How to draw a Qgraphicsitem on a Qimage?

[d_stranz]

@thinker: I am not clear on exactly *what* it is that you want your users to be able to flood fill - the graphical items they have added, the background, what? You should think about composing your scene in layers, by using the z-value property of graphics items. Items with a higher z-value will clip items with lower z-value (ignoring transparency for now), so in essence the scene will do all of the work needed to calculate intersections and such. Whatever you want to flood fill should have a lower z-value than the things on top.

I agree with Wysota - you are going about this totally backward if you think that -you- need to convert your scene to an image and do all the work of filling flooded areas yourself. All the tools are there in the Graphics / View architecture, you just need to learn how to use them.

[eternalthinker]

@thinker: I am not clear on exactly *what* it is that you want your users to be able to flood fill - the graphical items they have added, the background, what?

Think about flood filling in a typical drawing application - this case is just the same.

So users might draw circles, rectangles, and free hand curves which are not closed.
And a flood fill might fill a complex closed shape made by free hand lines, or leak out of an open shape and fill the whole background.

And user might really click anywhere, not just on the lower z valued items. May be on the very lines themselves!

[wysota]

Does the fill create a new object or modify existing ones?

[eternalthinker]

Does the fill create a new object or modify existing ones?

It can be done either way, depending upon what supports the logic better.
The aim here is just to create floodfill. So a new object can be created if required!

[wysota]

There's a fundamental difference between the two. If you don't care about it then maybe you shouldn't be using graphics view at all? If you're just after raster painting then there are no benefits in using graphics view and you can reduce your implementation to a widget displaying QPixmap/QImage.

[eternalthinker]

There's a fundamental difference between the two. If you don't care about it then maybe you shouldn't be using graphics view at all? If you're just after raster painting then there are no benefits in using graphics view and you can reduce your implementation to a widget displaying QPixmap/QImage.

As I have mentioned in the question, the most recent item is editable by the user.
ie, it can be dragged around, resized and rotated before the final permamnent version is drawn.
I thought this could be easier to implement with QGraphicsView

[wysota]

As I have mentioned in the question, the most recent item is editable by the user.
ie, it can be dragged around, resized and rotated before the final permamnent version is drawn.
I thought this could be easier to implement with QGraphicsView

That doesn't require graphics view. Nevertheless my question still stands -- if your fill is to create a new "most recent item" that is to be "editable by the user" then it is much different from filling an existing item or canvas.

[eternalthinker]

That doesn't require graphics view. Nevertheless my question still stands -- if your fill is to create a new "most recent item" that is to be "editable by the user" then it is much different from filling an existing item or canvas.

Actually 'editable' apply to only a selected few items in the application. This excludes floodfills and freehand lines.