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fix computeFaceNormal: use corner whose angle is closest to right angle for cross product #131

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fix computeFaceNormal: use corner whose angle is closest to right angle for cross product #131

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621e236
fix computeFaceNormal: use corner whose angle is closest to right ang…
henkson Dec 21, 2023
9b986ca
fix build on windows systems; use M_PI_2 constant instead of M_PI * 0.5f
henkson Jan 16, 2024
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31 changes: 28 additions & 3 deletions source/xatlas/xatlas.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,7 @@ Copyright (c) 2012 Brandon Pelfrey
#include <assert.h>
#include <float.h> // FLT_MAX
#include <limits.h>
#define _USE_MATH_DEFINES
#include <math.h>
#define __STDC_LIMIT_MACROS
#include <stdint.h>
Expand Down Expand Up @@ -814,6 +815,12 @@ static float length(const Vector3 &v)
return sqrtf(lengthSquared(v));
}

static float angle(const Vector3 &a, const Vector3 &b)
{
const Vector3 c = cross(a, b);
return abs(atan2(length(c), dot(a, b)));
}

static bool isNormalized(const Vector3 &v, float epsilon = kNormalEpsilon)
{
return equal(length(v), 1.0f, epsilon);
Expand Down Expand Up @@ -2707,9 +2714,27 @@ class Mesh
const Vector3 &p0 = m_positions[m_indices[face * 3 + 0]];
const Vector3 &p1 = m_positions[m_indices[face * 3 + 1]];
const Vector3 &p2 = m_positions[m_indices[face * 3 + 2]];
const Vector3 e0 = p2 - p0;
const Vector3 e1 = p1 - p0;
const Vector3 normalAreaScaled = cross(e0, e1);
const Vector3 e00 = p2 - p0;
const Vector3 e01 = p1 - p0;
const Vector3 e10 = p0 - p1;
const Vector3 e11 = p2 - p1;
const Vector3 e20 = p1 - p2;
const Vector3 e21 = p0 - p2;

// use the corner whose angle is the closest to a right angle,
// as that will give the most stable results for the cross product calculation
const float diff0 = abs(M_PI_2 - angle(e00, e01));
const float diff1 = abs(M_PI_2 - angle(e10, e11));
const float diff2 = abs(M_PI_2 - angle(e20, e21));
Vector3 normalAreaScaled;
if (diff0 <= diff1 && diff0 <= diff2) {
normalAreaScaled = cross(e00, e01);
} else if (diff1 <= diff0 && diff1 <= diff2) {
normalAreaScaled = cross(e10, e11);
} else {
normalAreaScaled = cross(e20, e21);
}

return normalizeSafe(normalAreaScaled, Vector3(0, 0, 1));
}

Expand Down