Re: [Flightgear-devel] Make Canvas windows reusable by not destroying them on closing

[James T. <ja...@fl...>]

> On 10 Oct 2022, at 15:17, TheFGFSEagle <the...@gm...> wrote:
> 
> As for memory usage, I did a test - 100 1000x1000 px canvas windows, all with destroy_on_close = 0. constructing them didn't give a significant increase in memory usage - only upon showing them all at once, the RAM usage went up by 2 GB. that's quite a lot you might say, but 1) most dialogs are not as big as that and 2) which user opens 100 dialogs in one session ? In most cases it won't be more than 10 = 200 MB RAM (if all dialogs were using this new behaviour) - and the default behaviour is to destroy the window on closing anyways (destroy_on_close = 1 by default, you got to explicitly set it to 0 to get the new behaviour, also to maintain backwards compatibility), so I think this won't be an issue.

What we’d ideally want is a C++ change so that hidden canvases release their texture memory : it’s created the first time the canvas is rendered, which is why the memory is fine until you actually show them.

200MB memory is not great, but the bigger problem is the GPU-side memory : 200MB of VRAM is much more ‘valuable’ for textures than for keeping the backing store of hidden dialogs. So I would definitely say use this feature sparingly, until someone adds some C++ logic to destroy the backing texture for hidden canvas windows.

Kind regards,
James