[librsvg: 4/5] (#560): Ignore missing filter definitions instead of not rendering the filtered object

[Federico Mena Quintero <federico src gnome org>]

commit d05fc806d152525c8611042a224e683ae4a97aad
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed Aug 19 20:06:02 2020 -0500

    (#560): Ignore missing filter definitions instead of not rendering the filtered object
    
    This is a change from the behavior we had for SVG 1.1.
    
    SVG1.1 doesn't mention what to do when there is an element with a
    filter="url(#nonexistent)" attribute, i.e. when it points to a
    nonexistent element or when the element is not a <filter> element.
    However, the SVG1.1 test suite implies (in the files removed by this
    commit) that the object being filtered should not be rendered at all.
    
    However, SVG2 *does* mention what to do in
    https://www.w3.org/TR/filter-effects/#FilterProperty - the object
    being filtered should get no filter applied, i.e. render it as if it
    had no filter.
    
    Fixes https://gitlab.gnome.org/GNOME/librsvg/-/issues/560

 librsvg_crate/tests/bugs.rs       | 44 +++++++++++++++++++++++++++++++++++++++
 rsvg_internals/src/drawing_ctx.rs | 10 +++------
 2 files changed, 47 insertions(+), 7 deletions(-)
---
diff --git a/librsvg_crate/tests/bugs.rs b/librsvg_crate/tests/bugs.rs
index 33aa96602..2b1856ff4 100644
--- a/librsvg_crate/tests/bugs.rs
+++ b/librsvg_crate/tests/bugs.rs
@@ -127,3 +127,47 @@ fn href_attribute_overrides_xlink_href() {
         "href_attribute_overrides_xlink_href",
     );
 }
+
+// https://gitlab.gnome.org/GNOME/librsvg/-/issues/560
+#[test]
+fn nonexistent_filter_leaves_object_unfiltered() {
+    let svg = load_svg(
+        br##"<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg";
+     width="500" height="500">
+  <rect x="100" y="100" width="100" height="100" fill="lime" filter="url(#nonexistent)"/>
+</svg>
+"##,
+    );
+
+    let output_surf = render_document(
+        &svg,
+        SurfaceSize(500, 500),
+        |_| (),
+        cairo::Rectangle {
+            x: 0.0,
+            y: 0.0,
+            width: 500.0,
+            height: 500.0,
+        },
+    )
+    .unwrap();
+
+    let reference_surf = cairo::ImageSurface::create(cairo::Format::ARgb32, 500, 500).unwrap();
+
+    {
+        let cr = cairo::Context::new(&reference_surf);
+
+        cr.rectangle(100.0, 100.0, 100.0, 100.0);
+        cr.set_source_rgba(0.0, 1.0, 0.0, 1.0);
+        cr.fill();
+    }
+
+    let reference_surf = SharedImageSurface::wrap(reference_surf, SurfaceType::SRgb).unwrap();
+
+    compare_to_surface(
+        &output_surf,
+        &reference_surf,
+        "nonexistent_filter_leaves_object_unfiltered",
+    );
+}
diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index d22633372..b98f7c741 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -783,7 +783,7 @@ impl DrawingCtx {
                     }
                     _ => {
                         rsvg_log!(
-                            "element {} will not be rendered since \"{}\" is not a filter",
+                            "element {} will not be filtered since \"{}\" is not a filter",
                             node,
                             filter_uri,
                         );
@@ -792,7 +792,7 @@ impl DrawingCtx {
             }
             _ => {
                 rsvg_log!(
-                    "element {} will not be rendered since its filter \"{}\" was not found",
+                    "element {} will not be filtered since its filter \"{}\" was not found",
                     node,
                     filter_uri,
                 );
@@ -800,11 +800,7 @@ impl DrawingCtx {
         }
 
         // Non-existing filters must act as null filters (an empty surface is returned).
-        Ok(SharedImageSurface::empty(
-            child_surface.width(),
-            child_surface.height(),
-            child_surface.surface_type(),
-        )?)
+        Ok(child_surface.clone())
     }
 
     fn set_color(