michael@0: 
michael@0: /*
michael@0:  * Copyright 2010 Google Inc.
michael@0:  *
michael@0:  * Use of this source code is governed by a BSD-style license that can be
michael@0:  * found in the LICENSE file.
michael@0:  */
michael@0: 
michael@0: 
michael@0: 
michael@0: #include "FlingState.h"
michael@0: #include "SkMatrix.h"
michael@0: #include "SkTime.h"
michael@0: 
michael@0: #define DISCRETIZE_TRANSLATE_TO_AVOID_FLICKER   true
michael@0: 
michael@0: static const float MAX_FLING_SPEED = 1500;
michael@0: 
michael@0: static float pin_max_fling(float speed) {
michael@0:     if (speed > MAX_FLING_SPEED) {
michael@0:         speed = MAX_FLING_SPEED;
michael@0:     }
michael@0:     return speed;
michael@0: }
michael@0: 
michael@0: static double getseconds() {
michael@0:     return SkTime::GetMSecs() * 0.001;
michael@0: }
michael@0: 
michael@0: // returns +1 or -1, depending on the sign of x
michael@0: // returns +1 if x is zero
michael@0: static SkScalar SkScalarSign(SkScalar x) {
michael@0:     SkScalar sign = SK_Scalar1;
michael@0:     if (x < 0) {
michael@0:         sign = -sign;
michael@0:     }
michael@0:     return sign;
michael@0: }
michael@0: 
michael@0: static void unit_axis_align(SkVector* unit) {
michael@0:     const SkScalar TOLERANCE = SkDoubleToScalar(0.15);
michael@0:     if (SkScalarAbs(unit->fX) < TOLERANCE) {
michael@0:         unit->fX = 0;
michael@0:         unit->fY = SkScalarSign(unit->fY);
michael@0:     } else if (SkScalarAbs(unit->fY) < TOLERANCE) {
michael@0:         unit->fX = SkScalarSign(unit->fX);
michael@0:         unit->fY = 0;
michael@0:     }
michael@0: }
michael@0: 
michael@0: void FlingState::reset(float sx, float sy) {
michael@0:     fActive = true;
michael@0:     fDirection.set(sx, sy);
michael@0:     fSpeed0 = SkPoint::Normalize(&fDirection);
michael@0:     fSpeed0 = pin_max_fling(fSpeed0);
michael@0:     fTime0 = getseconds();
michael@0: 
michael@0:     unit_axis_align(&fDirection);
michael@0: //    printf("---- speed %g dir %g %g\n", fSpeed0, fDirection.fX, fDirection.fY);
michael@0: }
michael@0: 
michael@0: bool FlingState::evaluateMatrix(SkMatrix* matrix) {
michael@0:     if (!fActive) {
michael@0:         return false;
michael@0:     }
michael@0: 
michael@0:     const float t =  getseconds() - fTime0;
michael@0:     const float MIN_SPEED = 2;
michael@0:     const float K0 = 5.0;
michael@0:     const float K1 = 0.02;
michael@0:     const float speed = fSpeed0 * (sk_float_exp(- K0 * t) - K1);
michael@0:     if (speed <= MIN_SPEED) {
michael@0:         fActive = false;
michael@0:         return false;
michael@0:     }
michael@0:     float dist = (fSpeed0 - speed) / K0;
michael@0: 
michael@0: //    printf("---- time %g speed %g dist %g\n", t, speed, dist);
michael@0:     float tx = fDirection.fX * dist;
michael@0:     float ty = fDirection.fY * dist;
michael@0:     if (DISCRETIZE_TRANSLATE_TO_AVOID_FLICKER) {
michael@0:         tx = sk_float_round2int(tx);
michael@0:         ty = sk_float_round2int(ty);
michael@0:     }
michael@0:     matrix->setTranslate(tx, ty);
michael@0: //    printf("---- evaluate (%g %g)\n", tx, ty);
michael@0: 
michael@0:     return true;
michael@0: }
michael@0: 
michael@0: ////////////////////////////////////////
michael@0: 
michael@0: GrAnimateFloat::GrAnimateFloat() : fTime0(0) {}
michael@0: 
michael@0: void GrAnimateFloat::start(float v0, float v1, float duration) {
michael@0:     fValue0 = v0;
michael@0:     fValue1 = v1;
michael@0:     fDuration = duration;
michael@0:     if (duration > 0) {
michael@0:         fTime0 = SkTime::GetMSecs();
michael@0:         if (!fTime0) {
michael@0:             fTime0 = 1;  // time0 is our sentinel
michael@0:         }
michael@0:     } else {
michael@0:         fTime0 = 0;
michael@0:     }
michael@0: }
michael@0: 
michael@0: float GrAnimateFloat::evaluate() {
michael@0:     if (!fTime0) {
michael@0:         return fValue1;
michael@0:     }
michael@0: 
michael@0:     double elapsed = (SkTime::GetMSecs() - fTime0) * 0.001;
michael@0:     if (elapsed >= fDuration) {
michael@0:         fTime0 = 0;
michael@0:         return fValue1;
michael@0:     }
michael@0: 
michael@0:     double t = elapsed / fDuration;
michael@0:     if (true) {
michael@0:         t = (3 - 2 * t) * t * t;
michael@0:     }
michael@0:     return fValue0 + t * (fValue1 - fValue0);
michael@0: }