Sample code for rotating

depecheSoul

Hello.

I am trying to make a simple example of rotating houses that I saw at this video: http://qt-project.org/videos/watch/advanced-qt-a-deep-dive-1-6-graphics-view-1 from 56:36.

Can you please tell me is there any written form to that of similar code that I can look at. I tried to find any examples of that code because I learn the best when I look at some code, and in the video I cant do this.

Thanks

DerManu

All "QGraphicsView examples":http://doc-snapshot.qt-project.org/4.8/examples-graphicsview.html might help you.
If you're only looking for the perspective rotaton effect, see QTransform, and set a rotation that's not around the Z axis but e.g. X or Y. When QGraphicsView gets Rotations like that, it fakes a 3D effect by stretching/shearing the rotated objects.

zakarrrr

Trick at this point is to move the rect to (0, 0) and then rotate:

@class Widget : public QWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = 0) { }

void paintEvent(QPaintEvent * event);

};

void Widget::paintEvent(QPaintEvent * event)
{
//rotate a rect around its middle point
QPainter painter(this);

QRect rect(150, 150, 200, 100);
painter.drawRect(rect);
painter.drawPoint(rect.center());

// this is hard-coded : the middle point of the rect is now real (0, 0) of painter's default window system
QRect rect2(-100, -50, 200, 100);
painter.translate(250, 200);

static qreal degree = 0;
painter.rotate(degree++);
painter.drawRect(rect2);
painter.drawPoint(rect2.center());

QTimer::singleShot(1, this, SLOT(update()));

}@

zakarrrr

But if you want to rotate the point by yourself (which wont be easy), you can do something like this : ( hope helps :) )

@void Widget::paintEvent(QPaintEvent * event)
{
QPainter painter(this);
static qreal degree = 0;

QLine line(QPoint(100, 100), QPoint(199, 199));
QPoint origin;
origin.setX((line.p1().x() + line.p2().x())/2);
origin.setY((line.p1().y() + line.p2().y())/2);

painter.drawLine(line);

// rotate point 1
QPoint ptRotated1 = rotatePoint(degree, origin, line.p1());
QPoint ptRotated2 = rotatePoint(degree, origin, line.p2());

painter.drawLine(QLine(ptRotated1, ptRotated2));

++degree;

QTimer::singleShot(1, this, SLOT(update()));

}

QPoint Widget::rotatePoint(int degree, QPoint origin, QPoint ptRotate) {

double Pi = 3.14159265358979323846264338327950288419717;
double rotAngle = degree * (Pi / 180.0);
double sinAngle = qSin(rotAngle);
double cosAngle = qCos(rotAngle);

int px = ptRotate.x() - origin.x();
int py = ptRotate.y() - origin.y();

float xnew = px * cosAngle + py * sinAngle;
float ynew = py * cosAngle - px * sinAngle;

px = xnew + origin.x();
py = ynew + origin.y();

return QPoint(px, py);

}@