1/*
2 * Copyright (C) 2012 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 _ANDROIDFW_VELOCITY_CONTROL_H
18#define _ANDROIDFW_VELOCITY_CONTROL_H
19
20#include <androidfw/Input.h>
21#include <androidfw/VelocityTracker.h>
22#include <utils/Timers.h>
23
24namespace android {
25
26/*
27 * Specifies parameters that govern pointer or wheel acceleration.
28 */
29struct VelocityControlParameters {
30    // A scale factor that is multiplied with the raw velocity deltas
31    // prior to applying any other velocity control factors.  The scale
32    // factor should be used to adapt the input device resolution
33    // (eg. counts per inch) to the output device resolution (eg. pixels per inch).
34    //
35    // Must be a positive value.
36    // Default is 1.0 (no scaling).
37    float scale;
38
39    // The scaled speed at which acceleration begins to be applied.
40    // This value establishes the upper bound of a low speed regime for
41    // small precise motions that are performed without any acceleration.
42    //
43    // Must be a non-negative value.
44    // Default is 0.0 (no low threshold).
45    float lowThreshold;
46
47    // The scaled speed at which maximum acceleration is applied.
48    // The difference between highThreshold and lowThreshold controls
49    // the range of speeds over which the acceleration factor is interpolated.
50    // The wider the range, the smoother the acceleration.
51    //
52    // Must be a non-negative value greater than or equal to lowThreshold.
53    // Default is 0.0 (no high threshold).
54    float highThreshold;
55
56    // The acceleration factor.
57    // When the speed is above the low speed threshold, the velocity will scaled
58    // by an interpolated value between 1.0 and this amount.
59    //
60    // Must be a positive greater than or equal to 1.0.
61    // Default is 1.0 (no acceleration).
62    float acceleration;
63
64    VelocityControlParameters() :
65            scale(1.0f), lowThreshold(0.0f), highThreshold(0.0f), acceleration(1.0f) {
66    }
67
68    VelocityControlParameters(float scale, float lowThreshold,
69            float highThreshold, float acceleration) :
70            scale(scale), lowThreshold(lowThreshold),
71            highThreshold(highThreshold), acceleration(acceleration) {
72    }
73};
74
75/*
76 * Implements mouse pointer and wheel speed control and acceleration.
77 */
78class VelocityControl {
79public:
80    VelocityControl();
81
82    /* Sets the various parameters. */
83    void setParameters(const VelocityControlParameters& parameters);
84
85    /* Resets the current movement counters to zero.
86     * This has the effect of nullifying any acceleration. */
87    void reset();
88
89    /* Translates a raw movement delta into an appropriately
90     * scaled / accelerated delta based on the current velocity. */
91    void move(nsecs_t eventTime, float* deltaX, float* deltaY);
92
93private:
94    // If no movements are received within this amount of time,
95    // we assume the movement has stopped and reset the movement counters.
96    static const nsecs_t STOP_TIME = 500 * 1000000; // 500 ms
97
98    VelocityControlParameters mParameters;
99
100    nsecs_t mLastMovementTime;
101    VelocityTracker::Position mRawPosition;
102    VelocityTracker mVelocityTracker;
103};
104
105} // namespace android
106
107#endif // _ANDROIDFW_VELOCITY_CONTROL_H
108