1
2/*
3 * Copyright 2010 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9
10
11#include "FlingState.h"
12#include "SkMatrix.h"
13#include "SkTime.h"
14
15#define DISCRETIZE_TRANSLATE_TO_AVOID_FLICKER   true
16
17static const float MAX_FLING_SPEED = 1500;
18
19static float pin_max_fling(float speed) {
20    if (speed > MAX_FLING_SPEED) {
21        speed = MAX_FLING_SPEED;
22    }
23    return speed;
24}
25
26static double getseconds() {
27    return SkTime::GetMSecs() * 0.001;
28}
29
30// returns +1 or -1, depending on the sign of x
31// returns +1 if x is zero
32static SkScalar SkScalarSign(SkScalar x) {
33    SkScalar sign = SK_Scalar1;
34    if (x < 0) {
35        sign = -sign;
36    }
37    return sign;
38}
39
40static void unit_axis_align(SkVector* unit) {
41    const SkScalar TOLERANCE = SkDoubleToScalar(0.15);
42    if (SkScalarAbs(unit->fX) < TOLERANCE) {
43        unit->fX = 0;
44        unit->fY = SkScalarSign(unit->fY);
45    } else if (SkScalarAbs(unit->fY) < TOLERANCE) {
46        unit->fX = SkScalarSign(unit->fX);
47        unit->fY = 0;
48    }
49}
50
51void FlingState::reset(float sx, float sy) {
52    fActive = true;
53    fDirection.set(sx, sy);
54    fSpeed0 = SkPoint::Normalize(&fDirection);
55    fSpeed0 = pin_max_fling(fSpeed0);
56    fTime0 = getseconds();
57
58    unit_axis_align(&fDirection);
59//    printf("---- speed %g dir %g %g\n", fSpeed0, fDirection.fX, fDirection.fY);
60}
61
62bool FlingState::evaluateMatrix(SkMatrix* matrix) {
63    if (!fActive) {
64        return false;
65    }
66
67    const float t =  getseconds() - fTime0;
68    const float MIN_SPEED = 2;
69    const float K0 = 5.0;
70    const float K1 = 0.02;
71    const float speed = fSpeed0 * (sk_float_exp(- K0 * t) - K1);
72    if (speed <= MIN_SPEED) {
73        fActive = false;
74        return false;
75    }
76    float dist = (fSpeed0 - speed) / K0;
77
78//    printf("---- time %g speed %g dist %g\n", t, speed, dist);
79    float tx = fDirection.fX * dist;
80    float ty = fDirection.fY * dist;
81    if (DISCRETIZE_TRANSLATE_TO_AVOID_FLICKER) {
82        tx = sk_float_round2int(tx);
83        ty = sk_float_round2int(ty);
84    }
85    matrix->setTranslate(tx, ty);
86//    printf("---- evaluate (%g %g)\n", tx, ty);
87
88    return true;
89}
90
91////////////////////////////////////////
92
93GrAnimateFloat::GrAnimateFloat() : fTime0(0) {}
94
95void GrAnimateFloat::start(float v0, float v1, float duration) {
96    fValue0 = v0;
97    fValue1 = v1;
98    fDuration = duration;
99    if (duration > 0) {
100        fTime0 = SkTime::GetMSecs();
101        if (!fTime0) {
102            fTime0 = 1;  // time0 is our sentinel
103        }
104    } else {
105        fTime0 = 0;
106    }
107}
108
109float GrAnimateFloat::evaluate() {
110    if (!fTime0) {
111        return fValue1;
112    }
113
114    double elapsed = (SkTime::GetMSecs() - fTime0) * 0.001;
115    if (elapsed >= fDuration) {
116        fTime0 = 0;
117        return fValue1;
118    }
119
120    double t = elapsed / fDuration;
121    if (true) {
122        t = (3 - 2 * t) * t * t;
123    }
124    return fValue0 + t * (fValue1 - fValue0);
125}
126