[Webkit-unassigned] [Bug 175423] New: Scroll performance is impacted when having a fixed background followed by other backgrounds.

Thu Aug 10 03:18:59 PDT 2017

https://bugs.webkit.org/show_bug.cgi?id=175423

            Bug ID: 175423
           Summary: Scroll performance is impacted when having a fixed
                    background followed by other backgrounds.
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: futursolo at icloud.com

The frame rate of the following page drops significantly when scrolling.

> <html>
>   <head>
>     <style>
>     body {
>       background: url(background.jpg) fixed, #eee;
>       height: 10000px;  /* to make the page scrollable. */
>     }
>     .boxes {
>       border: 1px solid #000;
>       height: 200px;
>       width: 200px;
>       filter: drop-shadow(0 50px 50px #ddd);
>     }
>     </style>
>   </head>
>   <body>
>     <div class="boxes"></div>
>     <div class="boxes"></div>
>     <div class="boxes"></div>
>   </body>
> </html>

Two possible workarounds are either remove the filter from the boxes class or remove the second background from the body.

The web inspector shows that it takes WebKit a long time on compositing and painting.

The same page tested under Firefox 56.0b1 rendered with no problem when scrolling.

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