Decrease Font Size steps down one size at a time from any size (#2070)

Ctrl+[ (and Cmd+Shift+,) shrank any size above 66 straight to 66: the
step list stopped at 66, so the largest list size below 120 was 66.
The list now holds PowerPoint's sizes up to 96, as the Font Size box
already listed them, and above 96 shrink steps back 8 points at a
time, as grow steps up: 120 -> 112 -> 104 -> 96 -> 88 -> 80 -> 72 ->
66. The Font Size box lists the same SIZES instead of adding its own
tail.

Fixes #2059

crates/engine/src/cmd/format/font.rs

@@ -55,12 +55,18 @@ pub(super) fn size(s: &mut Session, p: &Value) -> Result<Value> {
     format_run(s, &move |r| r.size = Some(v))
 }
 
-/// PowerPoint's font size list (grow/shrink steps through it).
-pub const SIZES: [f64; 20] = [8.0, 9.0, 10.0, 10.5, 11.0, 12.0, 14.0, 16.0, 18.0, 20.0, 24.0, 28.0, 32.0, 36.0, 40.0, 44.0, 48.0, 54.0, 60.0, 66.0];
+/// PowerPoint's font size list, as the Font Size box lists it (grow/shrink steps through it).
+pub const SIZES: [f64; 24] =
+    [8.0, 9.0, 10.0, 10.5, 11.0, 12.0, 14.0, 16.0, 18.0, 20.0, 24.0, 28.0, 32.0, 36.0, 40.0, 44.0, 48.0, 54.0, 60.0, 66.0, 72.0, 80.0, 88.0, 96.0];
 
+/// Grow steps up the list, then 8 points at a time past its top; shrink steps back down the same
+/// way. A size past the top used to shrink straight to 66 (#2059).
 fn step(cur: f64, up: bool) -> f64 {
+    let top = SIZES[SIZES.len() - 1];
     if up {
         SIZES.iter().copied().find(|v| *v > cur + 0.01).unwrap_or((cur + 8.0).min(4000.0))
+    } else if cur - 0.01 > top {
+        (cur - 8.0).max(top)
     } else {
         SIZES.iter().rev().copied().find(|v| *v < cur - 0.01).unwrap_or((cur - 1.0).max(1.0))
     }

crates/engine/src/tests.rs

@@ -6921,6 +6921,37 @@ fn master_body_placeholder_format_keeps_per_level_formatting() {
     assert_eq!(shown(&s), vec![Some(28.0), Some(24.0)]);
 }
 
+/// #2059: Decrease Font Size (Ctrl+[, Cmd+Shift+,) steps down one size at a time from any size:
+/// PowerPoint's list up to 96, then 8 points at a time above it, as Increase Font Size steps up.
+/// A size above 66 used to shrink straight to 66.
+#[test]
+fn shrinking_a_large_font_steps_down_one_size_at_a_time() {
+    let mut s = session();
+    let r = s.execute("shape.insert", &json!({"preset": "rect", "rect": [80.0, 80.0, 420.0, 160.0], "text": "Big"})).unwrap();
+    let id = deckcraft_model::ShapeId(u32::try_from(r["id"].as_u64().unwrap()).unwrap());
+    let size = |s: &Session| s.doc().unwrap().shape(id).unwrap().text.as_ref().unwrap().paragraphs[0].runs[0].props.size;
+    s.execute("format.size", &json!({"size": 120})).unwrap();
+    let mut down = vec![];
+    for _ in 0..9 {
+        s.execute("format.shrink", &json!({})).unwrap();
+        down.push(size(&s).unwrap());
+    }
+    assert_eq!(down, [112.0, 104.0, 96.0, 88.0, 80.0, 72.0, 66.0, 60.0, 54.0]);
+    let mut up = vec![];
+    for _ in 0..7 {
+        s.execute("format.grow", &json!({})).unwrap();
+        up.push(size(&s).unwrap());
+    }
+    assert_eq!(up, [60.0, 66.0, 72.0, 80.0, 88.0, 96.0, 104.0]);
+    // A size between list steps goes to the next one down, and one past the top steps 8 at most.
+    s.execute("format.size", &json!({"size": 99})).unwrap();
+    s.execute("format.shrink", &json!({})).unwrap();
+    assert_eq!(size(&s), Some(96.0));
+    s.execute("format.size", &json!({"size": 150})).unwrap();
+    s.execute("format.shrink", &json!({})).unwrap();
+    assert_eq!(size(&s), Some(142.0));
+}
+
 /// A shape named many times in one edit is edited once and not copied per mention.
 #[test]
 fn repeated_target_ids_edit_the_shape_once() {

crates/ui-egui/src/ribbon/home.rs

@@ -197,7 +197,7 @@ fn font_group(app: &mut SlideApp, ui: &mut Ui, st: &Value) {
                 });
                 let size_text = size.map(|s| widgets::fmt_num(s, "")).unwrap_or_default();
                 dropdown(ui, "Font size", &size_text, 52.0, en, |ui| {
-                    for s in deckcraft_engine::cmd::format::SIZES.iter().chain([72.0, 80.0, 88.0, 96.0].iter()) {
+                    for s in deckcraft_engine::cmd::format::SIZES.iter() {
                         if ui.button(widgets::fmt_num(*s, "")).clicked() {
                             run(app, "format.size", json!({"size": s}));
                             ui.close();