SkBitmap surface and multiple threads.

[Corey Lucier]

Is it feasible to write to one SkBitmap raster surface from multiple threads? If each owned a different quadrant for instance. Perhaps with one SkCanvas/Surface each owning a particular portion of the image?

Thanks,

Corey

[Mike Reed]

SkSurface and SkCanvas are both NOT thread-safe. Only SkImage and SkPicture are.

Thus to shard a large drawing across multiple threads, you need a separate instance of a surface/canvas in each thread.

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[Mike Klein]

Mike's right, but you can certainly have all those SkSurfaces point at the same backing pixel memory, using something like SkSurface::NewRasterDirect.

We're quite careful to never read or write outside the clip.

[Corey Lucier]

Yes conceptually I want a portion of my scene to an low-res offscreen layer using a thread pool...

Once complete, I want multiple threads to be able to render snippets from this offscreen in parallel as they see fit (no writing while reading).

So sounds like when everyone is working on this SkImage in a parallel (assuming they spin up a surface and canvas for the region they own), shouldn't be a problem.

-C