address review: skip the image cache for resource-dependent names inside colour-space arrays

crates/pdf/src/color.rs

@@ -94,6 +94,28 @@ pub fn color_space(file: &File, o: &Obj, res: Option<&Dict>) -> Cs {
     color_space_at(file, o, res, 0)
 }
 
+/// Whether decoding colour space `o` looks a name up in the page resources: a name that is not a
+/// device space, anywhere in the definition (an Indexed base, a Separation or DeviceN alternate, an
+/// ICCBased alternate). The same image then decodes differently under different resources.
+pub fn names_resource(file: &File, o: &Obj, depth: usize) -> bool {
+    if depth >= MAX_DEPTH {
+        return true;
+    }
+    match file.resolve(o) {
+        Obj::Name(n) => !matches!(n.as_str(), "DeviceGray" | "DeviceRGB" | "DeviceCMYK" | "G" | "RGB" | "CMYK"),
+        Obj::Array(a) => {
+            let inner = match a.first().map(|h| file.resolve(h)).and_then(Obj::name).unwrap_or("") {
+                "Indexed" | "I" => a.get(1).cloned(),
+                "Separation" | "DeviceN" => a.get(2).cloned(),
+                "ICCBased" => a.get(1).map(|s| file.resolve(s)).and_then(Obj::dict).and_then(|d| file.get(d, "Alternate")).cloned(),
+                _ => None,
+            };
+            inner.is_some_and(|i| names_resource(file, &i, depth + 1))
+        }
+        _ => false,
+    }
+}
+
 /// [`color_space`] nested `depth` levels deep: DeviceGray past [`MAX_DEPTH`].
 fn color_space_at(file: &File, o: &Obj, res: Option<&Dict>, depth: usize) -> Cs {
     if depth >= MAX_DEPTH {

crates/pdf/src/page.rs

@@ -13,7 +13,7 @@ use effectcraft_svg::{
 use kurbo::{Point, Shape as _};
 
 use crate::build::{Builder, MAX_PATH};
-use crate::color::{Cs, Func, color_space, text_string};
+use crate::color::{Cs, Func, color_space, names_resource, text_string};
 use crate::font::Font;
 use crate::object::{Dict, File, Lexer, Obj, decode_stream};
 
@@ -1054,10 +1054,9 @@ impl<'a> Interp<'a> {
             Fill::Color(c) => *c,
             _ => [0.0; 3],
         };
-        // A named colour space other than a device one is looked up in `res`, which differs
-        // between placements, so those images are decoded each time.
-        let named_space =
-            self.file.get(d, "ColorSpace").and_then(Obj::name).is_some_and(|n| !matches!(n, "DeviceGray" | "DeviceRGB" | "DeviceCMYK" | "G" | "RGB" | "CMYK"));
+        // A named colour space other than a device one, even inside an array, is looked up in
+        // `res`, which differs between placements, so those images are decoded each time.
+        let named_space = self.file.get(d, "ColorSpace").is_some_and(|c| names_resource(self.file, c, 0));
         let cache_key = key.filter(|_| !named_space).map(|k| (k, fill.map(|x| (x.clamp(0.0, 1.0) * 255.0).round() as u8)));
         let decoded = match cache_key.as_ref().and_then(|k| self.images.get(k)) {
             Some(img) => img.clone(),

crates/pdf/src/tests/import.rs

@@ -699,3 +699,29 @@ fn an_image_with_a_named_colour_space_is_not_shared_between_resource_dictionarie
     assert_eq!(found.len(), 2, "{:?}", doc.skipped);
     assert_ne!(found[0].rgba, found[1].rgba, "each placement is decoded with its own colour space");
 }
+
+#[test]
+fn an_image_with_a_named_base_inside_an_array_is_not_shared_between_resource_dictionaries() {
+    fn images<'a>(g: &'a effectcraft_svg::Group, out: &mut Vec<&'a effectcraft_svg::Image>) {
+        for n in &g.children {
+            match n {
+                Node::Group(g) => images(g, out),
+                Node::Image(i) => out.push(i),
+                Node::Shape(_) => {}
+            }
+        }
+    }
+    let form = |space: &str| {
+        format!("<< /Type /XObject /Subtype /Form /BBox [0 0 200 100] /Resources << /XObject << /Im 10 0 R >> /ColorSpace << /CS1 /{space} >> >> >>")
+    };
+    let objs = vec![
+        (10, "<< /Type /XObject /Subtype /Image /Width 1 /Height 1 /ColorSpace [/Indexed /CS1 0 <0A141E>] /BitsPerComponent 8 >>".into(), Some(vec![0])),
+        (11, form("DeviceGray"), Some(b"/Im Do".to_vec())),
+        (12, form("DeviceRGB"), Some(b"/Im Do".to_vec())),
+    ];
+    let doc = parse(&page_pdf("/FA Do /FB Do", "/XObject << /FA 11 0 R /FB 12 0 R >>", objs)).unwrap();
+    let mut found = vec![];
+    images(&doc.root, &mut found);
+    assert_eq!(found.len(), 2, "{:?}", doc.skipped);
+    assert_ne!(found[0].rgba, found[1].rgba, "each placement is decoded with its own colour space");
+}