1 /*
2 * Copyright 2015 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #include "SkPoint3.h"
9
10 // Returns the square of the Euclidian distance to (x,y,z).
get_length_squared(float x,float y,float z)11 static inline float get_length_squared(float x, float y, float z) {
12 return x * x + y * y + z * z;
13 }
14
15 // Calculates the square of the Euclidian distance to (x,y,z) and stores it in
16 // *lengthSquared. Returns true if the distance is judged to be "nearly zero".
17 //
18 // This logic is encapsulated in a helper method to make it explicit that we
19 // always perform this check in the same manner, to avoid inconsistencies
20 // (see http://code.google.com/p/skia/issues/detail?id=560 ).
is_length_nearly_zero(float x,float y,float z,float * lengthSquared)21 static inline bool is_length_nearly_zero(float x, float y, float z, float *lengthSquared) {
22 *lengthSquared = get_length_squared(x, y, z);
23 return *lengthSquared <= (SK_ScalarNearlyZero * SK_ScalarNearlyZero);
24 }
25
Length(SkScalar x,SkScalar y,SkScalar z)26 SkScalar SkPoint3::Length(SkScalar x, SkScalar y, SkScalar z) {
27 float magSq = get_length_squared(x, y, z);
28 if (SkScalarIsFinite(magSq)) {
29 return sk_float_sqrt(magSq);
30 } else {
31 double xx = x;
32 double yy = y;
33 double zz = z;
34 return (float)sqrt(xx * xx + yy * yy + zz * zz);
35 }
36 }
37
38 /*
39 * We have to worry about 2 tricky conditions:
40 * 1. underflow of magSq (compared against nearlyzero^2)
41 * 2. overflow of magSq (compared w/ isfinite)
42 *
43 * If we underflow, we return false. If we overflow, we compute again using
44 * doubles, which is much slower (3x in a desktop test) but will not overflow.
45 */
normalize()46 bool SkPoint3::normalize() {
47 float magSq;
48 if (is_length_nearly_zero(fX, fY, fZ, &magSq)) {
49 this->set(0, 0, 0);
50 return false;
51 }
52 // sqrtf does not provide enough precision; since sqrt takes a double,
53 // there's no additional penalty to storing invScale in a double
54 double invScale;
55 if (sk_float_isfinite(magSq)) {
56 invScale = magSq;
57 } else {
58 // our magSq step overflowed to infinity, so use doubles instead.
59 // much slower, but needed when x, y or z is very large, otherwise we
60 // divide by inf. and return (0,0,0) vector.
61 double xx = fX;
62 double yy = fY;
63 double zz = fZ;
64 invScale = xx * xx + yy * yy + zz * zz;
65 }
66 // using a float instead of a double for scale loses too much precision
67 double scale = 1 / sqrt(invScale);
68 fX *= scale;
69 fY *= scale;
70 fZ *= scale;
71 if (!sk_float_isfinite(fX) || !sk_float_isfinite(fY) || !sk_float_isfinite(fZ)) {
72 this->set(0, 0, 0);
73 return false;
74 }
75 return true;
76 }
77