Fastest code changing pixels in Qt for animation - c++

Question

I want to animate small (100x20) image by changing the color of its pixels by the same value. For example, increase red-channel value by 1 every frame and then decrease back. The image has alpha channel, the animation speed is 30...100 fps (platform dependent; 30 is enough for linux, but windows requires ~70 to look smooth).
As i know, drawing is faster when done in QImage, but displaying is faster with QPixmap.

Answer 1

I like QGraphicsEffects, and QPropertyAnimations. White doesn't colorize, but black does.
#include <QLabel>
#include <QPixmap>
#include <QGraphicsColorizeEffect>
#include <QTimerEvent>
#include <QPropertyAnimation>
#include <QShowEvent>
#include <QDebug>
class Widget : public QLabel
{
Q_OBJECT
Q_PROPERTY(qreal redness READ getRedness WRITE setRedness)
public:
Widget(QWidget *parent = 0)
{
QPixmap p(300, 300);
p.fill(Qt::black);
this->setPixmap(p);
colorize = new QGraphicsColorizeEffect();
colorize->setColor(Qt::red);
redness = 0;
colorize->setStrength(redness);
this->setGraphicsEffect(colorize);
animation = new QPropertyAnimation(this,"redness");
animation->setDuration(2000);
animation->setLoopCount(10);
animation->setStartValue(0.0);
animation->setEndValue(1.0);
animation->setEasingCurve(QEasingCurve::CosineCurve);
animation->start();
}
~Widget(){}
qreal getRedness()
{
return redness;
}
void setRedness(qreal val)
{
redness = val;
colorize->setStrength(redness);
this->update();
// qDebug() << redness;
}
public slots:
void showEvent(QShowEvent *)
{
animation->start();
}
private:
qreal redness;
QGraphicsColorizeEffect * colorize;
QPropertyAnimation * animation;
};
and here is the main.cpp
#include <QApplication>
#include "widget.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget w;
w.show();
return a.exec();
}
Hope that helps.