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 /* * Copyright 2016 Google Inc. * * Use of this source code is governed by a BSD-style license that can be * found in the LICENSE file. */ #ifndef SkScaleToSides_DEFINED #define SkScaleToSides_DEFINED #include "SkScalar.h" #include "SkTypes.h" #include #include class SkScaleToSides { public: // This code assumes that a and b fit in a float, and therefore the resulting smaller value // of a and b will fit in a float. The side of the rectangle may be larger than a float. // Scale must be less than or equal to the ratio limit / (*a + *b). // This code assumes that NaN and Inf are never passed in. static void AdjustRadii(double limit, double scale, SkScalar* a, SkScalar* b) { SkASSERTF(scale < 1.0 && scale > 0.0, "scale: %g", scale); *a = (float)((double)*a * scale); *b = (float)((double)*b * scale); if (*a + *b > limit) { float* minRadius = a; float* maxRadius = b; // Force minRadius to be the smaller of the two. if (*minRadius > *maxRadius) { using std::swap; swap(minRadius, maxRadius); } // newMinRadius must be float in order to give the actual value of the radius. // The newMinRadius will always be smaller than limit. The largest that minRadius can be // is 1/2 the ratio of minRadius : (minRadius + maxRadius), therefore in the resulting // division, minRadius can be no larger than 1/2 limit + ULP. The newMinRadius can be // 1/2 a ULP off at this point. float newMinRadius = *minRadius; // Because newMaxRadius is the result of a double to float conversion, it can be larger // than limit, but only by one ULP. float newMaxRadius = (float)(limit - newMinRadius); // The total sum of newMinRadius and newMaxRadius can be upto 1.5 ULPs off. If the // sum is greater than the limit then newMaxRadius may have to be reduced twice. // Note: nextafterf is a c99 call and should be std::nextafter, but this is not // implemented in the GCC ARM compiler. if (newMaxRadius + newMinRadius > limit) { newMaxRadius = nextafterf(newMaxRadius, 0.0f); if (newMaxRadius + newMinRadius > limit) { newMaxRadius = nextafterf(newMaxRadius, 0.0f); } } *maxRadius = newMaxRadius; } SkASSERTF(*a >= 0.0f && *b >= 0.0f, "a: %g, b: %g, limit: %g, scale: %g", *a, *b, limit, scale); SkASSERTF(*a + *b <= limit, "\nlimit: %.17f, sum: %.17f, a: %.10f, b: %.10f, scale: %.20f", limit, *a + *b, *a, *b, scale); } }; #endif // ScaleToSides_DEFINED