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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). | |
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 ). | |
21 static inline bool is_length_nearly_zero(float x, float y, float z, float *lengt
hSquared) { | |
22 *lengthSquared = get_length_squared(x, y, z); | |
23 return *lengthSquared <= (SK_ScalarNearlyZero * SK_ScalarNearlyZero); | |
24 } | |
25 | |
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 */ | |
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 faste
r. | |
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 } | |
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