SkCanvas resize

[Anthony Catel]

Hey,

What's an easy way to resize a SkCanvas?
I was using SkCanvas::setDevice with a new sized canvas but this method was deprecated.

For the moment I'm doing something like this : http://pastebin.com/vFSTedgy
The problem is that the new SkCanvas lost its "context" (i.e. current matrix, clip, saved stack, etc...).

Any advice?

Thanks ;-)

[Tom Hudson]

To back up a step, what is it that you're trying to do that you want to solve by resizing the canvas?

My first thought was to look at what SampleApp does when the window gets resized, but it's not obvious how the canvas changes (if at all) in that case; there are several layers of indirection through the Views hierarchy and virtual function overrides.

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[Anthony Catel]

My application is using skia (backed by a GL device) to draw its UI.
Every element of my UI is a SkCanvas (internally a FBO handled by skia).
I have a case where I have something like a "UIWindow" which is resizable by the user. When it's resized I just have to resize the SkCanvas (and thus avoiding to redraw everything behind). I know it's an heavy process (create a new FBO, copy the old one, etc...) but it's still faster than having to redraw everything behind the UIWindow.

Do you see any better solution?

Thanks

[Mike Reed]

Resizing the backing pixels (cpu or gpu) is fine, though up to you. From Skia's perspective, a new device size requires a new canvas(+device). SkCanvas is just a drawing statemachine on top of your pixels, so it should not be too expensive to create a brand new canvas that points at your (old or new) pixels.

To view this discussion on the web visit https://groups.google.com/d/msg/skia-discuss/-/wYCTqWpVUQAJ.

[Brian Salomon]

I think the problem Anthony is running up against is copying the state from the old canvas to the new canvas. 

[Anthony Catel]

Mike, That's what I already do, and it works just fine.
Brian is right, what I'm looking for is a replacement for SkCanvas::setDevice(). That is, copy the old SkCanvas state.

[Mike Reed]

Gotcha.

No perfect way to replicate canvas state today.

new.clipRegion(old.getTotalClip())

new.setMatrix(old.getTotalMatrix())

These might get you close, but they don't 

- handle aa clips

- preserve save/restore information

- don't play friendly w/ GPU backend on non-rectangular clips

To view this discussion on the web visit https://groups.google.com/d/msg/skia-discuss/-/lEmB5ynyP80J.

[Anthony Catel]

Ok thanks, that's what I thought. Will try to work on a SkCanvas replication solution then. 

Btw, what was the reason for having marked SkCanvas::setDevice as deprecated?

A.

[Mike Reed]

Pretty much for this reason: changing the device (subclass and/or dimensions) can be hard/impossible for the canvas to update its state perfectly. We are moving towards making SkDevice itself an implementation-only class hierarchy, and not visible to the client. Look at SkSurface.h and SkImage.h to see a glimpse of the future!

[Janez Zemva]

Will writing a custom SkDevice still be possible?

2013/1/17 Mike Reed <re...@google.com>:

[Mike Reed]

... probably. Certainly the SkCanvas constructor that takes a device will last a long time. Part of the value of hiding SkDevice is to make it easier for us to modify its interface for performance reasons, as we continue to work on raster/gpu/pdf/picture/etc. backends.

[a.c...@weelya.com]

It makes sense.
Thanks for the insight.

>> >>>>>>>> http://pastebin.com/vFSTedgy [1]

>> >>>>>>>> The problem is that the new SkCanvas lost its "context"
>> (i.e.
>> >>>>>>>> current matrix, clip, saved stack, etc...).
>> >>>>>>>>
>> >>>>>>>> Any advice?
>> >>>>>>>>
>> >>>>>>>> Thanks ;-)
>> >>>>>>>>
>> >>>>>>>> --
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>> >>>>>>>> Groups "skia-discuss" group.
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>> >>>>>>>> https://groups.google.com/d/msg/skia-discuss/-/hsQ_gWfbU90J

>> [2].

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> Links:
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> [1] http://pastebin.com/vFSTedgy
> [2] https://groups.google.com/d/msg/skia-discuss/-/hsQ_gWfbU90J
> [3] http://groups.google.com/group/skia-discuss?hl=en
> [4] https://groups.google.com/d/msg/skia-discuss/-/wYCTqWpVUQAJ
> [5] https://groups.google.com/d/msg/skia-discuss/-/lEmB5ynyP80J