Fix panic in feComposite arithmetic with oversized filter region

CHANGELOG.md

@@ -10,6 +10,9 @@ This changelog also contains important changes in dependencies.
 
 This release has an MSRV of 1.87.0 for `usvg` and `resvg` and the C API.
 
+### Fixed
+- Panic in `feComposite` with the `arithmetic` operator when the filter region is larger than the clamped layer. (#1021, #1007)
+
 ## [0.47.0] 2026-02-05
 
 This release has an MSRV of 1.87.0 for `usvg` and `resvg` and the C API.

crates/resvg/src/filter/mod.rs

@@ -365,6 +365,16 @@ fn apply_inner(
         .map(|r| r.to_int_rect())
         .ok_or(Error::InvalidRegion)?;
 
+    // The source pixmap is clamped to `max_bbox` in `render_group`, so the filter
+    // region (derived directly from the unclamped filter rect) can be larger than
+    // the buffer we actually render into. All intermediate filter images share the
+    // source's dimensions, so clamp the region to the source bounds to keep them
+    // consistent. Otherwise `feComposite` with the `arithmetic` operator, which
+    // requires equally sized inputs, would panic on a size mismatch.
+    let source_rect =
+        IntRect::from_xywh(0, 0, source.width(), source.height()).ok_or(Error::InvalidRegion)?;
+    let region = crate::geom::fit_to_rect(region, source_rect).ok_or(Error::InvalidRegion)?;
+
     let mut results: Vec<FilterResult> = Vec::new();
 
     for primitive in filter.primitives() {

crates/resvg/tests/integration/render.rs

@@ -81,6 +81,7 @@ use crate::render;
 #[test] fn filters_feComposite_invalid_operator() { assert_eq!(render("tests/filters/feComposite/invalid-operator"), 0); }
 #[test] fn filters_feComposite_operator_eq_arithmetic_and_invalid_k1_4() { assert_eq!(render("tests/filters/feComposite/operator=arithmetic-and-invalid-k1-4"), 0); }
 #[test] fn filters_feComposite_operator_eq_arithmetic_on_sRGB() { assert_eq!(render("tests/filters/feComposite/operator=arithmetic-on-sRGB"), 0); }
+#[test] fn filters_feComposite_operator_eq_arithmetic_with_huge_region() { assert_eq!(render("tests/filters/feComposite/operator=arithmetic-with-huge-region"), 0); }
 #[test] fn filters_feComposite_operator_eq_arithmetic_with_large_k1_4() { assert_eq!(render("tests/filters/feComposite/operator=arithmetic-with-large-k1-4"), 0); }
 #[test] fn filters_feComposite_operator_eq_arithmetic_with_opacity_on_sRGB() { assert_eq!(render("tests/filters/feComposite/operator=arithmetic-with-opacity-on-sRGB"), 0); }
 #[test] fn filters_feComposite_operator_eq_arithmetic_with_opacity() { assert_eq!(render("tests/filters/feComposite/operator=arithmetic-with-opacity"), 0); }