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 _LIBINPUT_VELOCITY_CONTROL_H
18 #define _LIBINPUT_VELOCITY_CONTROL_H
19 
20 #include <input/Input.h>
21 #include <input/VelocityTracker.h>
22 #include <utils/Timers.h>
23 
24 namespace android {
25 
26 /*
27  * Specifies parameters that govern pointer or wheel acceleration.
28  */
29 struct 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 
VelocityControlParametersVelocityControlParameters64     VelocityControlParameters() :
65             scale(1.0f), lowThreshold(0.0f), highThreshold(0.0f), acceleration(1.0f) {
66     }
67 
VelocityControlParametersVelocityControlParameters68     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  */
78 class VelocityControl {
79 public:
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 
93 private:
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 // _LIBINPUT_VELOCITY_CONTROL_H
108