QEasingCurve how to get progress for value?

[Mechan]

Hi,
I'm trying to get linear progress from eased value of QEasingCurve, i.e. basically inverse function for valueForProgress. I could do that by inversing equations from functions in src/3rdparty/easing/easing.cpp, but maybe there is simpler way?

What i'm trying to do is an animation which has different easing curves for different directions (Forward/Backward), but it's direction can be changed while animation is in progress. When I just do:

QPropertyAnimation *anim = new QPropertyAnimation(this, "pos");
 
    (...)
 
if(dir == AnimateIn){
    anim->setEasingCurve(QEasingCurve::OutExpo);
    anim->setDirection(QAbstractAnimation::Forward);
} else if(dir == AnimateOut){
    anim->setEasingCurve(QEasingCurve::InExpo);
    anim->setDirection(QAbstractAnimation::Backward);
}

QPropertyAnimation *anim = new QPropertyAnimation(this, "pos");

    (...)

if(dir == AnimateIn){
    anim->setEasingCurve(QEasingCurve::OutExpo);
    anim->setDirection(QAbstractAnimation::Forward);
} else if(dir == AnimateOut){
    anim->setEasingCurve(QEasingCurve::InExpo);
    anim->setDirection(QAbstractAnimation::Backward);
}

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value is diferrent for the same progress in different easing curves, so animation is rough.


With progressForValue function I could do something like that:

QEasingCurve oldCurve = anim->easingCurve();
int time = anim->currentTime();
if(dir == AnimateIn){
    anim->setEasingCurve(QEasingCurve::OutExpo);
    anim->setDirection(QAbstractAnimation::Forward);
} else if(dir == AnimateOut){
    anim->setEasingCurve(QEasingCurve::InExpo);
    anim->setDirection(QAbstractAnimation::Backward);
}
 
int duration = anim->duration();
qreal progress = ((duration == 0) ? 1 : ((((time - 1) % duration) + 1) / qreal(duration)));
 
qreal newProgress = anim->easingCurve().progressForValue(oldCurve.valueForProgress(progress));
 
anim->setCurrentTime(duration * newProgress);

QEasingCurve oldCurve = anim->easingCurve();
int time = anim->currentTime();
if(dir == AnimateIn){
    anim->setEasingCurve(QEasingCurve::OutExpo);
    anim->setDirection(QAbstractAnimation::Forward);
} else if(dir == AnimateOut){
    anim->setEasingCurve(QEasingCurve::InExpo);
    anim->setDirection(QAbstractAnimation::Backward);
}

int duration = anim->duration();
qreal progress = ((duration == 0) ? 1 : ((((time - 1) % duration) + 1) / qreal(duration)));

qreal newProgress = anim->easingCurve().progressForValue(oldCurve.valueForProgress(progress));

anim->setCurrentTime(duration * newProgress);

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Any suggestions?