[whatwg] Canvas 2D memory management

[Justin Novosad]

On Fri, Jul 19, 2013 at 7:09 AM, Ashley Gullen <ashley at scirra.com> wrote:

> FWIW, imageBitmap.discard() wouldn't be unprecedented - WebGL allows you to
> explicitly release memory with deleteTexture() rather than letting the GC
> collect unused textures.
>
>
A related issue we have now is with canvas backing stores. It is common for
web apps to create temporary canvases to do some offscreen rendering. When
the temporary canvas goes out of scope, it continues to consume RAM or GPU
memory until it is garbage collected. Occasionally this results in
memory-leak-like symptoms.  The usual workaround is to use a single
persistent global canvas for offscreen work instead of temporary ones
(yuck).  This could be handled in a cleaner way if there were a .discard()
method on canvases elements too.


> Ashley
>
>
>
> On 18 July 2013 17:50, Ian Hickson <ian at hixie.ch> wrote:
>
> > On Wed, 9 Jan 2013, Ashley Gullen wrote:
> > >
> > > Some developers are starting to design large scale games using our
> HTML5
> > > game engine, and we're finding we're running in to memory management
> > > issues.  Consider a device with 50mb of texture memory available.  A
> > > game might contain 100mb of texture assets, but only use a maximum of
> > > 30mb of them at a time (e.g. if there are three levels each using 30mb
> > > of different assets, and a menu that uses 10mb of assets).  This game
> > > ought to fit in memory at all times, but if a user agent is not smart
> > > about how image loading is handled, it could run out of memory.
> > >
> > > [...]
> > >
> > > Some ideas:
> > > 1) add new functions to the canvas 2D context, such as:
> > > ctx.load(image): cache an image in memory so it can be immediately
> drawn
> > > when drawImage() is first used
> > > ctx.unload(image): release the image from memory
> >
> > The Web API tries to use garbage collection for this; the idea being that
> > you load the images you need when you need them, then discard then when
> > you're done, and the memory gets reclaimed when possible.
> >
> > We could introduce a mechanism to flush ImageBitmap objects more
> forcibly,
> > e.g. imageBitmap.discard(). This would be a pretty new thing, though. Are
> > there any browser vendors who have opinions about this?
> >
> > We should probably wait to see if people are able to use ImageBitmap with
> > garbage collection first. Note, though, that ImageBitmap doesn't really
> > add anything you couldn't do with <img> before, in the non-Worker case.
> > That is, you could just create <img> elements then lose references to
> them
> > when you wanted them GC'ed; if that isn't working today, I don't see why
> > it would start working with ImageBitmap.
> >
> > --
> > Ian Hickson               U+1047E                )\._.,--....,'``.    fL
> > http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
> > Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
> >
>