mirror of https://github.com/zulip/zulip.git
116 lines
5.0 KiB
Markdown
116 lines
5.0 KiB
Markdown
# Unread counts and the pointer
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When you're using Zulip and you reload, or narrow to a stream, how
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does Zulip decide where to place you?
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Conceptually, Zulip takes you to the place where you left off
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(e.g. the first unread message), not the most recent messages, to
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facilitate reviewing all the discussions that happened while you were
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away from your computer. The scroll position is then set to keep that
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message in view and away from both the top and bottom of the visible
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section of messages.
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But there a lot of details around doing this right, and around
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counting unread messages. Here's how Zulip currently decides which
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message to select, along with some notes on improvements we'd like to
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make to the model.
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First a bit of terminology:
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* "Narrowing" is the process of filtering to a particular subset of
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the messages the user has access to.
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* The blue cursor box (the "pointer") is around is called the
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"selected" message. Zulip ensures that the currently selected
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message is always in-view.
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## Pointer logic
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### Recipient bar: message you clicked
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If you enter a narrow by clicking on a message group's *recipient bar*
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(stream/topic or private message recipient list at the top of a group
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of messages), Zulip will select the message you clicked on. This
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provides a nice user experience where you get to see the stuff near
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what you clicked on, and in fact the message you clicked on stays at
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exactly the same scroll position in the window after the narrowing as
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it was at before.
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### Search, sidebar click, or new narrowed tab: unread/recent matching narrow
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If you instead narrow by clicking on something in the left sidebar or
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typing some terms into the search box, Zulip will instead select
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the first unread message matching that narrow, or if there are none,
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the most recent messages matching that narrow. This provides the nice
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user experience of taking you to the start of the new stuff (with
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enough messages you'ev seen before still in view at the top to provide
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you with context), which is usually what you want. (When finding the
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"first unread message", Zulip ignores unread messages in muted streams
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or in muted topics within non-muted streams.)
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### Unnarrow: previous sequence
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When you unnarrow using e.g. the escape key, you will automatically be
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taken to the same message that was selected in the All messages view before
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you narrowed, unless in the narrow you read new messages, in which
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case you will be jumped forward to the first unread and non-muted
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message in the All messages view (or the bottom of the feed if there is
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none). This makes for a nice experience reading threads via the All messages
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view in sequence.
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### New All messages view: "high watermark"
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When you open a new browser window or tab to the All messages view (a.k.a. the
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interleaved view you get if you visit `/`), Zulip will select the
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furthest down that your cursor has ever reached in the All messages
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view. Because of the logic around unnarrowing in the last bullet, this
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is usually just before the first unread message in the All messages view, but
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if you never go to the All messages view, or you leave messages unread on some
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streams in your All messages view, this can lag.
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We plan to change this to automatically advance the pointer in a way
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similar to the unnarrow logic.
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### Forced reload: state preservation
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When the server forces a reload of a browser that's otherwise caught
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up (which happens within 30 minutes when a new version of the server
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is deployed, usually at a type when the user isn't looking at the
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browser), Zulip will preserve the state -- what (if any) narrow the
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user was in, the selected message, and even exact scroll position!
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For more on the user experience philosophy guiding these decisions,
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see [the architectural overview](../overview/architecture-overview.md).
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## Unread count logic
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How does Zulip decide whether a message has been read by the user?
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The algorithm needs to correctly handle a range of ways people might
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use the product. The algorithm is as follows:
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* Any message which is selected or above a message which is selected
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is marked as read. So messages are marked as read as you scroll
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down the keyboard when the pointer passes over them.
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* If the whitespace at the very bottom of the feed is in view, all
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messages in view are marked as read.
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These two simple rules, combined with the pointer logic above, end up
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matching user expectations well for whether the product should treat
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them as having read a set of messages (or not).
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One key detail to highlight is that we only mark messages as read
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through these processes in views that contain all messages in a
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thread; search views will never mark messages as read.
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## Testing and development
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In a Zulip development environment, you can use `manage.py
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mark_all_messages_unread` to set every user's pointer to 0 and all
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messages as unread, for convenience in testing unread count related
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logic.
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It can be useful to combine this with `manage.py populate_db -n 3000`
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(which rebuilds the database with 3000 initial messages) to ensure a
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large number of messages are present.
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