src/views/SkTouchGesture.cpp

/*
    Copyright 2010 Google Inc.

    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

         http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
 */


#include "SkTouchGesture.h"
#include "SkMatrix.h"
#include "SkTime.h"

#define DISCRETIZE_TRANSLATE_TO_AVOID_FLICKER   true

static const float MAX_FLING_SPEED = 1500;

static float pin_max_fling(float speed) {
    if (speed > MAX_FLING_SPEED) {
        speed = MAX_FLING_SPEED;
    }
    return speed;
}

static double getseconds() {
    return SkTime::GetMSecs() * 0.001;
}

// returns +1 or -1, depending on the sign of x
// returns +1 if x is zero
static SkScalar SkScalarSign(SkScalar x) {
    SkScalar sign = SK_Scalar1;
    if (x < 0) {
        sign = -sign;
    }
    return sign;
}

static void unit_axis_align(SkVector* unit) {
    const SkScalar TOLERANCE = SkDoubleToScalar(0.15);
    if (SkScalarAbs(unit->fX) < TOLERANCE) {
        unit->fX = 0;
        unit->fY = SkScalarSign(unit->fY);
    } else if (SkScalarAbs(unit->fY) < TOLERANCE) {
        unit->fX = SkScalarSign(unit->fX);
        unit->fY = 0;
    }
}

void SkFlingState::reset(float sx, float sy) {
    fActive = true;
    fDirection.set(sx, sy);
    fSpeed0 = SkPoint::Normalize(&fDirection);
    fSpeed0 = pin_max_fling(fSpeed0);
    fTime0 = getseconds();

    unit_axis_align(&fDirection);
//    printf("---- speed %g dir %g %g\n", fSpeed0, fDirection.fX, fDirection.fY);
}

bool SkFlingState::evaluateMatrix(SkMatrix* matrix) {
    if (!fActive) {
        return false;
    }

    const float t =  (float)(getseconds() - fTime0);
    const float MIN_SPEED = 2;
    const float K0 = 5;
    const float K1 = 0.02f;
    const float speed = fSpeed0 * (sk_float_exp(- K0 * t) - K1);
    if (speed <= MIN_SPEED) {
        fActive = false;
        return false;
    }
    float dist = (fSpeed0 - speed) / K0;

//    printf("---- time %g speed %g dist %g\n", t, speed, dist);
    float tx = fDirection.fX * dist;
    float ty = fDirection.fY * dist;
    if (DISCRETIZE_TRANSLATE_TO_AVOID_FLICKER) {
        tx = (float)sk_float_round2int(tx);
        ty = (float)sk_float_round2int(ty);
    }
    matrix->setTranslate(tx, ty);
//    printf("---- evaluate (%g %g)\n", tx, ty);

    return true;
}

///////////////////////////////////////////////////////////////////////////////

static const SkMSec MAX_DBL_TAP_INTERVAL = 300;
static const float MAX_DBL_TAP_DISTANCE = 100;
static const float MAX_JITTER_RADIUS = 2;

// if true, then ignore the touch-move, 'cause its probably just jitter
static bool close_enough_for_jitter(float x0, float y0, float x1, float y1) {
    return  sk_float_abs(x0 - x1) <= MAX_JITTER_RADIUS &&
            sk_float_abs(y0 - y1) <= MAX_JITTER_RADIUS;
}

///////////////////////////////////////////////////////////////////////////////

SkTouchGesture::SkTouchGesture() {
    this->reset();
}

SkTouchGesture::~SkTouchGesture() {
}

void SkTouchGesture::reset() {
    fTouches.reset();
    fState = kEmpty_State;
    fLocalM.reset();
    fGlobalM.reset();

    fLastUpT = SkTime::GetMSecs() - 2*MAX_DBL_TAP_INTERVAL;
    fLastUpP.set(0, 0);
}

void SkTouchGesture::flushLocalM() {
    fGlobalM.postConcat(fLocalM);
    fLocalM.reset();
}

const SkMatrix& SkTouchGesture::localM() {
    if (fFlinger.isActive()) {
        if (!fFlinger.evaluateMatrix(&fLocalM)) {
            this->flushLocalM();
        }
    }
    return fLocalM;
}

void SkTouchGesture::appendNewRec(void* owner, float x, float y) {
    Rec* rec = fTouches.append();
    rec->fOwner = owner;
    rec->fStartX = rec->fPrevX = rec->fLastX = x;
    rec->fStartY = rec->fPrevY = rec->fLastY = y;
    rec->fLastT = rec->fPrevT = SkTime::GetMSecs();
}

void SkTouchGesture::touchBegin(void* owner, float x, float y) {
//    GrPrintf("--- %d touchBegin %p %g %g\n", fTouches.count(), owner, x, y);

    int index = this->findRec(owner);
    if (index >= 0) {
        this->flushLocalM();
        fTouches.removeShuffle(index);
        SkDebugf("---- already exists, removing\n");
    }

    if (fTouches.count() == 2) {
        return;
    }

    this->flushLocalM();
    fFlinger.stop();

    this->appendNewRec(owner, x, y);

    switch (fTouches.count()) {
        case 1:
            fState = kTranslate_State;
            break;
        case 2:
            fState = kZoom_State;
            break;
        default:
            break;
    }
}

