adding text values on top of pixels in ImageItem

[Kuba Raczkowski]

Hi,

I'm trying to annotate the ImageItem's pixels by a textual value on top of every pixel. 

Got it working by extending the paint() and adding necessary drawText() calls, however, the performance is (obviously?) terrible.

This is only meant to be useful when zooming in deeply - that I can treshold by figuring out pixelSize() of ImageItem.

However, all labels seem to be painted even if only a few pixels are visible in the view. 

Any idea how to figure out the pixels (or a rectangle) that are actually visible in the view? I'm getting lost in all the coordinate mappings :/

Best regards,

Kuba

[Kuba Raczkowski]

Ok, well, managed to do it based on https://stackoverflow.com/questions/4763992/finding-out-what-portion-of-a-qgraphicsitem-is-visible-in-a-qgraphicsview#

FYI, this gives a visible rectangle inside an imageitem, in its coordinates:

            view = self.getViewBox().getViewWidget()

            portRect = view.viewport().rect()

            sceneRect = view.mapToScene(portRect).boundingRect()

            itemRect = self.mapRectFromScene(sceneRect)

            isec = itemRect.intersected(self.boundingRect())

Kuba

[Luke Campagnola]

In the past I have used QGraphicsTextItem with a monospace font for displaying grids of characters.

That should yield good performance, depending on the size of your image.

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[Kuba]

Thanks for reply Luc! 

Any thoughs on whether using QGraphicsTextItem would be preferable to modifying the paint() of ImageItem?

Kuba

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