Line data    Source code

       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           0 : static inline float get_length_squared(float x, float y, float z) {
      12           0 :     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           0 : static inline bool is_length_nearly_zero(float x, float y, float z, float *lengthSquared) {
      22           0 :     *lengthSquared = get_length_squared(x, y, z);
      23           0 :     return *lengthSquared <= (SK_ScalarNearlyZero * SK_ScalarNearlyZero);
      24             : }
      25             : 
      26           0 : SkScalar SkPoint3::Length(SkScalar x, SkScalar y, SkScalar z) {
      27           0 :     float magSq = get_length_squared(x, y, z);
      28           0 :     if (SkScalarIsFinite(magSq)) {
      29           0 :         return sk_float_sqrt(magSq);
      30             :     } else {
      31           0 :         double xx = x;
      32           0 :         double yy = y;
      33           0 :         double zz = z;
      34           0 :         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           0 : bool SkPoint3::normalize() {
      47             :     float magSq;
      48           0 :     if (is_length_nearly_zero(fX, fY, fZ, &magSq)) {
      49           0 :         this->set(0, 0, 0);
      50           0 :         return false;
      51             :     }
      52             : 
      53             :     float scale;
      54           0 :     if (SkScalarIsFinite(magSq)) {
      55           0 :         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           0 :         double xx = fX;
      61           0 :         double yy = fY;
      62           0 :         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           0 :         scale = (float)(1.0f / sqrt(xx * xx + yy * yy + zz * zz));
      74             : #endif
      75             :     }
      76           0 :     fX *= scale;
      77           0 :     fY *= scale;
      78           0 :     fZ *= scale;
      79           0 :     return true;
      80             : }