int SkTouchGesture::findRec(void* owner) const {
    for (int i = 0; i < fTouches.count(); i++) {
        if (owner == fTouches[i].fOwner) {
            return i;
        }
    }
    return -1;
}

static float center(float pos0, float pos1) {
    return (pos0 + pos1) * 0.5f;
}

static const float MAX_ZOOM_SCALE = 4;
static const float MIN_ZOOM_SCALE = 0.25f;

float SkTouchGesture::limitTotalZoom(float scale) const {
    // this query works 'cause we know that we're square-scale w/ no skew/rotation
    const float curr = fGlobalM[0];
    
    if (scale > 1 && curr * scale > MAX_ZOOM_SCALE) {
        scale = MAX_ZOOM_SCALE / curr;
    } else if (scale < 1 && curr * scale < MIN_ZOOM_SCALE) {
        scale = MIN_ZOOM_SCALE / curr;
    }
    return scale;
}

void SkTouchGesture::touchMoved(void* owner, float x, float y) {
//    GrPrintf("--- %d touchMoved %p %g %g\n", fTouches.count(), owner, x, y);

    SkASSERT(kEmpty_State != fState);

    int index = this->findRec(owner);
    if (index < 0) {
        // not found, so I guess we should add it...
        SkDebugf("---- add missing begin\n");
        this->appendNewRec(owner, x, y);
        index = fTouches.count() - 1;
    }

    Rec& rec = fTouches[index];

    // not sure how valuable this is
    if (fTouches.count() == 2) {
        if (close_enough_for_jitter(rec.fLastX, rec.fLastY, x, y)) {
//            GrPrintf("--- drop touchMove, withing jitter tolerance %g %g\n", rec.fLastX - x, rec.fLastY - y);
            return;
        }
    }

    rec.fPrevX = rec.fLastX; rec.fLastX = x;
    rec.fPrevY = rec.fLastY; rec.fLastY = y;
    rec.fPrevT = rec.fLastT; rec.fLastT = SkTime::GetMSecs();

    switch (fTouches.count()) {
        case 1: {
            float dx = rec.fLastX - rec.fStartX;
            float dy = rec.fLastY - rec.fStartY;
            dx = (float)sk_float_round2int(dx);
            dy = (float)sk_float_round2int(dy);
            fLocalM.setTranslate(dx, dy);
        } break;
        case 2: {
            SkASSERT(kZoom_State == fState);
            const Rec& rec0 = fTouches[0];
            const Rec& rec1 = fTouches[1];
            
            float scale = this->computePinch(rec0, rec1);
            scale = this->limitTotalZoom(scale);

            fLocalM.setTranslate(-center(rec0.fStartX, rec1.fStartX),
                                 -center(rec0.fStartY, rec1.fStartY));
            fLocalM.postScale(scale, scale);
            fLocalM.postTranslate(center(rec0.fLastX, rec1.fLastX),
                                  center(rec0.fLastY, rec1.fLastY));
        } break;
        default:
            break;
    }
}

void SkTouchGesture::touchEnd(void* owner) {
//    GrPrintf("--- %d touchEnd   %p\n", fTouches.count(), owner);

    int index = this->findRec(owner);
    if (index < 0) {
        SkDebugf("--- not found\n");
        return;
    }

    const Rec& rec = fTouches[index];
    if (this->handleDblTap(rec.fLastX, rec.fLastY)) {
        return;
    }

    // count() reflects the number before we removed the owner
    switch (fTouches.count()) {
        case 1: {
            this->flushLocalM();
            float dx = rec.fLastX - rec.fPrevX;
            float dy = rec.fLastY - rec.fPrevY;
            float dur = (rec.fLastT - rec.fPrevT) * 0.001f;
            if (dur > 0) {
                fFlinger.reset(dx / dur, dy / dur);
            }
            fState = kEmpty_State;
        } break;
        case 2:
            this->flushLocalM();
            SkASSERT(kZoom_State == fState);
            fState = kEmpty_State;
            break;
        default:
            SkASSERT(kZoom_State == fState);
            break;
    }

    fTouches.removeShuffle(index);
}

float SkTouchGesture::computePinch(const Rec& rec0, const Rec& rec1) {
    double dx = rec0.fStartX - rec1.fStartX;
    double dy = rec0.fStartY - rec1.fStartY;
    double dist0 = sqrt(dx*dx + dy*dy);

    dx = rec0.fLastX - rec1.fLastX;
    dy = rec0.fLastY - rec1.fLastY;
    double dist1 = sqrt(dx*dx + dy*dy);

    double scale = dist1 / dist0;
    return (float)scale;
}

bool SkTouchGesture::handleDblTap(float x, float y) {
    bool found = false;
    SkMSec now = SkTime::GetMSecs();
    if (now - fLastUpT <= MAX_DBL_TAP_INTERVAL) {
        if (SkPoint::Length(fLastUpP.fX - x,
                            fLastUpP.fY - y) <= MAX_DBL_TAP_DISTANCE) {
            fFlinger.stop();
            fLocalM.reset();
            fGlobalM.reset();
            fTouches.reset();
            fState = kEmpty_State;
            found = true;
        }
    }

    fLastUpT = now;
    fLastUpP.set(x, y);
    return found;
}