(#743): implement the feDropShadow element

Fixes https://gitlab.gnome.org/GNOME/librsvg/-/issues/743

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/793>

7 files changed, 136 insertions, 2 deletions

diff --git a/Makefile.am b/Makefile.am
index ac169ee9..24e47b34 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -63,6 +63,7 @@ LIBRSVG_SRC =					\
 	src/filters/context.rs			\
 	src/filters/convolve_matrix.rs		\
 	src/filters/displacement_map.rs		\
+	src/filters/drop_shadow.rs		\
 	src/filters/error.rs			\
 	src/filters/flood.rs			\
 	src/filters/gaussian_blur.rs		\
diff --git a/src/element.rs b/src/element.rs
index bf5c1a30..2ee4e693 100644
--- a/src/element.rs
+++ b/src/element.rs
@@ -21,6 +21,7 @@ use crate::filters::{
     composite::FeComposite,
     convolve_matrix::FeConvolveMatrix,
     displacement_map::FeDisplacementMap,
+    drop_shadow::FeDropShadow,
     flood::FeFlood,
     gaussian_blur::FeGaussianBlur,
     image::FeImage,
@@ -315,6 +316,7 @@ pub enum Element {
     FeDiffuseLighting(Box<ElementInner<FeDiffuseLighting>>),
     FeDisplacementMap(Box<ElementInner<FeDisplacementMap>>),
     FeDistantLight(Box<ElementInner<FeDistantLight>>),
+    FeDropShadow(Box<ElementInner<FeDropShadow>>),
     FeFlood(Box<ElementInner<FeFlood>>),
     FeFuncA(Box<ElementInner<FeFuncA>>),
     FeFuncB(Box<ElementInner<FeFuncB>>),
@@ -372,6 +374,7 @@ macro_rules! call_inner {
             Element::FeDiffuseLighting(i) => i.$method($($args),*),
             Element::FeDisplacementMap(i) => i.$method($($args),*),
             Element::FeDistantLight(i) => i.$method($($args),*),
+            Element::FeDropShadow(i) => i.$method($($args),*),
             Element::FeFlood(i) => i.$method($($args),*),
             Element::FeFuncA(i) => i.$method($($args),*),
             Element::FeFuncB(i) => i.$method($($args),*),
@@ -494,6 +497,7 @@ impl Element {
             Element::FeConvolveMatrix(ref fe) => Some(&fe.element_impl),
             Element::FeDiffuseLighting(ref fe) => Some(&fe.element_impl),
             Element::FeDisplacementMap(ref fe) => Some(&fe.element_impl),
+            Element::FeDropShadow(ref fe) => Some(&fe.element_impl),
             Element::FeFlood(ref fe) => Some(&fe.element_impl),
             Element::FeGaussianBlur(ref fe) => Some(&fe.element_impl),
             Element::FeImage(ref fe) => Some(&fe.element_impl),
@@ -591,8 +595,9 @@ mod creators {
     e!(create_fe_composite,             FeComposite);
     e!(create_fe_convolve_matrix,       FeConvolveMatrix);
     e!(create_fe_diffuse_lighting,      FeDiffuseLighting);
-    e!(create_fe_distant_light,         FeDistantLight);
     e!(create_fe_displacement_map,      FeDisplacementMap);
+    e!(create_fe_distant_light,         FeDistantLight);
+    e!(create_fe_drop_shadow,           FeDropShadow);
     e!(create_fe_flood,                 FeFlood);
     e!(create_fe_gaussian_blur,         FeGaussianBlur);
     e!(create_fe_image,                 FeImage);
@@ -685,6 +690,7 @@ static ELEMENT_CREATORS: Lazy<HashMap<&'static str, (ElementCreateFn, ElementCre
         ("feDiffuseLighting",   create_fe_diffuse_lighting,   Default),
         ("feDisplacementMap",   create_fe_displacement_map,   Default),
         ("feDistantLight",      create_fe_distant_light,      IgnoreClass),
+        ("feDropShadow",        create_fe_drop_shadow,        Default),
         ("feFuncA",             create_fe_func_a,             IgnoreClass),
         ("feFuncB",             create_fe_func_b,             IgnoreClass),
