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// Copyright (C) 2016 Jolla Ltd, author: <gunnar.sletta@jollamobile.com>
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#include <private/qglobal_p.h>
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
QT_BEGIN_NAMESPACE
struct QEvdevTouchFilter
{
QEvdevTouchFilter();
void initialize(float pos, float velocity);
void update(float pos, float velocity, float timeDelta);
float position() const { return x.x; }
float velocity() const { return x.y; }
private:
struct vec2 {
vec2(float x = 0.0f, float y = 0.0f) : x(x), y(y) { }
float x, y;
vec2 operator-(vec2 v) {
return vec2(x - v.x, y - v.y);
}
vec2 operator+(vec2 v) {
return vec2(x + v.x, y + v.y);
}
};
struct mat2 {
float a, b, c, d;
mat2(float a = 1.0f, float b = 0.0f, float c = 0.0f, float d = 1.0f)
: a(a)
, b(b)
, c(c)
, d(d)
{
}
mat2 transposed() const {
return mat2(a, c,
b, d);
}
mat2 inverted() const {
float det = 1.0f / (a * d - b * c);
return mat2( d * det, -b * det,
-c * det, a * det);
}
mat2 operator+(mat2 m) const {
return mat2(a + m.a, b + m.b,
c + m.c, d + m.d);
}
mat2 operator-(mat2 m) const {
return mat2(a - m.a, b - m.b,
c - m.c, d - m.d);
}
vec2 operator*(vec2 v) const {
return vec2(a * v.x + b * v.y,
c * v.x + d * v.y);
}
mat2 operator*(mat2 M) const {
return mat2(a * M.a + b * M.c,
a * M.b + b * M.d,
c * M.a + d * M.c,
c * M.b + d * M.d);
}
};
vec2 x;
mat2 A;
mat2 P;
mat2 Q;
mat2 R;
mat2 H;
};
inline QEvdevTouchFilter::QEvdevTouchFilter()
{
}
inline void QEvdevTouchFilter::initialize(float pos, float velocity)
{
x = vec2(pos, velocity);
P = mat2(0.0f, 0.0f,
0.0f, 0.0f);
Q = mat2(0.0f, 0.0f,
0.0f, 0.1f);
R = mat2(0.1f, 0.0f,
0.0f, 0.1f);
}
inline void QEvdevTouchFilter::update(float pos, float velocity, float dT)
{
A.b = dT;
// Prediction setp
x = A * x;
P = A * P * A.transposed() + Q;
// Correction step (complete with H)
// mat2 S = H * P * H.transposed() + R;
// mat2 K = P * H.transposed() * S.inverted();
// vec2 m(pos, velocity);
// vec2 y = m - H * x;
// x = x + K * y;
// P = (mat2() - K * H) * P;
// Correction step (without H as H is currently set to I, so we can ignore
// it in the calculations...)
mat2 S = P + R;
mat2 K = P * S.inverted();
vec2 m(pos, velocity);
vec2 y = m - x;
x = x + K * y;
P = (mat2() - K) * P;
}
QT_END_NAMESPACE
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