1/*
2 * Copyright 2017 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
17#ifndef AAUDIO_LINEAR_RAMP_H
18#define AAUDIO_LINEAR_RAMP_H
19
20#include <atomic>
21#include <stdint.h>
22
23/**
24 * Generate segments along a linear ramp.
25 * The ramp target can be updated from another thread.
26 * When the target is updated, a new ramp is started from the current position.
27 *
28 * The first ramp starts at 0.0.
29 *
30 */
31class LinearRamp {
32public:
33    LinearRamp() {
34        mTarget.store(1.0f);
35    }
36
37    void setLengthInFrames(int32_t frames) {
38        mLengthInFrames = frames;
39    }
40
41    int32_t getLengthInFrames() {
42        return mLengthInFrames;
43    }
44
45    /**
46     * This may be called by another thread.
47     * @param target
48     */
49    void setTarget(float target) {
50        mTarget.store(target);
51    }
52
53    float getTarget() {
54        return mTarget.load();
55    }
56
57    /**
58     * Force the nextSegment to start from this level.
59     *
60     * WARNING: this can cause a discontinuity if called while the ramp is being used.
61     * Only call this when setting the initial ramp.
62     *
63     * @param level
64     */
65    void forceCurrent(float level) {
66        mLevelFrom = level;
67        mLevelTo = level; // forces a ramp if it does not match target
68    }
69
70    float getCurrent() {
71        return mLevelFrom;
72    }
73
74    /**
75     * Get levels for next ramp segment.
76     *
77     * @param frames number of frames in the segment
78     * @param levelFrom pointer to starting amplitude
79     * @param levelTo pointer to ending amplitude
80     * @return true if ramp is still moving towards the target
81     */
82    bool nextSegment(int32_t frames, float *levelFrom, float *levelTo);
83
84private:
85
86    bool isRamping();
87
88    std::atomic<float>   mTarget;
89
90    int32_t mLengthInFrames  = 48000 / 50; // 20 msec at 48000 Hz
91    int32_t mRemaining       = 0;
92    float   mLevelFrom       = 0.0f;
93    float   mLevelTo         = 0.0f;
94};
95
96
97#endif //AAUDIO_LINEAR_RAMP_H
98