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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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