 10, depending on whichever we're closest to
21 :	jhr	1880	real isoval = 50.0 if F(pos) >= 40.0
22 :			else 30.0 if F(pos) >= 20.0
23 :			else 10.0;
24 :			int steps = 0;
25 :			update {
26 :	jhr	1920	// We bail if we're no longer inside or taken too many steps.
27 :	jhr	1880	if (!inside(pos, F) || steps > stepsMax) {
28 :			die;
29 :			}
30 :			vec2 grad = ∇F(pos);
31 :			if (|grad| == 0.0) { // can't compute step if |∇F|, so have to bail
32 :			die;
33 :			}
34 :			vec2 norm = normalize(grad);
35 :			vec2 delta = -((F(pos) - isoval)/|grad|)*norm; // Newton-Raphson step
36 :			if (|delta| < epsilon) { // we've converged if step is small enough
37 :			stabilize;
38 :			}
39 :			pos += delta;
40 :			steps += 1;
41 :			}
42 :			}
43 :
44 :			initially { sample(ui, vi) | vi in 0..(gridSize-1), ui in 0..(gridSize-1) };

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