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 /* * Copyright 2015 Google Inc. * * Use of this source code is governed by a BSD-style license that can be * found in the LICENSE file. */ #include "include/core/SkPoint3.h" #include "include/private/base/SkFloatingPoint.h" #include // Returns the square of the Euclidian distance to (x,y,z). static inline float get_length_squared(float x, float y, float z) { return x * x + y * y + z * z; } // Calculates the square of the Euclidian distance to (x,y,z) and stores it in // *lengthSquared. Returns true if the distance is judged to be "nearly zero". // // This logic is encapsulated in a helper method to make it explicit that we // always perform this check in the same manner, to avoid inconsistencies // (see http://code.google.com/p/skia/issues/detail?id=560 ). static inline bool is_length_nearly_zero(float x, float y, float z, float *lengthSquared) { *lengthSquared = get_length_squared(x, y, z); return *lengthSquared <= (SK_ScalarNearlyZero * SK_ScalarNearlyZero); } SkScalar SkPoint3::Length(SkScalar x, SkScalar y, SkScalar z) { float magSq = get_length_squared(x, y, z); if (SkScalarIsFinite(magSq)) { return sk_float_sqrt(magSq); } else { double xx = x; double yy = y; double zz = z; return (float)sqrt(xx * xx + yy * yy + zz * zz); } } /* * We have to worry about 2 tricky conditions: * 1. underflow of magSq (compared against nearlyzero^2) * 2. overflow of magSq (compared w/ isfinite) * * If we underflow, we return false. If we overflow, we compute again using * doubles, which is much slower (3x in a desktop test) but will not overflow. */ bool SkPoint3::normalize() { float magSq; if (is_length_nearly_zero(fX, fY, fZ, &magSq)) { this->set(0, 0, 0); return false; } // sqrtf does not provide enough precision; since sqrt takes a double, // there's no additional penalty to storing invScale in a double double invScale; if (sk_float_isfinite(magSq)) { invScale = magSq; } else { // our magSq step overflowed to infinity, so use doubles instead. // much slower, but needed when x, y or z is very large, otherwise we // divide by inf. and return (0,0,0) vector. double xx = fX; double yy = fY; double zz = fZ; invScale = xx * xx + yy * yy + zz * zz; } // using a float instead of a double for scale loses too much precision double scale = 1 / sqrt(invScale); fX *= scale; fY *= scale; fZ *= scale; if (!sk_float_isfinite(fX) || !sk_float_isfinite(fY) || !sk_float_isfinite(fZ)) { this->set(0, 0, 0); return false; } return true; }