         ("feFuncG",             create_fe_func_g,             IgnoreClass),
@@ -788,6 +794,7 @@ mod sizes {
         print_size!(FeDiffuseLighting);
         print_size!(FeDistantLight);
         print_size!(FeDisplacementMap);
+        print_size!(FeDropShadow);
         print_size!(FeFlood);
         print_size!(FeGaussianBlur);
         print_size!(FeImage);
diff --git a/src/filters/drop_shadow.rs b/src/filters/drop_shadow.rs
new file mode 100644
index 00000000..3969d5e5
--- /dev/null
+++ b/src/filters/drop_shadow.rs
@@ -0,0 +1,88 @@
+use markup5ever::{expanded_name, local_name, namespace_url, ns};
+
+use crate::document::AcquiredNodes;
+use crate::element::{set_attribute, SetAttributes};
+use crate::filter_func::drop_shadow_primitives;
+use crate::node::{CascadedValues, Node};
+use crate::paint_server::resolve_color;
+use crate::parsers::{NumberOptionalNumber, ParseValue};
+use crate::session::Session;
+use crate::xml::Attributes;
+
+use super::{FilterEffect, FilterResolveError, Input, Primitive, ResolvedPrimitive};
+
+/// The `feDropShadow` element.
+#[derive(Default)]
+pub struct FeDropShadow {
+    base: Primitive,
+    params: DropShadow,
+}
+
+/// Resolved `feDropShadow` parameters for rendering.
+#[derive(Clone)]
+pub struct DropShadow {
+    pub in1: Input,
+    pub dx: f64,
+    pub dy: f64,
+    pub std_deviation: NumberOptionalNumber<f64>,
+}
+
+impl Default for DropShadow {
+    /// Defaults come from https://www.w3.org/TR/filter-effects/#feDropShadowElement
+    fn default() -> Self {
+        Self {
+            in1: Default::default(),
+            dx: 2.0,
+            dy: 2.0,
+            std_deviation: NumberOptionalNumber(2.0, 2.0),
+        }
+    }
+}
+
+impl SetAttributes for FeDropShadow {
+    fn set_attributes(&mut self, attrs: &Attributes, session: &Session) {
+        self.params.in1 = self.base.parse_one_input(attrs, session);
+
+        for (attr, value) in attrs.iter() {
+            match attr.expanded() {
+                expanded_name!("", "dx") => {
+                    set_attribute(&mut self.params.dx, attr.parse(value), session);
+                }
+
+                expanded_name!("", "dy") => {
+                    set_attribute(&mut self.params.dy, attr.parse(value), session);
+                }
+
+                expanded_name!("", "stdDeviation") => {
+                    set_attribute(&mut self.params.std_deviation, attr.parse(value), session);
+                }
+
+                _ => (),
+            }
+        }
+    }
+}
+
+impl FilterEffect for FeDropShadow {
+    fn resolve(
+        &self,
+        _acquired_nodes: &mut AcquiredNodes<'_>,
+        node: &Node,
+    ) -> Result<Vec<ResolvedPrimitive>, FilterResolveError> {
+        let cascaded = CascadedValues::new_from_node(node);
+        let values = cascaded.get();
+
+        let color = resolve_color(
+            &values.flood_color().0,
+            values.flood_opacity().0,
+            values.color().0,
+        );
+
+        Ok(drop_shadow_primitives(
+            self.params.dx,
+            self.params.dy,
+            self.params.std_deviation,
+            color,
+        ))
+    }
+}
diff --git a/src/filters/mod.rs b/src/filters/mod.rs
index 8b0f37d5..e6f4724e 100644
--- a/src/filters/mod.rs
+++ b/src/filters/mod.rs
@@ -49,6 +49,7 @@ pub mod component_transfer;
 pub mod composite;
 pub mod convolve_matrix;
 pub mod displacement_map;
+pub mod drop_shadow;
 pub mod flood;
 pub mod gaussian_blur;
 pub mod image;
@@ -349,6 +350,10 @@ fn render_primitive(
 
     let bounds_builder = primitive.get_bounds(ctx);
 
