[Development] QPA / QWindow / QPainter

[Martin Koller]

On Monday 10 March 2014 14:43:42 Agocs Laszlo wrote:
> Yes, one platform window for each native widget and one backingstore per top level window. (where the toplevel's backingstore is the common backingstore for all of its child widgets)
> 
> QPA (QPlatformBackingStore) does not know anything about paint devices, paint engines and such. It allows you to provide a paint device to the widget stack or whoever performs the painting, that's all. The returned paint device could be a QImage, an OpenGL framebuffer object, a custom device with a custom paint engine doing stuff that has nothing to do with painting, etc. It does not have to be something that holds the actual pixels. The platform plugin must provide a backing store implementation however. (unless it does not care about widgets)
> 
> To implement your remoting use case, there is most likely no need to complicate things with native widgets. It is exactly the same concept as generating HTML5 canvas code or PDFs or anything else:
> 
> - Have a custom paint device that provides a custom paint engine which buffers the painting commands. Such a buffer will contain the drawing commands for all the children of a given toplevel.
> 
> - In the platform backingstore's flush send the commands over the network
> 
> Or is something, that would mandate the usage of native child widgets, missing from the picture here?

yes, I was trying to keep the explanation simple.
In fact what I do is to remote the painting commands to a HTML5 canvas, but as some objects shall do blinking,
which I do not want to be done via a lot of redraws, I instead create SVG objects which shall be intermixed displayed
with what the canvas shows (that is: primitve objects like lines, circles are SVG, widgets are drawn
as usual). But to have a chance that the stacking order of the SVG objects and the widgets is still
correct, I wanted to create the native widgets as separate canvas objects so that they do stack with the SVG objects.

What I think I can do to solve it is to use a global event filter, catch the paint events of the widgets I want to
stack correctly and redirect QWidget::render() to a paint device which knows the window id ... or something like that.

-- 
Best regards/Schöne Grüße

Martin
A: Because it breaks the logical sequence of discussion
Q: Why is top posting bad?

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