Very Large Surface Woes.

[Corey Lucier]

I am trying to dynamically generate a very large retina (raster) image with Skia and a good portion of the canvas contents drawn is omitted from the final result.

The image itself in this case is exactly 21400 x 4000.  The contents up to about 16000 is visible, the remainder is not.

What is the actual raster surface/canvas limitation here I am hitting, and what would you recommend to solve this.  Even if I tile things in some way if I can't address > 16000 portion of my canvas how will I assemble the tiles for instance on my offscreen surface/canvas?

Thanks,

C

[Corey Lucier]

Actually, after further debugging... it seems that there might be a maximum clip rect?  In this case we have set a clip rect to bound the entire image and everything beyond the 16K point gets clipped. 

Also any sub-clip rects or clip shapes beyond the 16K point aren't showing up.

Bug that we should report or known limitation?

[Mike Reed]

Hmmmm

- gpu or cpu backend?

- show a snippet?

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[Mike Reed]

Ignore my prev -- didn't see this info.

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[Corey Lucier]

CPU.

I am trying to recreate with a fiddle but no luck.

If I dump a SKP file is there a skp dump utility that will show the skia calls I am making? (This is M69).  If I can do this I might be able to fine-tune my fiddle repro.

[Corey Lucier]

...a skip viewer that is for my skp file. I can generate the SKP file myself.

[Mike Klein]

Yes, we have an .skp debugger, which you can either use over the web at https://debugger.skia.org/ or build and yourself in the Skia tree (the binary is called skiaserve).

On Thu, Nov 1, 2018 at 12:21 PM Corey Lucier <corey....@gmail.com> wrote:

...a skip viewer that is for my skp file. I can generate the SKP file myself.

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[Mike Klein]

... or build and run yourself ...

[Corey Lucier]

So of course it doesn't repro in the Skia debugger... but at least I captured my steps.  See attached.

There must be something to explain not being able to clip beyond 16,384 (x or y).

[Corey Lucier]

So the debugger seems capped at 8k x 8k...so I can't use it to repro my issue per say.

[Corey Lucier]

In fact it's not showing my drawing calls (drawRect) in my SKP if I draw outside 8k.  Similar to problem I have in our app except that is capped at 16K.

[Corey Lucier]

OK, Finally reproduced.

https://fiddle.skia.org/c/ab0c5f4bb2ffec05677688566d30009a

If you change the position we draw the blue rect to anything over 16K it is clipped.

Rectangle clip masks work great..just not RRect or shape clips.

[Roman Petrenko]

I just ran into this issue too. Nothing is being drawn outside the (0,0 -> 16K,16K) bounds if you use clipping. Without clipping, things get drawn fine. Is there a way to work around this limitation?

Thanks in advance.

[Brian Salomon]

You might want to take a look at this discussion:

https://groups.google.com/d/msgid/skia-discuss/6caaacab-0776-4929-9c51-7cfe2782a5e0n%40googlegroups.com?utm_medium=email&utm_source=footer

The solution used there may work for you.

[Roman Petrenko]

Hi Brian, thanks for the advice. Yes, a tiling solution would help, but I'd like to point out that right now it's possible to create a surface having more than 16384 pixels in one dimension (for example, 20000*1000 pixels), and most of the drawing functionality will work fine, except cropping. So I think there is a bug in Skia related specifically to cropping.

[Brian Salomon]

Hi Roman,

Do you have an example you could share? Is it with any clip set?

Best,

Brian

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[Roman Petrenko]

Hi Brian,

The fiddle that was previously shared in this thread still reproduces the issue even though it's been 4 years: https://fiddle.skia.org/c/ab0c5f4bb2ffec05677688566d30009a

Best Regards,

Roman

[Michael Ludwig]

Hi Roman,

Skia fiddles don't re-compute their images, so that output was what's been saved since the fiddle was made. Making a white space change shows that the SkCanvas::drawBitmap API has been removed, and fixing that (https://fiddle.skia.org/c/b3376a02c819579bf2866288a9f05646) leads to a server sandbox violation, most likely trying to allocate the space for the very large bitmap.  I will try and run this locally and see if I can identify the cause.

[Mike Reed]

I've also been confused by 'stale' fiddle results.

I wonder if the cache could also include which skia version built the image -- so it would know it was stale on a re-run attempt.

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[Michael Ludwig]

I was able to reproduce this locally. It looks like SkRegion (which is used for handling the clip shape in this case) is not able to convert an SkPath with such large coordinates. It should be capable of representing it but there are some internal precision limits that it was running into. I have a bug here to track this work: https://bugs.chromium.org/p/skia/issues/detail?id=13626 but it'll be a little bit before I can tackle it.

Tiling at the SkCanvas level will bypass this and also allow you to take advantage of GPU canvases that have a more restricted image size already, so I would recommend pursuing that if you can.