T16 round 2 fixes: synced charts move their shared window once per append, Fibonacci labels sit in a box clipped to the price pane and flip below near its top, and prices show every place their tick needs

src/finance/labels.rs

@@ -1,6 +1,9 @@
 use std::ops::Range;
 
-use gpui::{App, Div, FontWeight, Hsla, ParentElement, Pixels, SharedString, Styled, Window, div};
+use gpui::{
+    App, Div, FontWeight, Hsla, ParentElement, Pixels, SharedString, Styled, Window, div,
+    prelude::*,
+};
 use jiff::tz::TimeZone;
 
 use super::{
@@ -12,7 +15,7 @@ use super::{
 use crate::{
     charts::{Linear, Rect, tint},
     theme::{ActiveTheme, Radius, TextSize},
-    typography::{format, tabular},
+    typography::{LEADING, format, tabular},
 };
 
 /// Where a market chart's words go: its panes and their scales, what is in view, the candle and row under the pointer, the zone its times read in, its title, and a compared symbol's name.
@@ -220,6 +223,8 @@ pub(crate) fn labels(
             })));
         }
     }
+    let tall = f32::from(small.to_pixels(rem)) * LEADING;
+    let mut levels = Vec::new();
     for drawing in &axes.drawings {
         let Drawing::Fib(from, to) = *drawing else {
             continue;
@@ -228,30 +233,48 @@ pub(crate) fn labels(
         if x > main.x + main.w {
             continue;
         }
-        let x = x.max(main.x);
-        let inside = |y: f32| y >= main.y && y <= main.y + main.h;
-        for (share, value) in Drawing::levels(from, to)
-            .into_iter()
-            .filter(|(_, value)| inside(price.at(*value)))
-        {
+        let left = (x - main.x).max(0.0);
+        for (share, value) in Drawing::levels(from, to) {
+            let y = price.at(value) - main.y;
+            if !(0.0..=main.h).contains(&y) {
+                continue;
+            }
             let words = format!(
                 "{} {}",
                 format::percent(share, 1, false),
                 format::number(value, digits, format::Separators::EN)
             );
-            out.push(
+            let above = y >= tall;
+            levels.push(
                 div()
                     .absolute()
-                    .left(Pixels::from(x))
-                    .top(Pixels::from(price.at(value)))
+                    .left(Pixels::from(left))
+                    .top(Pixels::from(y))
                     .h_0()
                     .flex()
-                    .items_end()
                     .pl_1()
-                    .child(tabular(text(words, colors.fg_muted)).pb_0p5()),
+                    .when(above, |label| label.items_end())
+                    .when(!above, |label| label.items_start())
+                    .child(
+                        tabular(text(words, colors.fg_muted))
+                            .when(above, |words| words.pb_0p5())
+                            .when(!above, |words| words.pt_0p5()),
+                    ),
             );
         }
     }
+    if !levels.is_empty() {
+        out.push(
+            div()
+                .absolute()
+                .left(Pixels::from(main.x))
+                .top(Pixels::from(main.y))
+                .w(Pixels::from(main.w))
+                .h(Pixels::from(main.h))
+                .overflow_hidden()
+                .children(levels),
+        );
+    }
     let pill = |y: f32, words: String, (fill, ink): (Hsla, Hsla)| {
         let body = tabular(div())
             .px_1p5()

src/finance/market.rs

@@ -40,6 +40,8 @@ pub enum ChartKind {
 pub struct ChartSync {
     pub(crate) visible: Option<Visible>,
     pub(crate) hover: Option<i64>,
+    /// How many candles the shared window last moved for, so one append moves it once.
+    pub(crate) seen: usize,
 }
 
 /// A market's prices over time as candles, bars or a line, on a price scale at the right. Drag or scroll sideways to move through time, hold Cmd and scroll to zoom, and double-press to return to the newest; the crosshair reads each candle.
@@ -232,7 +234,10 @@ impl RenderOnce for CandlestickChart {
             Some(sync) => (sync.read(cx).visible, sync.read(cx).hover),
             None => (stage.read(cx).visible, stage.read(cx).hover),
         };
-        let seen = stage.read(cx).seen;
+        let seen = match &self.sync {
+            Some(sync) => sync.read(cx).seen,
+            None => stage.read(cx).seen,
+        };
         let visible = match held.0 {
             Some(visible)
                 if total > seen
@@ -246,12 +251,16 @@ impl RenderOnce for CandlestickChart {
         };
         if seen != total {
             log::debug!("market chart: {seen} candles to {total}");
-            stage.update(cx, |stage, _| stage.seen = total);
-            if held.0.is_some() {
-                match &self.sync {
-                    Some(sync) => sync.update(cx, |sync, _| sync.visible = Some(visible)),
-                    None => stage.update(cx, |stage, _| stage.visible = Some(visible)),
-                }
+            let kept = held.0.map(|_| visible);
+            match &self.sync {
+                Some(sync) => sync.update(cx, |sync, _| {
+                    sync.seen = total;
+                    sync.visible = kept.or(sync.visible);
+                }),
+                None => stage.update(cx, |stage, _| {
+                    stage.seen = total;
+                    stage.visible = kept.or(stage.visible);
+                }),
             }
         }
         let range = visible.range(total);

