Add support for stylesheet injection (#785)

Closes  #277

Author: LaurenzV

crates/resvg/src/main.rs

@@ -144,6 +144,8 @@ OPTIONS:
                                 [default: 96] [possible values: 10..4000 (inclusive)]
   --background COLOR            Sets the background color
                                 Examples: red, #fff, #fff000
+  --stylesheet PATH             Inject a stylesheet that should be used when resolving
+                                CSS attributes.
 
   --languages LANG              Sets a comma-separated list of languages that
                                 will be used during the 'systemLanguage'
@@ -238,6 +240,7 @@ struct CliArgs {
     font_dirs: Vec<path::PathBuf>,
     skip_system_fonts: bool,
     list_fonts: bool,
+    style_sheet: Option<path::PathBuf>,
 
     query_all: bool,
     export_id: Option<String>,
@@ -307,6 +310,7 @@ fn collect_args() -> Result<CliArgs, pico_args::Error> {
         export_area_page: input.contains("--export-area-page"),
 
         export_area_drawing: input.contains("--export-area-drawing"),
+        style_sheet: input.opt_value_from_str("--stylesheet").unwrap_or_default(),
 
         perf: input.contains("--perf"),
         quiet: input.contains("--quiet"),
@@ -548,6 +552,16 @@ fn parse_args() -> Result<Args, String> {
         }
     };
 
+    let style_sheet = match args.style_sheet.as_ref() {
+        Some(p) => Some(
+            std::fs::read(&p)
+                .ok()
+                .and_then(|s| std::str::from_utf8(&s).ok().map(|s| s.to_string()))
+                .ok_or("failed to read stylesheet".to_string())?,
+        ),
+        None => None,
+    };
+
     let usvg = usvg::Options {
         resources_dir,
         dpi: args.dpi as f32,
@@ -564,6 +578,7 @@ fn parse_args() -> Result<Args, String> {
         image_href_resolver: usvg::ImageHrefResolver::default(),
         font_resolver: usvg::FontResolver::default(),
         fontdb: Arc::new(fontdb::Database::new()),
+        style_sheet,
     };
 
     Ok(Args {

crates/usvg/src/main.rs

@@ -26,6 +26,8 @@ OPTIONS:
 
   --dpi DPI                         Sets the resolution
                                     [default: 96] [possible values: 10..4000 (inclusive)]
+  --stylesheet PATH                 Inject a stylesheet that should be used when resolving
+                                    CSS attributes.
   --languages LANG                  Sets a comma-separated list of languages that
                                     will be used during the 'systemLanguage'
                                     attribute resolving
@@ -137,6 +139,7 @@ struct Args {
     attrs_indent: xmlwriter::Indent,
     coordinates_precision: Option<u8>,
     transforms_precision: Option<u8>,
+    style_sheet: Option<PathBuf>,
 
     quiet: bool,
 
@@ -206,6 +209,7 @@ fn collect_args() -> Result<Args, pico_args::Error> {
         coordinates_precision: input
             .opt_value_from_fn("--coordinates-precision", parse_precision)?,
         transforms_precision: input.opt_value_from_fn("--transforms-precision", parse_precision)?,
+        style_sheet: input.opt_value_from_str("--stylesheet").unwrap_or_default(),
 
         quiet: input.contains("--quiet"),
 
@@ -400,6 +404,16 @@ fn process(args: Args) -> Result<(), String> {
         }
     };
 
+    let style_sheet = match args.style_sheet.as_ref() {
+        Some(p) => Some(
+            std::fs::read(&p)
+                .ok()
+                .and_then(|s| std::str::from_utf8(&s).ok().map(|s| s.to_string()))
+                .ok_or("failed to read stylesheet".to_string())?,
+        ),
+        None => None,
+    };
+
     let re_opt = usvg::Options {
         resources_dir,
         dpi: args.dpi as f32,
@@ -418,6 +432,7 @@ fn process(args: Args) -> Result<(), String> {
         image_href_resolver: usvg::ImageHrefResolver::default(),
         font_resolver: usvg::FontResolver::default(),
         fontdb: Arc::new(fontdb),
+        style_sheet,
     };
 
     let input_svg = match in_svg {

crates/usvg/src/parser/mod.rs

@@ -121,7 +121,7 @@ impl crate::Tree {
 
     /// Parses `Tree` from `roxmltree::Document`.
     pub fn from_xmltree(doc: &roxmltree::Document, opt: &Options) -> Result<Self, Error> {
-        let doc = svgtree::Document::parse_tree(doc)?;
+        let doc = svgtree::Document::parse_tree(doc, opt.style_sheet.as_deref())?;
         self::converter::convert_doc(&doc, opt)
     }
 }

crates/usvg/src/parser/options.rs

@@ -96,6 +96,9 @@ pub struct Options<'a> {
     /// be the same as this one.
     #[cfg(feature = "text")]
     pub fontdb: Arc<fontdb::Database>,
+    /// A CSS stylesheet that should be injected into the SVG. Can be used to overwrite
+    /// certain attributes.
+    pub style_sheet: Option<String>,
 }
 
