QT QGraphicsItemAnimation - c++

Question

I've got a class: mySquare which inherits from QGraphicsRectItem
added only my constructor, painter and an animation:
ANIMATION:
void mySquare::animation(mySquare *k)
{
QTimeLine *timeLine = new QTimeLine();
timeLine->setLoopCount(1);
QGraphicsItemAnimation *animation = new QGraphicsItemAnimation();
animation->setItem(k);
animation->setTimeLine(timeLine);
int value = 30;
animation->setTranslationAt(0.3, value, value);
timeLine->start();
// (*)
// x += 30;
// y += 30;
}
PAINTER:
void Klocek::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *widget)
{
bokKwadratu = (min(widget->width(), widget->height()))/5;
setRect(x * 30, y * 30, 30 - 3, 30 - 3);
QRectF rect = boundingRect();
painter->setBrush(brush);
painter->setPen(pen);
QFont font;
font.setPixelSize(bokKwadratu/3);
painter->setFont(font);
painter->drawRect(rect);
painter->drawText(rect,Qt::AlignCenter, QString::number(wartosc));
}
CONSTRUCTOR:
mySquare::mySquare(qreal x, qreal y) : QGraphicsRectItem(x * 10, y * 10, 10, 10)
{
setAcceptHoverEvents(true);
this->x = x;
this->y = y;
pen.setColor(Qt::red);
pen.setWidth(2);
brush.setColor(Qt::blue);
brush.setStyle(Qt::SolidPattern);
}
after performing animation (translation) I need to change the object coordinates so they are compatible which the situation on the screen. In other words after the translation (30, 30) I want the coordinates of the rectangle to be change (x += 30, y += 30)
my problem is that when i try to do this ( (*) fragment in the code) the triangle is put far away from its position (just as if the translation was performed twice)
My question is how to translate it and change the coordinates without such complications.

Answer 1

To begin with, I think you're misunderstanding the use of the function setTranslationAt in the QGraphicsItem Animation.
An animation has a normalised value over time, so can start at 0.0 and end at 1.0 (or the reverse). Therefore, by calling
animation->setTranslationAt(0.3, value, value);
You've stated that at the point when the normalised value reaches 0.3, you want the x and y position to be set to 'value'. That's fine, but you also need to set other values for the animation to occur (especially at the val of 1.0!). If you use a for loop, you can iterate through values from 0.0 to 1.0 and set where you want the position of your item to be. Take a look at the example code in the Qt help files for QGraphicsItemAnimation. The QGraphicsItemAnimation uses interpolation to work out the position of your object between the known points that you've given it. If you're interested: -
http://en.wikipedia.org/wiki/Linear_interpolation
Secondly, the item's rect is the definition of the item in its local coordinate space. So if you wanted a rect with its axis in the centre, you'd define it with x,y,w,h of (-w/2, -h/2, w, h). As these are local coordinates, they then get mapped into world coordinates in the GraphicsScene, which is where you set its actual position in the world.
Once you've setup your QGraphicsItemRect's local coordinates and world position, you can then simply paint it with drawRect and should not be setting positions in the paint function.