Another time source for QML animations? - qt

Question

I am thinking about building a gstreamer plugin that renders animated QML graphics for later overlaying onto playing video. So far the idea to use QML looks very promising to me, except one problem. I need to be able to seek within the video, and the animations must also rewind and jump to the required point in time. Now that I read QML docs, I see that all the animations are typically time bound.
So my question is: is it possible to bind QML animations to some "time source", other than the real world time, which may not be monotonous (in fact, it can be manipulated by the application). Or, more generically, can I bind QML animation to a numeric value X, so that when it changes, my animation progresses, and there is a strict relation between X and animation state. I hope you get the idea.

Answer 1

This answer is suitable only for NumberAnimation object. Probably similar approach can be used to replace other Animation objects as well.
As already stated by ddriver there is no other way than work around.
Here is my solution to the problem. It may seem complicated but I can assure it is easy to use. At the end of this answer I put a link to the source code of example project using this code. You can try it.
Add these files to your project:
easingvalueforprogress.h
#ifndef EASINGVALUEFORPROGRESS_H
#define EASINGVALUEFORPROGRESS_H
#include <QObject>
#include <QEasingCurve>
class EasingValueForProgress : public QObject
{
Q_OBJECT
public:
explicit EasingValueForProgress(QObject *parent = 0);
Q_INVOKABLE double getValue(int easingEnum, double progress){
QEasingCurve easing((QEasingCurve::Type)easingEnum);
return easing.valueForProgress(progress);
}
signals:
public slots:
};
#endif // EASINGVALUEFORPROGRESS_H
easingvalueforprogress.cpp
#include "easingvalueforprogress.h"
EasingValueForProgress::EasingValueForProgress(QObject *parent) : QObject(parent)
{
}
XValueAnimation.qml
import QtQuick 2.0
Item {
id: xValueAnimator
property Item target
property string targetProperty
property double from
property double to
property int easing: Easing.Linear
property double xValue
onXValueChanged: {
if (target.hasOwnProperty(targetProperty)) {
target[targetProperty] = calculateCurrentValue(
from, to, easing, xValue);
}
else
console.error("XValueAnimator: target:", target,
"does not have property", targetProperty)
}
function calculateCurrentValue(
defaultFrom, defaultTo, animationEasing, xValue) {
return defaultFrom + (defaultTo - defaultFrom)
* easingValueForProgress.getValue(animationEasing, xValue)
}
}
Add this to your main.cpp:
#include <QQmlContext>
#include "easingvalueforprogress.h"
EasingValueForProgress easingValueForProgress;
engine.rootContext()->setContextProperty(
"easingValueForProgress", &easingValueForProgress);
Now you can use it like this (instead of NumberAnimation object):
XValueAnimator {
target: object_you_want_to_affect // for example id of the object
targetProperty: "property_to_affect" // for example "x"
from: 100
to: 500
easing: Easing.OutQuad // omit to use Easing.Linear
xValue: myXValue // your property holding values from 0 to 1
}
Here I provided working example project. Feel free to download and test it.