 impl Default for Options<'_> {
@@ -116,6 +119,7 @@ impl Default for Options<'_> {
             font_resolver: FontResolver::default(),
             #[cfg(feature = "text")]
             fontdb: Arc::new(fontdb::Database::new()),
+            style_sheet: None,
         }
     }
 }

crates/usvg/src/parser/svgtree/parse.rs

@@ -16,8 +16,11 @@ const XML_NAMESPACE_NS: &str = "http://www.w3.org/XML/1998/namespace";
 
 impl<'input> Document<'input> {
     /// Parses a [`Document`] from a [`roxmltree::Document`].
-    pub fn parse_tree(xml: &roxmltree::Document<'input>) -> Result<Document<'input>, Error> {
-        parse(xml)
+    pub fn parse_tree(
+        xml: &roxmltree::Document<'input>,
+        injected_stylesheet: Option<&'input str>,
+    ) -> Result<Document<'input>, Error> {
+        parse(xml, injected_stylesheet)
     }
 
     pub(crate) fn append(&mut self, parent_id: NodeId, kind: NodeKind) -> NodeId {
@@ -51,7 +54,10 @@ impl<'input> Document<'input> {
     }
 }
 
-fn parse<'input>(xml: &roxmltree::Document<'input>) -> Result<Document<'input>, Error> {
+fn parse<'input>(
+    xml: &roxmltree::Document<'input>,
+    injected_stylesheet: Option<&'input str>,
+) -> Result<Document<'input>, Error> {
     let mut doc = Document {
         nodes: Vec::new(),
         attrs: Vec::new(),
@@ -76,7 +82,7 @@ fn parse<'input>(xml: &roxmltree::Document<'input>) -> Result<Document<'input>,
         kind: NodeKind::Root,
     });
 
-    let style_sheet = resolve_css(xml);
+    let style_sheet = resolve_css(xml, injected_stylesheet);
 
     parse_xml_node_children(
         xml.root(),
@@ -565,9 +571,18 @@ fn parse_svg_use_element<'input>(
     )
 }
 
-fn resolve_css<'a>(xml: &'a roxmltree::Document<'a>) -> simplecss::StyleSheet<'a> {
+fn resolve_css<'a>(
+    xml: &'a roxmltree::Document<'a>,
+    style_sheet: Option<&'a str>,
+) -> simplecss::StyleSheet<'a> {
     let mut sheet = simplecss::StyleSheet::new();
 
+    // Injected style sheets do not override internal ones (we mimic the logic of rsvg-convert),
+    // so we need to parse it first.
+    if let Some(style_sheet) = style_sheet {
+        sheet.parse_more(style_sheet);
+    }
+
     for node in xml.descendants().filter(|n| n.has_tag_name("style")) {
         match node.attribute("type") {
             Some("text/css") => {}

crates/usvg/tests/parser.rs

@@ -1,3 +1,5 @@
+use usvg::Color;
+
 #[test]
 fn clippath_with_invalid_child() {
     let svg = "
@@ -14,6 +16,65 @@ fn clippath_with_invalid_child() {
     assert_eq!(tree.root().has_children(), false);
 }
 
+#[test]
+fn stylesheet_injection() {
+    let svg = "<svg id='svg1' viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'>
+    <style>
+        #rect4 {
+            fill: green
+        }
+    </style>
+    <rect id='rect1' x='20' y='20' width='60' height='60'/>
+    <rect id='rect2' x='120' y='20' width='60' height='60' fill='green'/>
+    <rect id='rect3' x='20' y='120' width='60' height='60' style='fill: green'/>
+    <rect id='rect4' x='120' y='120' width='60' height='60'/>
+</svg>
+";
+
+    let stylesheet = "rect { fill: red }".to_string();
+
+    let options = usvg::Options {
+        style_sheet: Some(stylesheet),
+        ..usvg::Options::default()
+    };
+
+    let tree = usvg::Tree::from_str(&svg, &options).unwrap();
+
+    let usvg::Node::Path(ref first) = &tree.root().children()[0] else {
+        unreachable!()
+    };
+
+    // Only the rects with no CSS attributes should be overridden.
+    assert_eq!(
+        first.fill().unwrap().paint(),
+        &usvg::Paint::Color(Color::new_rgb(255, 0, 0))
+    );
+
+    let usvg::Node::Path(ref second) = &tree.root().children()[1] else {
+        unreachable!()
+    };
+    assert_eq!(
+        second.fill().unwrap().paint(),
+        &usvg::Paint::Color(Color::new_rgb(255, 0, 0))
+    );
+
+    let usvg::Node::Path(ref third) = &tree.root().children()[2] else {
+        unreachable!()
+    };
+    assert_eq!(
+        third.fill().unwrap().paint(),
+        &usvg::Paint::Color(Color::new_rgb(0, 128, 0))
+    );
+
+    let usvg::Node::Path(ref third) = &tree.root().children()[3] else {
+        unreachable!()
+    };
+    assert_eq!(
+        third.fill().unwrap().paint(),
+        &usvg::Paint::Color(Color::new_rgb(0, 128, 0))
+    );
+}
+
 #[test]
 fn simplify_paths() {
     let svg = "