[Webkit-unassigned] [Bug 187374] New: [iOS] When asking for FlushImmediately, the UIProcess should ignore all the layer tree transactions which are sent before this request is received by the WebProcess

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=187374

            Bug ID: 187374
           Summary: [iOS] When asking for FlushImmediately, the UIProcess
                    should ignore all the layer tree transactions which
                    are sent before this request is received by the
                    WebProcess
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Images
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: sabouhallawa at apple.com

When Mobile Safari is brought to the foreground, it may have a snapshot from the page before it went to sleep. An immediate update is needed to refresh the page in case the contents have changed. In this case, we need to draw all the images synchronously even if the tile is painted for the first time. This will prevent unwanted flashing in case the page contents were not changed.

To do that:

-- SetActivityState message will include an activityStateChangeID member.

-- LayerTreeTransaction will include an activityStateChangeID member.

-- UIProcess sends an activityStateChangeID with the SetActivityState message if FlushImmediately paint is needed. Otherwise it sends zero. UIProcess waits for the LayerTreeTransaction whose activityStateChangeID is greater than or equal to the one it sent. If it receives the desired LayerTreeTransaction, the tree layer will be committed otherwise it will be ignored.

-- WebProcess will read the activityStateChangeID from the SetActivityState message and will pass it in LayerTreeTransaction. Otherwise it will pass zero.

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