[Webkit-unassigned] [Bug 175138] New: Replacing the src attribute via JavaScript results in flickering

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=175138

            Bug ID: 175138
           Summary: Replacing the src attribute via JavaScript results in
                    flickering
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: iPhone / iPad
                OS: iOS 11
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: frank at raureif.net
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 317127

  --> https://bugs.webkit.org/attachment.cgi?id=317127&action=review

A screencast that shows image flickering in Safari on iOS 11 b4.

Replacing the `src` attribute of an `<img>` via JavaScript results in flickering.

HTML/JS demo here: 
http://temp.frankrausch.com/webkit-image-flicker/


# Steps to Reproduce:

1) Replace an image with another image by changing the `src` attribute of an `<img>` via JavaScript.

    For example: 
    image.setAttribute("src", "bastille-large.jpg");


# Actual Results:

The old image is visually removed for a split second, resulting in flickering.
This only seems to happen when loading an image that has not been displayed before.


# Expected Results:

The new image should appear instantly as soon as it’s been downloaded, without the old image disappearing. This was the case in iOS <=10.


# Software Version:

This occurs on iOS 11 beta 4; in Safari and also in my app’s WKWebView.


# Additional Information:

I use this library to lazy-load high-resolution versions of images in my app. 
https://github.com/verlok/lazyload
It shows the low-resolution images in `src` by default and lazy-loads the high-resolution versions from a `data-src` attribute.

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