Green read-marker unexpected behaviour in rooms with many unread messages

[benparsons]

Description

Previously, in a room with many unread messages, the green bar would "follow" you as you scroll down the page. This no longer seems to happen, although the behaviour is the same.

Steps to reproduce

• Enter a room with many unread messages
• Click to go to the first unread message
• scroll down
• green marker doesn't follow

Version information

• Platform: web

For the web app:

• Browser: Firefox 69
• OS: macOS
• URL: riot.im/develop

[MadLittleMods]

Read-marker (Unread horizon) keeps showing messages as unread as I scroll down.

In a room with a bunch of unread messages, I click the arrow to jump up to the first unread to scroll down but then the arrow shows again and if I scroll up, the read-marker is just above my scroll where I already was.

It appears that the messages aren’t getting marked as read. When I go back to the room, the unread arrow dumps me back to where I’ve already read.

This comment seems to explain it well:

It seems that there is currently a "few hundred ms" delay while reading, which is way too slow and means that scrolling through the unread messages will leave some of them marked unread.

-- #1681 (comment)

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• Platform: web
• Browser: Chrome 91.0.4472.101
• OS: Windows 10
• URL: Any room with lots of unreads

[turt2live]

I think this needs design in order to consider what the feature is supposed to do, which might require spiking a small effort to make it consistent with that design outcome. At the moment we just don't have the requirements for the system written down (to my knowledge - happy to be proven wrong. Encouraged to prove me wrong, even).