Drawing: share length display formatting (#2054) (#2086)

Thanks @0xlillith.

crates/doc/src/display_units.rs

@@ -0,0 +1,123 @@
+//! The existing length display policy, shared by windowed and headless consumers.
+//!
+//! Values are stored in millimetres and displayed in the five design units. Unknown unit
+//! names retain the millimetre fallback; expression units have a separate, broader vocabulary.
+//! These functions format values, not validate them: non-finite inputs retain Rust's `NaN`,
+//! `inf` and `-inf` text. Callers that require finite measurements must validate them first.
+
+/// Units per millimetre and the unit's name. Unknown names use millimetres.
+pub fn unit_scale(units: &str) -> (f64, &'static str) {
+    match units {
+        "cm" => (0.1, "cm"),
+        "m" => (0.001, "m"),
+        "in" => (1.0 / 25.4, "in"),
+        "ft" => (1.0 / 304.8, "ft"),
+        _ => (1.0, "mm"),
+    }
+}
+
+/// Inch labels retain a meaningful fourth digit without promoting floating-point noise.
+/// `value` is already converted to the requested display unit, not a millimetre value.
+pub fn length_precision(value: f64, units: &str, decimals: u8) -> usize {
+    let base = usize::from(decimals.min(8));
+    if units != "in" {
+        return base;
+    }
+    let needs_four = ((value * 10_000.0).round() - (value * 1000.0).round() * 10.0).abs() >= 0.5;
+    base.max(if needs_four { 4 } else { 3 })
+}
+
+/// A millimetre length in the requested display unit, without a unit suffix.
+pub fn length_number(mm: f64, units: &str, decimals: u8) -> String {
+    let value = mm * unit_scale(units).0;
+    format!("{:.*}", length_precision(value, units, decimals), value)
+}
+
+/// A length in millimetres in `units`, with `decimals` (for display).
+pub fn format_length(mm: f64, units: &str, decimals: u8) -> String {
+    let (_, u) = unit_scale(units);
+    format!("{} {u}", length_number(mm, units, decimals))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{format_length, length_number, length_precision, unit_scale};
+
+    #[test]
+    fn all_design_units_keep_bare_and_suffixed_labels() {
+        for (mm, units, bare, suffixed) in [
+            (12.5, "mm", "12.50", "12.50 mm"),
+            (125.0, "cm", "12.50", "12.50 cm"),
+            (12_500.0, "m", "12.50", "12.50 m"),
+            (317.5, "in", "12.500", "12.500 in"),
+            (3810.0, "ft", "12.50", "12.50 ft"),
+        ] {
+            assert_eq!(length_number(mm, units, 2), bare, "{units}");
+            assert_eq!(format_length(mm, units, 2), suffixed, "{units}");
+        }
+    }
+
+    #[test]
+    fn inch_labels_keep_three_or_four_digits_without_promoting_noise() {
+        for (mm, decimals, expected) in [
+            (25.4, 0, "1.000"),
+            (25.4 * 1.234, 2, "1.234"),
+            (25.4 * 1.2345, 0, "1.2345"),
+            (-25.4 * 1.2345, 3, "-1.2345"),
+            (25.4 * 0.001, 2, "0.001"),
+            (25.4 * (1.0 + 1e-12), 2, "1.000"),
+            (25.4, 4, "1.0000"),
+            (25.4, 5, "1.00000"),
+            (0.0, 0, "0.000"),
+        ] {
+            assert_eq!(length_number(mm, "in", decimals), expected, "{mm} mm, {decimals} places");
+        }
+    }
+
+    #[test]
+    fn precision_uses_the_converted_value_and_caps_requested_places() {
+        assert_eq!(length_precision(1.2345, "in", 2), 4);
+        assert_eq!(length_precision(1.234, "in", 2), 3);
+        assert_eq!(length_precision(1.2345, "mm", 2), 2);
+        assert_eq!(length_precision(1.2345, "in", 6), 6);
+        assert_eq!(length_precision(1.2345, "in", u8::MAX), 8);
+        assert_eq!(length_precision(1.2345, "mm", u8::MAX), 8);
+        assert_eq!(length_number(12.5, "mm", u8::MAX), "12.50000000");
+        assert_eq!(length_number(25.4, "in", u8::MAX), "1.00000000");
+    }
+
+    #[test]
+    fn rounding_and_signed_zero_keep_the_existing_display_policy() {
+        for (mm, decimals, expected) in [
+            (0.0, 2, "0.00"),
+            (-0.0, 2, "-0.00"),
+            (-0.0001, 2, "-0.00"),
+            (-12.5, 2, "-12.50"),
+            (12.5, 0, "12"),
+            (13.5, 0, "14"),
+            (-12.5, 0, "-12"),
+            (-13.5, 0, "-14"),
+            (1.25, 1, "1.2"),
+            (1.75, 1, "1.8"),
+        ] {
+            assert_eq!(length_number(mm, "mm", decimals), expected, "{mm} mm, {decimals} places");
+        }
+        assert_eq!(format_length(-0.0, "in", 2), "-0.000 in");
+    }
+
+    #[test]
+    fn unknown_display_units_keep_the_millimetre_fallback() {
+        for units in ["", "inch", " in ", "IN", "unsupported"] {
+            assert_eq!(unit_scale(units), (1.0, "mm"), "{units}");
+            assert_eq!(length_number(25.4, units, 2), "25.40", "{units}");
+            assert_eq!(format_length(25.4, units, 2), "25.40 mm", "{units}");
+        }
+    }
+
+    #[test]
+    fn non_finite_text_is_preserved_without_claiming_validation() {
+        assert_eq!(length_number(f64::NAN, "mm", 2), "NaN");
+        assert_eq!(format_length(f64::INFINITY, "in", u8::MAX), "inf in");
+        assert_eq!(format_length(f64::NEG_INFINITY, "cm", 2), "-inf cm");
+    }
+}

