On my laptop (4k screen so hidpi scaling is probably relevant), just starting the browser on about:newtab makes us (re)allocate the 512x512 color texture array 5 times, with 2, 6 ,7 ,8 and finally 9 layers before the page stabilizes. After that going to https://fr.wikipedia.org/wiki/Caf%C3%A9 causes us to reallocate the texture array with 10, 11, 15, 16 and 18 layers before the page stabilizes. After leaving the tab idle for a moment, it looks like the array is resized down to 12 layers. Then, scrolling that page all the way to the bottom makes us reallocate the texture array a bunch, until we reach 27 layers. I think that it is safe to assume that we can start with a larger texture array for main windows (the layer count won't go below 10 on simple web pages on my laptop), and grow it at a coarser granularity. This would be a nice occasion to pick a larger size for the array layers (maybe 1024x0124), allowing slightly larger images to participate in batching. Maybe start with 4 1024x1024 layers for the main window and keep small 512x512 arrays for popups initially.
Bug 1616901 Comment 1 Edit History
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On my laptop (4k screen so hidpi scaling is probably relevant), just starting the browser on about:newtab makes us (re)allocate the 512x512 color texture array 5 times, with 2, 6 ,7 ,8 and finally 9 layers before the page stabilizes. After that going to https://fr.wikipedia.org/wiki/Caf%C3%A9 causes us to reallocate the texture array with 10, 11, 15, 16 and 18 layers before the page stabilizes. After leaving the tab idle for a moment, it looks like the array is resized down to 12 layers. Then, scrolling that page all the way to the bottom makes us reallocate the texture array a bunch, until we reach 27 layers. I think that it is safe to assume that we can start with a larger texture array for main windows (the layer count won't go below 10 on simple web pages on my laptop), and grow it at a coarser granularity. This would be a nice occasion to pick a larger size for the array layers (maybe 1024x0124), allowing slightly larger images to participate in batching. Maybe start with 4 1024x1024 layers for the main window and keep small 512x512 arrays for popups initially. Edit: I got the same results running the steps above with a device pixel ratio of 1 at a quarter of the screen resolution.