Annotation of /branches/charisee/test/iso2d.diderot

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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 :	jhr	1640	// 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 :	jhr	1115
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 :	glk	1329	// GLKs recent changes (revision 1329) were made to make the code
29 :			// a more obvious implementation of Newton-Raphson, and also to create
30 :			// some obvious and not-so-obvious opportunties for optimization
31 :	jhr	1115	vec2 grad = ∇F(pos);
32 :	glk	1329	if (|grad| == 0.0) { // can't compute step if |∇F|, so have to bail
33 :	jhr	1131	die;
34 :	jhr	1115	}
35 :	glk	1329	vec2 norm = normalize(grad);
36 :			vec2 delta = -((F(pos) - isoval)/|grad|)*norm; // Newton-Raphson step
37 :			if (|delta| < epsilon) { // we've converged if step is small enough
38 :	jhr	1115	stabilize;
39 :			}
40 :	glk	1329	pos += delta;
41 :			steps += 1;
42 :	jhr	1115	}
43 :			}
44 :
45 :			initially { sample(ui, vi) | vi in 0..(gridSize-1), ui in 0..(gridSize-1) };

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