crates/doc/src/lib.rs

@@ -17,6 +17,7 @@ pub use clipboard::{clone_expression, remap_topology};
 pub mod config;
 pub mod construct;
 pub mod display_quality;
+pub mod display_units;
 mod document;
 mod eval;
 pub mod expr;

crates/ui-egui/src/prefs.rs

@@ -11,6 +11,7 @@
 use egui::{Modifiers, Pos2, RichText};
 use serde::{Deserialize, Serialize};
 use serde_json::json;
+pub use solidcraft_engine::doc::display_units::{format_length, length_number, length_precision, unit_scale};
 use solidcraft_engine::geom::Vec3;
 
 /// The key the apps keep the preferences under in eframe's storage.
@@ -748,32 +749,6 @@ pub(crate) fn pivot_under(app: &SolveApp, proj: &crate::viewport::Proj, at: Pos2
     if b.is_empty() { app.cam.target } else { b.center() }
 }
 
-/// Units per millimetre and the unit's name.
-pub fn unit_scale(units: &str) -> (f64, &'static str) {
-    match units {
-        "cm" => (0.1, "cm"),
-        "m" => (0.001, "m"),
-        "in" => (1.0 / 25.4, "in"),
-        "ft" => (1.0 / 304.8, "ft"),
-        _ => (1.0, "mm"),
-    }
-}
-
-/// Inch labels retain a meaningful fourth digit without promoting floating-point noise.
-pub fn length_precision(value: f64, units: &str, decimals: u8) -> usize {
-    let base = usize::from(decimals.min(8));
-    if units != "in" {
-        return base;
-    }
-    let needs_four = ((value * 10_000.0).round() - (value * 1000.0).round() * 10.0).abs() >= 0.5;
-    base.max(if needs_four { 4 } else { 3 })
-}
-
-pub fn length_number(mm: f64, units: &str, decimals: u8) -> String {
-    let value = mm * unit_scale(units).0;
-    format!("{:.*}", length_precision(value, units, decimals), value)
-}
-
 /// A plain number typed into a field, with a decimal point or a decimal comma (#1347): "2.5"
 /// and "2,5" are both 2.5, as a numeric keypad types either depending on the locale. Spaces are
 /// ignored and "−" is a minus, as in egui's own parser. A comma beside a point ("1.234,5") or a
@@ -808,12 +783,6 @@ pub fn parse_length_mm(text: &str, scale: f64) -> Option<f64> {
     value.is_finite().then_some(value)
 }
 
-/// A length in millimetres in `units`, with `decimals` (for display).
-pub fn format_length(mm: f64, units: &str, decimals: u8) -> String {
-    let (_, u) = unit_scale(units);
-    format!("{} {u}", length_number(mm, units, decimals))
-}
-
 /// A length, area (`power` 2) or volume (3) given in millimetres, shown in the design's units
 /// with the length precision.
 pub fn show_mm(app: &SolveApp, v: f64, power: i32) -> String {