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 "include/core/SkScalar.h"
12#include "include/core/SkTypes.h"
13
14#include <cmath>
15#include <utility>
16
17class SkScaleToSides {
18public:
19 // This code assumes that a and b fit in a float, and therefore the resulting smaller value
20 // of a and b will fit in a float. The side of the rectangle may be larger than a float.
21 // Scale must be less than or equal to the ratio limit / (*a + *b).
22 // This code assumes that NaN and Inf are never passed in.
23 static void AdjustRadii(double limit, double scale, SkScalar* a, SkScalar* b) {
24 SkASSERTF(scale < 1.0 && scale > 0.0, "scale: %g", scale);
25
26 *a = (float)((double)*a * scale);
27 *b = (float)((double)*b * scale);
28
29 if (*a + *b > limit) {
30 float* minRadius = a;
31 float* maxRadius = b;
32
33 // Force minRadius to be the smaller of the two.
34 if (*minRadius > *maxRadius) {
35 using std::swap;
36 swap(minRadius, maxRadius);
37 }
38
39 // newMinRadius must be float in order to give the actual value of the radius.
40 // The newMinRadius will always be smaller than limit. The largest that minRadius can be
41 // is 1/2 the ratio of minRadius : (minRadius + maxRadius), therefore in the resulting
42 // division, minRadius can be no larger than 1/2 limit + ULP.
43 float newMinRadius = *minRadius;
44
45 float newMaxRadius = (float)(limit - newMinRadius);
46
47 // Reduce newMaxRadius an ulp at a time until it fits. This usually never happens,
48 // but if it does it could be 1 or 2 times. In certain pathological cases it could be
49 // more. Max iterations seen so far is 17.
50 while (newMaxRadius + newMinRadius > limit) {
51 newMaxRadius = nextafterf(newMaxRadius, 0.0f);
52 }
53 *maxRadius = newMaxRadius;
54 }
55
56 SkASSERTF(*a >= 0.0f && *b >= 0.0f, "a: %g, b: %g, limit: %g, scale: %g", *a, *b, limit,
57 scale);
58
59 SkASSERTF(*a + *b <= limit,
60 "\nlimit: %.17f, sum: %.17f, a: %.10f, b: %.10f, scale: %.20f",
61 limit, *a + *b, *a, *b, scale);
62 }
63};
64#endif // ScaleToSides_DEFINED
65