Rotation problem trying to draw a compass widget

[yellowmat]

Hi everybody,

I am developping a custom widget, a compass, composed of a background pixmap and a foreground pixmap (the cursor).

My paintEvent code is a s follow :

QPainter painter(this);
 
	painter.drawPixmap(0, 0, *m_pBackground);
	painter.rotate(m_dAngle);
	painter.drawPixmap(0, 0, *m_pForeground);

QPainter painter(this);

	painter.drawPixmap(0, 0, *m_pBackground);
	painter.rotate(m_dAngle);
	painter.drawPixmap(0, 0, *m_pForeground);

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The problem here is that after being rotated, the foreground pixmap is not centered over the background pixmap center.

I think I must code something like this :

QPainter painter(this);
 
	painter.drawPixmap(0, 0, *m_pBackground);
	painter.rotate(m_dAngle);
                painter.translate(x, y);
	painter.drawPixmap(0, 0, *m_pForeground);

QPainter painter(this);

	painter.drawPixmap(0, 0, *m_pBackground);
	painter.rotate(m_dAngle);
                painter.translate(x, y);
	painter.drawPixmap(0, 0, *m_pForeground);

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but how to determine x and y ?

It would be great if anybody could give me a clue.

Thanks in advance.

[jacek]

I think I must code something like this :
...
but how to determine x and y ?

Try:

int x = m_pBackground->width() / 2;  // or width() if it's the same
int y = m_pBackground->height() / 2;
 
painter.drawPixmap(0, 0, *m_pBackground);
 
painter.translate(-x, -y);
painter.rotate(m_dAngle);
painter.translate(x, y);
 
painter.drawPixmap(0, 0, *m_pForeground);

int x = m_pBackground->width() / 2;  // or width() if it's the same
int y = m_pBackground->height() / 2;

painter.drawPixmap(0, 0, *m_pBackground);

painter.translate(-x, -y);
painter.rotate(m_dAngle);
painter.translate(x, y);

painter.drawPixmap(0, 0, *m_pForeground);

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[yellowmat]

It works fine.

Thanks