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/*
* Copyright 2010 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "FlingState.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 FlingState::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 FlingState::evaluateMatrix(SkMatrix* matrix) {
if (!fActive) {
return false;
}
const float t = getseconds() - fTime0;
const float MIN_SPEED = 2;
const float K0 = 5.0;
const float K1 = 0.02;
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 = sk_float_round2int(tx);
ty = sk_float_round2int(ty);
}
matrix->setTranslate(tx, ty);
// printf("---- evaluate (%g %g)\n", tx, ty);
return true;
}
////////////////////////////////////////
GrAnimateFloat::GrAnimateFloat() : fTime0(0) {}
void GrAnimateFloat::start(float v0, float v1, float duration) {
fValue0 = v0;
fValue1 = v1;
fDuration = duration;
if (duration > 0) {
fTime0 = SkTime::GetMSecs();
if (!fTime0) {
fTime0 = 1; // time0 is our sentinel
}
} else {
fTime0 = 0;
}
}
float GrAnimateFloat::evaluate() {
if (!fTime0) {
return fValue1;
}
double elapsed = (SkTime::GetMSecs() - fTime0) * 0.001;
if (elapsed >= fDuration) {
fTime0 = 0;
return fValue1;
}
double t = elapsed / fDuration;
if (true) {
t = (3 - 2 * t) * t * t;
}
return fValue0 + t * (fValue1 - fValue0);
}
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