1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16#ifndef MATHUTILS_H
17#define MATHUTILS_H
18
19#include <algorithm>
20#include <math.h>
21
22namespace android {
23namespace uirenderer {
24
25#define NON_ZERO_EPSILON (0.001f)
26#define ALPHA_EPSILON (0.001f)
27
28class MathUtils {
29public:
30    /**
31     * Check for floats that are close enough to zero.
32     */
33    inline static bool isZero(float value) {
34        return (value >= -NON_ZERO_EPSILON) && (value <= NON_ZERO_EPSILON);
35    }
36
37    inline static bool isPositive(float value) {
38        return value >= NON_ZERO_EPSILON;
39    }
40
41    /**
42     * Clamps alpha value, and snaps when very near 0 or 1
43     */
44    inline static float clampAlpha(float alpha) {
45        if (alpha <= ALPHA_EPSILON) {
46            return 0;
47        } else if (alpha >= (1 - ALPHA_EPSILON)) {
48            return 1;
49        } else {
50            return alpha;
51        }
52    }
53
54    /*
55     * Clamps positive tessellation scale values
56     */
57    inline static float clampTessellationScale(float scale) {
58        const float MIN_SCALE = 0.0001;
59        const float MAX_SCALE = 1e10;
60        if (scale < MIN_SCALE) {
61            return MIN_SCALE;
62        } else if (scale > MAX_SCALE) {
63            return MAX_SCALE;
64        }
65        return scale;
66    }
67
68    /**
69     * Returns the number of points (beyond two, the start and end) needed to form a polygonal
70     * approximation of an arc, with a given threshold value.
71     */
72    inline static int divisionsNeededToApproximateArc(float radius,
73            float angleInRads, float threshold) {
74        const float errConst = (-threshold / radius + 1);
75        const float targetCosVal = 2 * errConst * errConst - 1;
76
77        // needed divisions are rounded up from approximation
78        return (int)(ceilf(angleInRads / acos(targetCosVal)/2)) * 2;
79    }
80
81    inline static bool areEqual(float valueA, float valueB) {
82        return isZero(valueA - valueB);
83    }
84
85    template<typename T>
86    static inline T clamp(T a, T minValue, T maxValue) {
87        return std::min(std::max(a, minValue), maxValue);
88    }
89
90    inline static float lerp(float v1, float v2, float t) {
91        return v1 + ((v2 - v1) * t);
92    }
93}; // class MathUtils
94
95} /* namespace uirenderer */
96} /* namespace android */
97
98#endif /* MATHUTILS_H */
99