Bug 310346 – REGRESSION(308458@main): [GTK][WPE] dirty scrollbar thumb

• Component: WebKitGTK
• Status: RESOLVED DUPLICATE

[Fujii Hironori]

1. Load your random favorite web site
2. Hover the mouse cursor on the vertical scrollbar to make it wider
3. Send wheel event to scroll the page

The scrollbar thumb sometime looks dirty.

I realized this problem with GTK MiniBrowser 309519@main Release build and Epiphany Canary of today.
I don't know the exact steps to reproduce. But, very easy to reproduce by visiting some favorite web sites.

https://en.wikipedia.org/wiki/Main_Page
https://www.yomiuri.co.jp/
https://www.itmedia.co.jp/
https://news.yahoo.co.jp/

[Fujii Hironori]

Created attachment 478729 [details]
screenshot

[Fujii Hironori]

bisecting...

308516@main bad
308440@main good

https://commits.webkit.org/compare/308440@main...308516@main

[Fujii Hironori]

308458@main is the regression point.

[Fujii Hironori]

No wheel events are needs. No needs to scroll. 

1. Load a random page in https://en.wikipedia.org/
2. Hover the mouse cursor to make the overlay scrollbar wider
3. Look at the scrollbar 

I see the problem just by repeating these steps 2-3 times.

[Fujii Hironori]

This patch fills the scrollbar area with semi-transparent white.
With this patch, easier to observe the dirty scrollbar area.

diff --git a/Source/WebCore/platform/adwaita/AdwaitaScrollbarPainter.cpp b/Source/WebCore/platform/adwaita/AdwaitaScrollbarPainter.cpp
index fb108ceaaf42..456273811aeb 100644
--- a/Source/WebCore/platform/adwaita/AdwaitaScrollbarPainter.cpp
+++ b/Source/WebCore/platform/adwaita/AdwaitaScrollbarPainter.cpp
@@ -34,6 +34,10 @@ namespace WebCore::AdwaitaScrollbarPainter {
 
 void paint(GraphicsContext& graphicsContext, const IntRect& damageRect, const State& scrollbar)
 {
+    graphicsContext.beginTransparencyLayer(0.5);
+    graphicsContext.fillRect(scrollbar.frameRect, Color::white);
+    graphicsContext.endTransparencyLayer();
+    return;
     if (graphicsContext.paintingDisabled())
         return;

[Fujii Hironori]

If I replace beginTransparencyLayer with Color(Color::blue).colorWithAlpha(0.5), this issue no longer happen.

[Fujii Hironori]

*** This bug has been marked as a duplicate of bug 311086 ***