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* Copyright (C) 2012 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <input/Input.h>
#include <input/VelocityTracker.h>
#include <utils/Timers.h>
namespace android {
* Specifies parameters that govern pointer or wheel acceleration.
struct VelocityControlParameters {
// A scale factor that is multiplied with the raw velocity deltas
// prior to applying any other velocity control factors. The scale
// factor should be used to adapt the input device resolution
// (eg. counts per inch) to the output device resolution (eg. pixels per inch).
// Must be a positive value.
// Default is 1.0 (no scaling).
float scale;
// The scaled speed at which acceleration begins to be applied.
// This value establishes the upper bound of a low speed regime for
// small precise motions that are performed without any acceleration.
// Must be a non-negative value.
// Default is 0.0 (no low threshold).
float lowThreshold;
// The scaled speed at which maximum acceleration is applied.
// The difference between highThreshold and lowThreshold controls
// the range of speeds over which the acceleration factor is interpolated.
// The wider the range, the smoother the acceleration.
// Must be a non-negative value greater than or equal to lowThreshold.
// Default is 0.0 (no high threshold).
float highThreshold;
// The acceleration factor.
// When the speed is above the low speed threshold, the velocity will scaled
// by an interpolated value between 1.0 and this amount.
// Must be a positive greater than or equal to 1.0.
// Default is 1.0 (no acceleration).
float acceleration;
VelocityControlParameters() :
scale(1.0f), lowThreshold(0.0f), highThreshold(0.0f), acceleration(1.0f) {
VelocityControlParameters(float scale, float lowThreshold,
float highThreshold, float acceleration) :
scale(scale), lowThreshold(lowThreshold),
highThreshold(highThreshold), acceleration(acceleration) {
* Implements mouse pointer and wheel speed control and acceleration.
class VelocityControl {
/* Sets the various parameters. */
void setParameters(const VelocityControlParameters& parameters);
/* Resets the current movement counters to zero.
* This has the effect of nullifying any acceleration. */
void reset();
/* Translates a raw movement delta into an appropriately
* scaled / accelerated delta based on the current velocity. */
void move(nsecs_t eventTime, float* deltaX, float* deltaY);
// If no movements are received within this amount of time,
// we assume the movement has stopped and reset the movement counters.
static const nsecs_t STOP_TIME = 500 * 1000000; // 500 ms
VelocityControlParameters mParameters;
nsecs_t mLastMovementTime;
VelocityTracker::Position mRawPosition;
VelocityTracker mVelocityTracker;
} // namespace android