[Webkit-unassigned] [Bug 153405] [GTK] Implement overlay scrollbars

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=153405

--- Comment #8 from Carlos Garcia Campos <cgarcia at igalia.com> ---
(In reply to comment #4)
> Comment on attachment 269692 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=269692&action=review
> 
> > Source/WebCore/platform/gtk/ScrollbarThemeGtk.cpp:238
> > +    m_usesOverlayScrollbars = g_strcmp0(g_getenv("GTK_OVERLAY_SCROLLING"), "0");
> 
> Is this really the right test...?

Yes.

> It's not a style property?

No. It's GtkScrolledWindow API, gtk_scrolled_window_set_overlay_scrolling(). We could probably add a WebKitSetting.

> I assumed this
> variable was to turn off overlay scrolling for debugging purposes.

Yes, this is probably just for debugging, I'm not sure it's documented. I added it to match what GTK does, so that if someone runs any GTK+ app containing a WebView with the env var, we will honor it too. And also made my life easier when developing this. 

> Are all
> themes expected to implement overlay scrollbars?

It doesn't really matter. If a theme doesn't implement overlay scrollbars, the overlay-indicator class will not have any effect in the rendering, so we will end up rendering the scrollbars following the theme but on top of the contents and hiding/showing them. Same would happen with GtkScrolledWindow, and I would say it's a theme issue not ours.

> I'm halfway pleased that the technical limitation of threaded compositor
> necessitates implementing overlay scrollbars, because now we have overlay
> scrollbars. But it's disappointing that threaded compositor will prevent us
> from rendering non-overlay scrollbars. I expect this could cause scrollbars
> to look quite bad with anything besides Adwaita or Ambiance. Can you or Yoon
> explain the technical limitation here?

I have no idea. But I don't think it's that problematic, GTK+ is unusable with any other theme than Adwaita nowadays, and new themes will probably implement olverlay-indicator to look good with GtkScrolledwindow.

> > Source/WebCore/platform/gtk/ScrollbarThemeGtk.cpp:432
> > +#if GTK_CHECK_VERSION(3, 19, 8)
> 
> I don't understand this version check. 3.19.7 was released last week; I
> don't see any scrollbar-related changes since then?

https://git.gnome.org/browse/gtk+/commit/?id=0f7b4dad0f6cef80172638efb019ce094d7eadee

> I would just get rid of the check; it's enough that the code works with GTK+
> master, that's what you and I are going to use, we're the people testing it
> so optimize for us. Otherwise I'd have to manually remove the check to test
> this code.

It will probably crash if someone uses 3.19.7, it's just temporary, we should change all the ifdefs in this file (and RenderThemeGtk) once 3.20 is released.

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