From 735e16d93c33a9d480dfcf055c5373402fb1bdfb Mon Sep 17 00:00:00 2001
From: Brandon Thomas <echelon@gmail.com>
Date: Tue, 13 Oct 2026 04:30:41 -0400
Subject: [PATCH] Charts: text at the sizes the file sets, as in PowerPoint
 (#358)

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 crates/model/src/chart.rs     |  9 ++++++
 crates/pptx/src/read/chart.rs | 52 +++++++++++++++++++++++++++++++++++
 crates/render/src/chart.rs    |  9 ++++--
 3 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/crates/model/src/chart.rs b/crates/model/src/chart.rs
index e83e1ed..aebee49 100644
--- a/crates/model/src/chart.rs
+++ b/crates/model/src/chart.rs
@@ -150,6 +150,13 @@ pub struct Chart {
     pub legend: Option<String>,
     /// `c:legend/c:overlay`: the legend is drawn over the plot instead of shrinking it.
     pub legend_overlay: bool,
+    /// Text size in points of the axis labels and legend (from their `c:txPr`, else the chart's);
+    /// `None`: the file gives none.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub text_size: Option<f64>,
+    /// Title text size in points (its rich text or `c:txPr`).
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub title_size: Option<f64>,
     pub data_labels: bool,
     pub gridlines: bool,
     pub axis_titles: (Option<String>, Option<String>),
@@ -193,6 +200,8 @@ impl Default for Chart {
             series: vec![],
             legend: Some("b".into()),
             legend_overlay: false,
+            text_size: None,
+            title_size: None,
             data_labels: false,
             gridlines: true,
             axis_titles: (None, None),
diff --git a/crates/pptx/src/read/chart.rs b/crates/pptx/src/read/chart.rs
index 8d2cb59..6d7541f 100644
--- a/crates/pptx/src/read/chart.rs
+++ b/crates/pptx/src/read/chart.rs
@@ -277,9 +277,35 @@ pub(crate) fn chart_from(root: &El) -> Option<Chart> {
     if let Some(a) = cat_ax {
         c.axis_titles.0 = a.child("title").map(|t| rich_text(t).unwrap_or_else(|| "Axis Title".into()));
     }
+    // Text sizes as the file sets them (PowerPoint draws chart text at these sizes, not scaled to
+    // the chart): the axes' and legend's, else the whole chart's; the title's own.
+    let chart_size = text_size(root.child("txPr"));
+    c.text_size = [val_ax, cat_ax, ch.child("legend")].into_iter().flatten().find_map(|e| text_size(e.child("txPr"))).or(chart_size);
+    c.title_size = ch.child("title").and_then(|t| text_size(t.child("tx").and_then(|x| x.child("rich"))).or_else(|| text_size(t.child("txPr"))));
     Some(c)
 }
 
+/// The size in points of the first `a:defRPr` or `a:rPr` with one under `e` (`sz` in hundredths).
+fn text_size(e: Option<&El>) -> Option<f64> {
+    fn rec(e: &El, depth: usize) -> Option<f64> {
+        if depth > 8 {
+            return None;
+        }
+        for c in e.elements() {
+            if (c.is("defRPr") || c.is("rPr"))
+                && let Some(v) = c.attr("sz").and_then(|v| v.parse::<f64>().ok()).filter(|v| v.is_finite() && *v > 0.0)
+            {
+                return Some((v / 100.0).clamp(1.0, 400.0));
+            }
+            if let Some(v) = rec(c, depth + 1) {
+                return Some(v);
+            }
+        }
+        None
+    }
+    rec(e?, 0)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -336,4 +362,30 @@ mod tests {
         let c = read_chart_xml(single.as_bytes()).unwrap();
         assert!(c.series.iter().all(|s| !s.secondary_axis));
     }
+
+    #[test]
+    fn text_sizes_are_read_from_the_file() {
+        // PowerPoint's new charts set the axes' and legend's text to 11.97 pt and the title's to
+        // 18.62 pt; a chart that only sets its overall text size uses it everywhere.
+        let ns =
+            r#"xmlns:c="http://schemas.openxmlformats.org/drawingml/2006/chart" xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main""#;
+        let tx = |sz: u32| format!(r#"<c:txPr><a:bodyPr/><a:p><a:pPr><a:defRPr sz="{sz}"/></a:pPr></a:p></c:txPr>"#);
+        let xml = format!(
+            r#"<c:chartSpace {ns}><c:chart><c:title><c:tx><c:rich><a:bodyPr/><a:p><a:pPr><a:defRPr sz="1862"/></a:pPr><a:r><a:t>T</a:t></a:r></a:p></c:rich></c:tx></c:title><c:plotArea><c:barChart><c:barDir val="col"/><c:axId val="1"/><c:axId val="2"/></c:barChart><c:catAx><c:axId val="1"/>{}</c:catAx><c:valAx><c:axId val="2"/>{}</c:valAx></c:plotArea></c:chart></c:chartSpace>"#,
+            tx(1197),
+            tx(1197)
+        );
+        let c = read_chart_xml(xml.as_bytes()).unwrap();
+        assert_eq!((c.text_size, c.title_size), (Some(11.97), Some(18.62)));
+        let xml = format!(
+            r#"<c:chartSpace {ns}><c:chart><c:plotArea><c:barChart><c:barDir val="col"/></c:barChart></c:plotArea></c:chart>{}</c:chartSpace>"#,
+            tx(1400)
+        );
+        let c = read_chart_xml(xml.as_bytes()).unwrap();
+        assert_eq!((c.text_size, c.title_size), (Some(14.0), None));
+        let xml = format!(
+            r#"<c:chartSpace {ns}><c:chart><c:plotArea><c:barChart><c:barDir val="col"/></c:barChart></c:plotArea></c:chart></c:chartSpace>"#
+        );
+        assert_eq!(read_chart_xml(xml.as_bytes()).unwrap().text_size, None, "no sizes: the renderer picks one");
+    }
 }
diff --git a/crates/render/src/chart.rs b/crates/render/src/chart.rs
index f8417aa..eb2b0a9 100644
--- a/crates/render/src/chart.rs
+++ b/crates/render/src/chart.rs
@@ -139,11 +139,14 @@ pub fn draw(ctx: &mut RenderContext, rctx: &Ctx, c: &Chart, m: Affine, w: f64, h
             rctx.pres,
         );
     }
-    let base = (h.min(w) / 22.0).clamp(7.0, 18.0);
+    // The file's text sizes when it has them (PowerPoint draws chart text at them); otherwise a size
+    // that suits the chart.
+    let base = c.text_size.unwrap_or_else(|| (h.min(w) / 22.0).clamp(7.0, 18.0));
+    let title_size = c.title_size.unwrap_or(base * 1.4);
     let mut area = Rect::new(w * 0.04, h * 0.04, w * 0.96, h * 0.96);
     if let Some(t) = &c.title {
-        label(ctx, rctx, m, t, Rect::new(0.0, area.y0, w, area.y0 + base * 1.8), base * 1.4, Align::Center, Anchor::Top, text_col, false);
-        area.y0 += base * 2.4;
+        label(ctx, rctx, m, t, Rect::new(0.0, area.y0, w, area.y0 + title_size * 1.3), title_size, Align::Center, Anchor::Top, text_col, false);
+        area.y0 += title_size * 1.7;
     }
     let pie = matches!(c.kind, ChartType::Pie | ChartType::Doughnut);
     // Legend placed by `c:legendPos`.