usvg/parser: fix width/height computation when only one is specified

In case only one of the height/width attributes are set and we have a
viewBox, we currently report an incorrect size: the height/width that is
set and 100% of the viewbox's attribute for the other attribute.

This is incorrect, and we should instead compute the missing attribute
value from the specified one and the viewBox' aspect ratio, like was
done by #715.

I have validated that this fixes servo's
   servo/servo#41273

Signed-off-by: Simon Martin <simon@nasilyan.com>

Author: simartin

crates/usvg/src/parser/converter.rs

@@ -540,7 +540,18 @@ fn resolve_svg_size(svg: &SvgNode, opt: &Options) -> (Result<Size, Error>, bool)
             svg.convert_user_length(AId::Height, &state, def)
         };
 
-        Size::from_wh(w, h)
+        // If only one of height/width is not specified, its value should be
+        // computed from the other and the viewbox' aspect ratio.
+        match (svg.attribute::<Length>(AId::Width), svg.attribute::<Length>(AId::Height)) {
+            (Some(_), None) => {
+                Size::from_wh(w, vbox.height() * w / vbox.width())
+            },
+            (None, Some(_)) => {
+                Size::from_wh(vbox.width() * h / vbox.height(), h)
+            },
+            (_, _) => Size::from_wh(w, h),
+        }
+
     } else {
         Size::from_wh(
             svg.convert_user_length(AId::Width, &state, def),

crates/usvg/tests/parser.rs

@@ -217,6 +217,38 @@ fn size_detection_5() {
     assert_eq!(tree.size(), usvg::Size::from_wh(100.0, 100.0).unwrap());
 }
 
+#[test]
+fn size_detection_6() {
+    let svg =
+        "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 10' width='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(30.0, 30.0).unwrap());
+}
+
+#[test]
+fn size_detection_7() {
+    let svg =
+        "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 20' width='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(30.0, 60.0).unwrap());
+}
+
+#[test]
+fn size_detection_8() {
+    let svg =
+        "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 10' height='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(30.0, 30.0).unwrap());
+}
+
+#[test]
+fn size_detection_9() {
+    let svg =
+        "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 20' height='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(15.0, 30.0).unwrap());
+}
+
 #[test]
 fn invalid_size_1() {
     let svg = "<svg width='0' height='0' viewBox='0 0 10 20' xmlns='http://www.w3.org/2000/svg'/>";