From 29c38887deeb748f32e14b482a15304f81777558 Mon Sep 17 00:00:00 2001
From: MarekSpodBiedry <73122968+MarekSpodBiedry@users.noreply.github.com>
Date: Tue, 13 Oct 2026 18:03:44 +0200
Subject: [PATCH] Keep chart cache point positions when a reference has blank
 edges (#1015)

---
 crates/xlsx/src/chart.rs                   |  9 ++++++--
 crates/xlsx/src/tests/chart_ref_offsets.rs | 25 ++++++++++++++++++++++
 crates/xlsx/src/tests/mod.rs               |  1 +
 3 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 crates/xlsx/src/tests/chart_ref_offsets.rs

diff --git a/crates/xlsx/src/chart.rs b/crates/xlsx/src/chart.rs
index dee33c83d..c93377ca6 100644
--- a/crates/xlsx/src/chart.rs
+++ b/crates/xlsx/src/chart.rs
@@ -292,9 +292,14 @@ pub(crate) fn ref_values(wb: &Workbook, sheet_idx: usize, f: &str) -> Option<Vec
     };
     let sheet = wb.sheet(si)?;
     let mut range = r.range();
-    // Whole columns/rows: limit to the used range.
+    // Whole columns/rows: cut the far end at the used range. The start stays put, so point indices keep matching the reference.
     if let Some(u) = sheet.used_range() {
-        range = range.intersection(&u)?;
+        if range.is_full_cols() {
+            range.end.row = range.end.row.min(u.end.row.max(range.start.row));
+        }
+        if range.is_full_rows() {
+            range.end.col = range.end.col.min(u.end.col.max(range.start.col));
+        }
     }
     if range.count() > MAX_CACHE {
         return None;
diff --git a/crates/xlsx/src/tests/chart_ref_offsets.rs b/crates/xlsx/src/tests/chart_ref_offsets.rs
new file mode 100644
index 000000000..87e6ba9fa
--- /dev/null
+++ b/crates/xlsx/src/tests/chart_ref_offsets.rs
@@ -0,0 +1,25 @@
+//! Chart caches keep the position of every point inside the referenced range.
+
+use gridcraft_core::{CellRef, Value};
+use gridcraft_model::{Sheet, Workbook};
+use std::sync::Arc;
+
+use crate::chart::ref_values;
+
+fn book() -> Workbook {
+    let mut s = Sheet::new("Data");
+    s.set_value(CellRef::new(3, 0), Value::Number(5.0));
+    Workbook { sheets: vec![Arc::new(s)], ..Workbook::default() }
+}
+
+#[test]
+fn explicit_range_keeps_leading_and_trailing_blanks() {
+    let vals = ref_values(&book(), 0, "Data!$A$3:$A$6").unwrap();
+    assert_eq!(vals, vec![Value::Empty, Value::Number(5.0), Value::Empty, Value::Empty]);
+}
+
+#[test]
+fn whole_column_still_stops_at_used_range_and_starts_at_top() {
+    let vals = ref_values(&book(), 0, "Data!$A:$A").unwrap();
+    assert_eq!(vals, vec![Value::Empty, Value::Empty, Value::Empty, Value::Number(5.0)]);
+}
diff --git a/crates/xlsx/src/tests/mod.rs b/crates/xlsx/src/tests/mod.rs
index 517113d0f..afa2247de 100644
--- a/crates/xlsx/src/tests/mod.rs
+++ b/crates/xlsx/src/tests/mod.rs
@@ -2,6 +2,7 @@
 
 mod array_export;
 mod chart_bool_default;
+mod chart_ref_offsets;
 mod csv_tests;
 mod encrypted_tests;
 mod fixtures;