1 /* 2 * Copyright 2016 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 #ifndef SkScaleToSides_DEFINED 9 #define SkScaleToSides_DEFINED 10 11 #include <cmath> 12 #include "SkScalar.h" 13 #include "SkTypes.h" 14 15 class SkScaleToSides { 16 public: 17 // This code assumes that a and b fit in a float, and therefore the resulting smaller value 18 // of a and b will fit in a float. The side of the rectangle may be larger than a float. 19 // Scale must be less than or equal to the ratio limit / (*a + *b). 20 // This code assumes that NaN and Inf are never passed in. 21 static void AdjustRadii(double limit, double scale, SkScalar* a, SkScalar* b) { 22 SkASSERTF(scale < 1.0 && scale > 0.0, "scale: %g", scale); 23 24 *a = (float)((double)*a * scale); 25 *b = (float)((double)*b * scale); 26 27 if (*a + *b > limit) { 28 float* minRadius = a; 29 float* maxRadius = b; 30 31 // Force minRadius to be the smaller of the two. 32 if (*minRadius > *maxRadius) { 33 SkTSwap(minRadius, maxRadius); 34 } 35 36 // newMinRadius must be float in order to give the actual value of the radius. 37 // The newMinRadius will always be smaller than limit. The largest that minRadius can be 38 // is 1/2 the ratio of minRadius : (minRadius + maxRadius), therefore in the resulting 39 // division, minRadius can be no larger than 1/2 limit + ULP. The newMinRadius can be 40 // 1/2 a ULP off at this point. 41 float newMinRadius = *minRadius; 42 43 // Because newMaxRadius is the result of a double to float conversion, it can be larger 44 // than limit, but only by one ULP. 45 float newMaxRadius = (float)(limit - newMinRadius); 46 47 // The total sum of newMinRadius and newMaxRadius can be upto 1.5 ULPs off. If the 48 // sum is greater than the limit then newMaxRadius may have to be reduced twice. 49 // Note: nextafterf is a c99 call and should be std::nextafter, but this is not 50 // implemented in the GCC ARM compiler. 51 if (newMaxRadius + newMinRadius > limit) { 52 newMaxRadius = nextafterf(newMaxRadius, 0.0f); 53 if (newMaxRadius + newMinRadius > limit) { 54 newMaxRadius = nextafterf(newMaxRadius, 0.0f); 55 } 56 } 57 *maxRadius = newMaxRadius; 58 } 59 60 SkASSERTF(*a >= 0.0f && *b >= 0.0f, "a: %g, b: %g, limit: %g, scale: %g", *a, *b, limit, 61 scale); 62 63 SkASSERTF(*a + *b <= limit, 64 "\nlimit: %.17f, sum: %.17f, a: %.10f, b: %.10f, scale: %.20f", 65 limit, *a + *b, *a, *b, scale); 66 } 67 }; 68 #endif // ScaleToSides_DEFINED 69