+    // Note that feDropShadow is not handled here.  When its FilterElement::resolve() is called,
+    // it returns a series of lower-level primitives (flood, blur, offset, etc.) that make up
+    // the drop-shadow effect.
+
     match primitive.params {
         Blend(ref p)             => p.render(bounds_builder, ctx, acquired_nodes, draw_ctx),
         ColorMatrix(ref p)       => p.render(bounds_builder, ctx, acquired_nodes, draw_ctx),
diff --git a/tests/fixtures/reftests/svg2/bug743-fe-drop-shadow-ref.svg b/tests/fixtures/reftests/svg2/bug743-fe-drop-shadow-ref.svg
new file mode 100644
index 00000000..034f8b37
--- /dev/null
+++ b/tests/fixtures/reftests/svg2/bug743-fe-drop-shadow-ref.svg
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">
+  <filter id="drop-shadow" filterUnits="userSpaceOnUse">
+    <feGaussianBlur in="SourceAlpha" stdDeviation="5 10"/>
+    <feOffset dx="5" dy="10" result="offsetblur"/>
+    <feFlood flood-color="black" flood-opacity="0.5"/>
+    <feComposite in2="offsetblur" operator="in"/>
+    <feMerge>
+      <feMergeNode/>
+      <feMergeNode in="SourceGraphic"/>
+    </feMerge>    
+  </filter>
+
+  <rect x="0" y="0" width="100%" height="100%" fill="white"/>
+
+  <rect x="50" y="50" width="50" height="50" fill="blue" stroke="magenta" stroke-width="6" filter="url(#drop-shadow)"/>
+</svg>
diff --git a/tests/fixtures/reftests/svg2/bug743-fe-drop-shadow.svg b/tests/fixtures/reftests/svg2/bug743-fe-drop-shadow.svg
new file mode 100644
index 00000000..7054201f
--- /dev/null
+++ b/tests/fixtures/reftests/svg2/bug743-fe-drop-shadow.svg
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">
+  <filter id="drop-shadow" filterUnits="userSpaceOnUse">
+    <feDropShadow dx="5" dy="10" stdDeviation="5 10" flood-color="black" flood-opacity="0.5"/>
+  </filter>
+
+  <rect x="0" y="0" width="100%" height="100%" fill="white"/>
+
+  <rect x="50" y="50" width="50" height="50" fill="blue" stroke="magenta" stroke-width="6" filter="url(#drop-shadow)"/>
+</svg>
diff --git a/tests/src/filters.rs b/tests/src/filters.rs
index f756a781..9517e651 100644
--- a/tests/src/filters.rs
+++ b/tests/src/filters.rs
@@ -1,8 +1,8 @@
 use cairo;
 
 use crate::reference_utils::{Compare, Evaluate, Reference};
-use crate::test_compare_render_output;
 use crate::utils::{load_svg, render_document, SurfaceSize};
+use crate::{test_compare_render_output, test_svg_reference};
 
 #[test]
 fn invalid_filter_reference_cancels_filter_chain() {
@@ -363,3 +363,9 @@ test_compare_render_output!(
 </svg>
 "##,
 );
+
+test_svg_reference!(
+    bug_743_fe_drop_shadow,
+    "tests/fixtures/reftests/svg2/bug743-fe-drop-shadow.svg",
+    "tests/fixtures/reftests/svg2/bug743-fe-drop-shadow-ref.svg"
+);