Scaling QImage ( zooming ) and drawing slowes down the performance

[sanjayshelke]

Hi all,

I am developing small application which can edit image.That is it has Zoom and Erase functionality.

I am facing performance issue when i zoom the image and starts erasing it.

Zoom functionality is implemented by scaled() API of QImage and erase functionality is implemented by drawing on the scaled image with CompositionMode set to QPainter::CompositionMode_Clear.

How MSPAINT application does the same task smoothley.

Is there any way to improve the performance?

Thanks in advance

Regards,
~Sanjay

[wysota]

We'd have to see the exact code. I'm assuming you are converting between QImage and QPixmap all the time and this is slow.

[sanjayshelke]

Very true.

I am converting it from QPixmap to QImage.And then erased image using QPainter.
After done erasing converting to QPixmap again.

like this :

QImage imgPixmap(m_imgViewer->pixmap()->toImage());
 
	QPainter painter(&imgPixmap);
	painter.setCompositionMode(QPainter::CompositionMode_Clear);
	QPen pen;
	pen.setCapStyle(Qt::RoundCap);
	pen.setWidth(m_nEraserSize);
	painter.setPen(pen);
	painter.drawPoint(ptPos);
	painter.end();
 
       m_imgViewer->setPixmap(QPixmap::fromImage(imgPixmap));	// show the image
       m_imgViewer->setMinimumSize(m_imgViewer->pixmap()->size());

QImage imgPixmap(m_imgViewer->pixmap()->toImage());

	QPainter painter(&imgPixmap);
	painter.setCompositionMode(QPainter::CompositionMode_Clear);
	QPen pen;
	pen.setCapStyle(Qt::RoundCap);
	pen.setWidth(m_nEraserSize);
	painter.setPen(pen);
	painter.drawPoint(ptPos);
	painter.end();

       m_imgViewer->setPixmap(QPixmap::fromImage(imgPixmap));	// show the image
       m_imgViewer->setMinimumSize(m_imgViewer->pixmap()->size());

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Note : m_imgViewer is a QLabel.

Any idea how to do that.

Regards,
~Sanjay

[wysota]

How about having two pixmaps - one is the base image and the other is a mask that you will apply to the image when saving it. Then you don't have to convert the base pixmap, just operate on the upper "layer".

A simpler solution is to paint directly on the pixmap, you don't have to convert it to QImage before doing so.

[sanjayshelke]

Very sorry.
I am late to reply.
yes i tried painting directly on QPixmap and it works.

Thank you.


regards,
~Sanjay