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
53 float scale;
54 if (SkScalarIsFinite(magSq)) {
55 scale = 1.0f / sk_float_sqrt(magSq);
56 } else {
57 // our magSq step overflowed to infinity, so use doubles instead.
58 // much slower, but needed when x, y or z is very large, otherwise we
59 // divide by inf. and return (0,0,0) vector.
60 double xx = fX;
61 double yy = fY;
62 double zz = fZ;
63 #ifdef SK_CPU_FLUSH_TO_ZERO
64 // The iOS ARM processor discards small denormalized numbers to go faster.
65 // Casting this to a float would cause the scale to go to zero. Keeping it
66 // as a double for the multiply keeps the scale non-zero.
67 double dscale = 1.0f / sqrt(xx * xx + yy * yy + zz * zz);
68 fX = x * dscale;
69 fY = y * dscale;
70 fZ = z * dscale;
71 return true;
72 #else
73 scale = (float)(1.0f / sqrt(xx * xx + yy * yy + zz * zz));
74 #endif
75 }
76 fX *= scale;
77 fY *= scale;
78 fZ *= scale;
79 return true;
80 }
81