documents and editor: a writing view - measure, font, scale, focus fading, typewriter centering

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/documents/document/look.rs

@@ -0,0 +1,80 @@
+//! A writing view: how text shows, not what it says.
+
+use gpui::{Context, Rems, SharedString};
+
+use super::MarkdownDocument;
+use crate::documents::MarkdownMode;
+
+/// How the document shows its text (MARK-09).
+#[derive(Clone, Debug, PartialEq)]
+pub struct DocumentLook {
+    /// All but the current block or line fade.
+    pub focus: bool,
+    /// The current block or line stays mid-view.
+    pub typewriter: bool,
+    /// The widest the text column grows.
+    pub measure: Option<Rems>,
+    /// The prose font; none keeps the theme's.
+    pub font: Option<SharedString>,
+    /// Text size against the theme's.
+    pub scale: f32,
+}
+
+impl Default for DocumentLook {
+    fn default() -> Self {
+        Self {
+            focus: false,
+            typewriter: false,
+            measure: None,
+            font: None,
+            scale: 1.0,
+        }
+    }
+}
+
+impl MarkdownDocument {
+    pub fn look(&self) -> &DocumentLook {
+        &self.look
+    }
+
+    pub fn set_look(&mut self, look: DocumentLook, cx: &mut Context<Self>) {
+        log::info!("markdown document: look {look:?}");
+        self.editor.update(cx, |editor, cx| {
+            editor.set_scale(look.scale, cx);
+            editor.set_focus_line(look.focus, cx);
+            editor.set_typewriter(look.typewriter, cx);
+        });
+        self.look = look;
+        self.centered = None;
+        cx.notify();
+    }
+
+    /// The reader's block: the open one, or the caret's.
+    pub(super) fn current_block(&self, cx: &gpui::App) -> usize {
+        match &self.open {
+            Some(open) if open.append => self.parsed.blocks.len(),
+            Some(open) => self.block_at(open.range.start),
+            None => self.block_at(self.editor.read(cx).primary().head),
+        }
+    }
+
+    /// The current block mid-view once it or its text moves.
+    pub(super) fn center_current(&mut self, cx: &gpui::App) {
+        if !self.look.typewriter || self.mode != MarkdownMode::Visual {
+            return;
+        }
+        let ix = self.current_block(cx);
+        let Some(block) = self.list.bounds_for_item(ix) else {
+            return;
+        };
+        // A new layout moves it too: its height counts.
+        let height = f32::from(block.size.height).round() as u64;
+        let moved = (ix, self.edits, self.typed, height);
+        if self.centered == Some(moved) {
+            return;
+        }
+        let view = self.list.viewport_bounds();
+        self.list.scroll_by(block.center().y - view.center().y);
+        self.centered = Some(moved);
+    }
+}