fix(render): key soft masks by inherited context (#716)

Co-authored-by: Brandon Thomas <echelon@gmail.com>

crates/render/src/raster.rs

@@ -1986,6 +1986,47 @@ trailer << /Root 1 0 R >>
         assert_ne!(second_pixel, [255, 255, 255, 255]);
     }
 
+    #[test]
+    fn shared_soft_mask_uses_each_inherited_resource_context() {
+        let page_body = "/A Do /B Do";
+        let form_a = "/GS gs 1 0 0 rg 0 0 40 40 re f";
+        let form_b = "/GS gs 0 0 1 rg 60 0 40 40 re f";
+        let mask_body = "/FILL Do";
+        let white = "1 g 0 0 100 100 re f";
+        let black = "0 g 0 0 100 100 re f";
+        let pdf = format!(
+            "%PDF-1.7\n\
+             1 0 obj << /Type /Catalog /Pages 2 0 R >> endobj\n\
+             2 0 obj << /Type /Pages /Kids [3 0 R] /Count 1 /MediaBox [0 0 100 100] >> endobj\n\
+             3 0 obj << /Type /Page /Parent 2 0 R /Resources << /XObject << /A 4 0 R /B 5 0 R >> >> /Contents 6 0 R >> endobj\n\
+             4 0 obj << /Type /XObject /Subtype /Form /BBox [0 0 100 100] /Resources << /ExtGState << /GS 8 0 R >> /XObject << /FILL 9 0 R >> >> /Length {} >> stream\n{form_a}\nendstream endobj\n\
+             5 0 obj << /Type /XObject /Subtype /Form /BBox [0 0 100 100] /Resources << /ExtGState << /GS 8 0 R >> /XObject << /FILL 10 0 R >> >> /Length {} >> stream\n{form_b}\nendstream endobj\n\
+             6 0 obj << /Length {} >> stream\n{page_body}\nendstream endobj\n\
+             8 0 obj << /Type /ExtGState /SMask 11 0 R >> endobj\n\
+             9 0 obj << /Type /XObject /Subtype /Form /BBox [0 0 100 100] /Length {} >> stream\n{white}\nendstream endobj\n\
+             10 0 obj << /Type /XObject /Subtype /Form /BBox [0 0 100 100] /Length {} >> stream\n{black}\nendstream endobj\n\
+             11 0 obj << /Type /Mask /S /Luminosity /G 12 0 R >> endobj\n\
+             12 0 obj << /Type /XObject /Subtype /Form /BBox [0 0 100 100] /Group << /S /Transparency /CS /DeviceGray >> /Length {} >> stream\n{mask_body}\nendstream endobj\n\
+             trailer << /Root 1 0 R >>\n%%EOF",
+            form_a.len(),
+            form_b.len(),
+            page_body.len(),
+            white.len(),
+            black.len(),
+            mask_body.len()
+        )
+        .into_bytes();
+        let mut renderer = PageRenderer::new(Arc::new(pdf), RenderConfig::default());
+        let page = renderer.render(RenderRequest { page: 0, scale: 1.0, ..Default::default() });
+        assert!(page.error.is_none(), "{:?}", page.error);
+        let pixel = |x: u32, y: u32| {
+            let offset = ((y * page.width + x) * 4) as usize;
+            [page.rgba[offset], page.rgba[offset + 1], page.rgba[offset + 2], page.rgba[offset + 3]]
+        };
+        assert_eq!(pixel(20, 80), [255, 0, 0, 255], "the white inherited mask makes form A visible");
+        assert_eq!(pixel(80, 80), [255, 255, 255, 255], "the black inherited mask must not reuse form A's cached pixels");
+    }
+
     #[test]
     fn renders_a_blue_rectangle() {
         let pool = RenderPool::new(Arc::new(ONE_PAGE.to_vec()), 1, RenderConfig::default());

vendor/hayro-interpret/src/soft_mask.rs

@@ -48,6 +48,7 @@ impl TransferFunction {
 }
 
 struct Repr<'a> {
+    cache_key: u128,
     obj_id: ObjectIdentifier,
     group: FormXObject<'a>,
     mask_type: MaskType,
@@ -65,7 +66,6 @@ struct Repr<'a> {
 impl Hash for Repr<'_> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.obj_id.hash(state);
-        self.root_transform.cache_key().hash(state);
     }
 }
 
@@ -89,7 +89,7 @@ impl Eq for SoftMask<'_> {}
 
 impl CacheKey for SoftMask<'_> {
     fn cache_key(&self) -> u128 {
-        hash128(self)
+        self.0.cache_key
     }
 }
 
@@ -134,12 +134,23 @@ impl<'a> SoftMask<'a> {
             _ => return None,
         };
         let nesting_depth = context.nesting_depth() + 1;
+        let root_transform = context.get().ctm;
+        let bbox = context.bbox();
+        let resources_key = resources_cache_key(&parent_resources);
+        let cache_key = hash128(&(
+            dict.cache_key(),
+            root_transform.cache_key(),
+            [bbox.x0.to_bits(), bbox.y0.to_bits(), bbox.x1.to_bits(), bbox.y1.to_bits()],
+            resources_key,
+            nesting_depth,
+        ));
 
         Some(Self(Rc::new(Repr {
+            cache_key,
             obj_id,
             group,
             mask_type,
-            root_transform: context.get().ctm,
+            root_transform,
             transfer_function,
             bbox: context.bbox(),
             interpreter_cache: context.interpreter_cache.clone(),
@@ -188,3 +199,16 @@ impl<'a> SoftMask<'a> {
         self.0.transfer_function.as_ref()
     }
 }
+
+fn resources_cache_key(resources: &Resources<'_>) -> u128 {
+    let local = (
+        resources.ext_g_states.obj_id(),
+        resources.fonts.obj_id(),
+        resources.properties.obj_id(),
+        resources.color_spaces.obj_id(),
+        resources.x_objects.obj_id(),
+        resources.patterns.obj_id(),
+        resources.shadings.obj_id(),
+    );
+    hash128(&(local, resources.parent().map(resources_cache_key)))
+}