2 Questions about QPainter

[SkripT]

Hi, relating to my question number 1, I've tried different Composition Modes but the result is always the same: the surface where I paint is always cleared, so only appears what I've painted on the last time Here's a simplified version of the code that I use:

void FotoEditorFotos::paintEvent(QPaintEvent *event)
{
	QPainter painter;
	painter.begin(this);
 
	if (rectABorrar.isNull())
	{
                          // Paint all the image for the first time centered on the widget
		int rectW = arrodonirValor(imatge.width() * escala);
		int rectH = arrodonirValor(imatge.height() * escala);
		rectFoto.setRect((width() >> 1) - (rectW >> 1), (height() >> 1) - (rectH >> 1), rectW, rectH);
 
		painter.drawImage(rectFoto, imatge);
	}
	else
	{
                 // "rectSeleccio" defines the old position and size (geometry) of the rubberband and needs to be deleted with the original portion of the image, defined by "rectABorrar"
		painter.setCompositionMode(QPainter::CompositionMode_Destination);//I don't know if this is the Composition Mode that I should use????
		painter.drawImage(rectSeleccio, imatge, rectABorrar);
 
		rectABorrar.setRect(-1, -1, 0, 0);
	}
 
    // Code to Paint the rubberband.........
 
       painter.end()
}

void FotoEditorFotos::paintEvent(QPaintEvent *event)
{
	QPainter painter;
	painter.begin(this);

	if (rectABorrar.isNull())
	{
                          // Paint all the image for the first time centered on the widget
		int rectW = arrodonirValor(imatge.width() * escala);
		int rectH = arrodonirValor(imatge.height() * escala);
		rectFoto.setRect((width() >> 1) - (rectW >> 1), (height() >> 1) - (rectH >> 1), rectW, rectH);

		painter.drawImage(rectFoto, imatge);
	}
	else
	{
                 // "rectSeleccio" defines the old position and size (geometry) of the rubberband and needs to be deleted with the original portion of the image, defined by "rectABorrar"
		painter.setCompositionMode(QPainter::CompositionMode_Destination);//I don't know if this is the Composition Mode that I should use????
		painter.drawImage(rectSeleccio, imatge, rectABorrar);

		rectABorrar.setRect(-1, -1, 0, 0);
	}

    // Code to Paint the rubberband.........

       painter.end()
}

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Anybody could tell me where's the mistake? Thanks.