src/finance/mod.rs

@@ -22,6 +22,8 @@ mod stage;
 mod steer;
 mod symbols;
 mod tape;
+#[cfg(all(test, feature = "test-support"))]
+mod tests;
 mod tools;
 mod trade;
 mod wallet;

src/finance/stage.rs

@@ -104,12 +104,15 @@ pub(crate) fn fit(low: f64, high: f64) -> ((f64, f64), Vec<f64>) {
     ((low, high), inside)
 }
 
-/// Places after the point that ticks `step` apart need: none for whole steps, two for cents.
+/// Places after the point that show every multiple of `step` exactly: none for whole steps, four for 0.0025.
 pub(crate) fn decimals(step: f64) -> usize {
-    if step >= 1.0 || step <= 0.0 {
-        return 0;
-    }
-    (-step.log10() - 1e-9).ceil().max(0.0) as usize
+    assert!(
+        step.is_finite() && step > 0.0,
+        "a step is positive, not {step}"
+    );
+    let text = format!("{step:.10}");
+    let fraction = text.split_once('.').map_or("", |(_, fraction)| fraction);
+    fraction.trim_end_matches('0').len()
 }
 
 #[cfg(test)]
@@ -198,5 +201,11 @@ mod tests {
             ),
             (0, 1, 2, 3)
         );
+        assert_eq!(decimals(0.0025), 4, "a quarter of a cent needs four places");
+        assert_eq!(
+            decimals(110.2 - 110.0),
+            1,
+            "float noise from a difference drops away"
+        );
     }
 }

src/finance/tests.rs

@@ -0,0 +1,66 @@
+use std::rc::Rc;
+
+use gpui::{
+    AppContext as _, Context, Entity, IntoElement, ParentElement, Render, Styled, TestAppContext,
+    Window, div, px,
+};
+use jiff::Timestamp;
+
+use crate::finance::{CandlestickChart, ChartSync, candles::Candle, stage::Visible};
+use crate::theme::Theme;
+
+fn candles(count: usize) -> Rc<Vec<Candle>> {
+    Rc::new(
+        (0..count)
+            .map(|ix| {
+                let time = Timestamp::from_second(ix as i64 * 86_400).expect("a day");
+                Candle::new(time, (10.0, 11.0, 9.0, 10.0 + ix as f64 * 0.01), 100.0)
+            })
+            .collect(),
+    )
+}
+
+struct Pair {
+    candles: Rc<Vec<Candle>>,
+    sync: Entity<ChartSync>,
+}
+
+impl Render for Pair {
+    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
+        div()
+            .w(px(800.))
+            .child(CandlestickChart::new("first", self.candles.clone()).sync(&self.sync))
+            .child(CandlestickChart::new("second", self.candles.clone()).sync(&self.sync))
+    }
+}
+
+#[gpui::test]
+fn synced_charts_move_their_shared_window_once_per_append(cx: &mut TestAppContext) {
+    cx.update(Theme::init);
+    let sync = cx.new(|_| ChartSync::default());
+    let shared = sync.clone();
+    let (view, cx) = cx.add_window_view(|_, _| Pair {
+        candles: candles(40),
+        sync: shared,
+    });
+    cx.run_until_parked();
+    sync.update(cx, |sync, cx| {
+        sync.visible = Some(Visible {
+            start: 20.0,
+            count: 20.0,
+        });
+        cx.notify();
+    });
+    view.update(cx, |_, cx| cx.notify());
+    cx.run_until_parked();
+    view.update(cx, |pair, cx| {
+        pair.candles = candles(45);
+        cx.notify();
+    });
+    cx.run_until_parked();
+    let start = sync.read_with(cx, |sync, _| sync.visible.expect("held").start);
+    assert_eq!(
+        start, 25.0,
+        "five new candles move the shared window five, not ten"
+    );
+}