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 <math.h>
20 #include <algorithm>
21 
22 namespace android {
23 namespace uirenderer {
24 
25 #define NON_ZERO_EPSILON (0.001f)
26 #define ALPHA_EPSILON (0.001f)
27 
28 class MathUtils {
29 public:
30     /**
31      * Check for floats that are close enough to zero.
32      */
isZero(float value)33     inline static bool isZero(float value) {
34         return (value >= -NON_ZERO_EPSILON) && (value <= NON_ZERO_EPSILON);
35     }
36 
isPositive(float value)37     inline static bool isPositive(float value) { return value >= NON_ZERO_EPSILON; }
38 
39     /**
40      * Clamps alpha value, and snaps when very near 0 or 1
41      */
clampAlpha(float alpha)42     inline static float clampAlpha(float alpha) {
43         if (alpha <= ALPHA_EPSILON) {
44             return 0;
45         } else if (alpha >= (1 - ALPHA_EPSILON)) {
46             return 1;
47         } else {
48             return alpha;
49         }
50     }
51 
52     /*
53      * Clamps positive tessellation scale values
54      */
clampTessellationScale(float scale)55     inline static float clampTessellationScale(float scale) {
56         const float MIN_SCALE = 0.0001;
57         const float MAX_SCALE = 1e10;
58         if (scale < MIN_SCALE) {
59             return MIN_SCALE;
60         } else if (scale > MAX_SCALE) {
61             return MAX_SCALE;
62         }
63         return scale;
64     }
65 
66     /**
67      * Returns the number of points (beyond two, the start and end) needed to form a polygonal
68      * approximation of an arc, with a given threshold value.
69      */
divisionsNeededToApproximateArc(float radius,float angleInRads,float threshold)70     inline static int divisionsNeededToApproximateArc(float radius, float angleInRads,
71                                                       float threshold) {
72         const float errConst = (-threshold / radius + 1);
73         const float targetCosVal = 2 * errConst * errConst - 1;
74 
75         // needed divisions are rounded up from approximation
76         return (int)(ceilf(angleInRads / acos(targetCosVal) / 2)) * 2;
77     }
78 
areEqual(float valueA,float valueB)79     inline static bool areEqual(float valueA, float valueB) { return isZero(valueA - valueB); }
80 
81     template <typename T>
clamp(T a,T minValue,T maxValue)82     static inline T clamp(T a, T minValue, T maxValue) {
83         return std::min(std::max(a, minValue), maxValue);
84     }
85 
lerp(float v1,float v2,float t)86     inline static float lerp(float v1, float v2, float t) { return v1 + ((v2 - v1) * t); }
87 };  // class MathUtils
88 
89 } /* namespace uirenderer */
90 } /* namespace android */
91 
92 #endif /* MATHUTILS_H */
93