[Webkit-unassigned] [Bug 204552] [GTK] Catastrophic VSYNC failure

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=204552

--- Comment #5 from Miguel Gomez <magomez at igalia.com> ---
I've been giving this a look. There are several things that are happening here:

- The page does a lot of canvas rendering to stress the browser and check whether it's able to keep up with the display frequency. The default behavior, while works fine on chrome and firefox, is too heavy for wkgtk (or wpe). The canvas rendering operations take too long to achieve 60fps. It gets much better disabling the background images option, which disables the canvas rendering. But..

- The page doesn't trigger AC mode. In this situation, there seems to be a problem detecting the display frequency and the framerate gets stuck at ~26fps. But using the Custom framerate option and setting it to 60 works fine. There must be some problem detecting the display frequency in non AC mode.

- If AC mode is forced (with WEBKIT_FORCE_COMPOSITING_MODE=1) and disabling the background images, the display frequency is detected as ~56Hz and the framerate follows that value. Using a custom value works fine as well.

So, two things to look into:
- why the low performance on the canvas paintings in comparison with chrome and firefox (the execution of the rAF callback takes ~45ms, which is a lot, it should be under 16ms to get to 60fps)
- why the display frequency is not properly detected when in AC mode

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