Fix cursor appearing on rerender when at bottom

When sitting at the bottom of a room with cursor = Cursor::Bottom, a
rerender would make the cursor jump to the lowest visible message. This
of course should only happen when the screen is scrolled, not on almost
every rerender.

src/ui/chat/tree.rs

@@ -24,6 +24,11 @@ use super::ChatMsg;
 // State //
 ///////////
 
+enum Correction {
+    MakeCursorVisible,
+    MoveCursorToVisibleArea,
+}
+
 struct InnerTreeViewState<M: Msg, S: MsgStore<M>> {
     store: S,
 
@@ -31,14 +36,11 @@ struct InnerTreeViewState<M: Msg, S: MsgStore<M>> {
     last_cursor_line: i32,
 
     cursor: Cursor<M::Id>,
-    /// Set to true if the chat should be scrolled such that the cursor is fully
-    /// visible (if possible). If set to false, then the cursor itself is moved
-    /// to a different message such that it remains visible.
-    make_cursor_visible: bool,
 
     /// Scroll the view on the next render. Positive values scroll up and
     /// negative values scroll down.
     scroll: i32,
+    correction: Option<Correction>,
 
     editor: EditorState,
 }
@@ -50,8 +52,8 @@ impl<M: Msg, S: MsgStore<M>> InnerTreeViewState<M, S> {
             last_cursor: Cursor::Bottom,
             last_cursor_line: 0,
             cursor: Cursor::Bottom,
-            make_cursor_visible: false,
             scroll: 0,
+            correction: None,
             editor: EditorState::new(),
         }
     }

src/ui/chat/tree/cursor.rs

@@ -2,7 +2,7 @@
 
 use crate::store::{Msg, MsgStore, Tree};
 
-use super::InnerTreeViewState;
+use super::{Correction, InnerTreeViewState};
 
 #[derive(Debug, Clone, Copy)]
 pub enum Cursor<I> {
@@ -177,7 +177,7 @@ impl<M: Msg, S: MsgStore<M>> InnerTreeViewState<M, S> {
                 self.cursor = Cursor::Msg(id);
             }
         }
-        self.make_cursor_visible = true;
+        self.correction = Some(Correction::MakeCursorVisible);
     }
 
     pub async fn move_cursor_down(&mut self) {
@@ -208,28 +208,30 @@ impl<M: Msg, S: MsgStore<M>> InnerTreeViewState<M, S> {
             }
             _ => {}
         }
-        self.make_cursor_visible = true;
+        self.correction = Some(Correction::MakeCursorVisible);
     }
 
     pub async fn move_cursor_to_top(&mut self) {
         if let Some(first_tree_id) = self.store.first_tree_id().await {
             self.cursor = Cursor::Msg(first_tree_id);
-            self.make_cursor_visible = true;
+            self.correction = Some(Correction::MakeCursorVisible);
         }
     }
 
     pub async fn move_cursor_to_bottom(&mut self) {
         self.cursor = Cursor::Bottom;
         // Not really necessary; only here for consistency with other methods
-        self.make_cursor_visible = true;
+        self.correction = Some(Correction::MakeCursorVisible);
     }
 
     pub fn scroll_up(&mut self, amount: i32) {
         self.scroll += amount;
+        self.correction = Some(Correction::MoveCursorToVisibleArea);
     }
 
     pub fn scroll_down(&mut self, amount: i32) {
         self.scroll -= amount;
+        self.correction = Some(Correction::MoveCursorToVisibleArea);
     }
 }
 

src/ui/chat/tree/layout.rs

@@ -7,7 +7,7 @@ use crate::ui::widgets::text::Text;
 use crate::ui::ChatMsg;
 
 use super::tree_blocks::{BlockId, Root, TreeBlocks};
-use super::{widgets, Cursor, InnerTreeViewState};
+use super::{widgets, Correction, Cursor, InnerTreeViewState};
 
 impl<M: Msg + ChatMsg, S: MsgStore<M>> InnerTreeViewState<M, S> {
     async fn cursor_path(&self, cursor: &Cursor<M::Id>) -> Path<M::Id> {
@@ -410,11 +410,13 @@ impl<M: Msg + ChatMsg, S: MsgStore<M>> InnerTreeViewState<M, S> {
                 .await;
         }
 
-        if self.make_cursor_visible {
+        match self.correction {
+            Some(Correction::MakeCursorVisible) => {
                 self.scroll_so_cursor_is_visible(frame, &mut blocks);
                 self.fill_screen_and_clamp_scrolling(frame, &mut blocks)
                     .await;
-        } else {
+            }
+            Some(Correction::MoveCursorToVisibleArea) => {
                 let new_cursor_msg_id = self.move_cursor_so_it_is_visible(frame, &blocks);
                 if let Some(cursor_msg_id) = new_cursor_msg_id {
                     // Moving the cursor invalidates our current blocks, so we sadly
@@ -423,8 +425,8 @@ impl<M: Msg + ChatMsg, S: MsgStore<M>> InnerTreeViewState<M, S> {
 
                     self.last_cursor = self.cursor.clone();
                     self.last_cursor_line = self.cursor_line(&blocks);
-                self.make_cursor_visible = false;
                     self.scroll = 0;
+                    self.correction = None;
 
                     let last_cursor_path = self.store.path(&cursor_msg_id).await;
                     blocks = self.layout_last_cursor_seed(frame, &last_cursor_path).await;
@@ -432,11 +434,13 @@ impl<M: Msg + ChatMsg, S: MsgStore<M>> InnerTreeViewState<M, S> {
                         .await;
                 }
             }
+            None => {}
+        }
 
         self.last_cursor = self.cursor.clone();
         self.last_cursor_line = self.cursor_line(&blocks);
-        self.make_cursor_visible = false;
         self.scroll = 0;
+        self.correction = None;
 
         blocks
     }