Fix alignment of gradients and patterns on strokes in PNG (#4634)

crates/typst-render/src/paint.rs

@@ -185,6 +185,12 @@ pub fn to_sk_paint<'a>(
                     .container_transform
                     .post_concat(state.transform.invert().unwrap()),
             };
+
+            let gradient_map = match relative {
+                RelativeTo::Self_ => gradient_map,
+                RelativeTo::Parent => None,
+            };
+
             let width =
                 (container_size.x.to_f32().abs() * state.pixel_per_pt).ceil() as u32;
             let height =
@@ -225,6 +231,13 @@ pub fn to_sk_paint<'a>(
             let canvas = render_pattern_frame(&state, pattern);
             *pixmap = Some(Arc::new(canvas));
 
+            let offset = match relative {
+                RelativeTo::Self_ => {
+                    gradient_map.map(|(offset, _)| -offset).unwrap_or_default()
+                }
+                RelativeTo::Parent => Point::zero(),
+            };
+
             // Create the shader
             sk_paint.shader = sk::Pattern::new(
                 pixmap.as_ref().unwrap().as_ref().as_ref(),
@@ -232,7 +245,8 @@ pub fn to_sk_paint<'a>(
                 sk::FilterQuality::Nearest,
                 1.0,
                 fill_transform
-                    .pre_scale(1.0 / state.pixel_per_pt, 1.0 / state.pixel_per_pt),
+                    .pre_scale(1.0 / state.pixel_per_pt, 1.0 / state.pixel_per_pt)
+                    .pre_translate(offset.x.to_f32(), offset.y.to_f32()),
             );
         }
     }

tests/suite/visualize/gradient.typ

@@ -175,6 +175,22 @@
   )
 )
 
+--- gradient-linear-stroke-relative-parent ---
+// The image should look as if there is a single gradient that is being used for
+// both the circle stroke and the block fill.
+#align(
+  center + horizon,
+  block(
+    width: 50pt,
+    height: 50pt,
+    fill: gradient.linear(red, blue).sharp(4),
+    circle(
+      radius: 18pt,
+      stroke: 5pt + gradient.linear(red, blue, relative: "parent").sharp(4),
+    )
+  )
+)
+
 --- gradient-linear-line ---
 // Test gradient on lines
 #set page(width: 100pt, height: 100pt)

tests/suite/visualize/pattern.typ

@@ -101,13 +101,35 @@
   center + top,
   square(
     size: 50pt,
-    stroke: 5pt + pattern(
+    fill: pattern(
       size: (5pt, 5pt),
       align(horizon + center, circle(fill: blue, radius: 2.5pt))
+    ),
+    stroke: 7.5pt + pattern(
+      size: (5pt, 5pt),
+      align(horizon + center, circle(fill: red, radius: 2.5pt))
     )
   )
 )
 
+--- pattern-stroke-relative-parent ---
+// Test pattern on strokes with relative set to `"parent"`
+// The pattern on the circle should align with the pattern on the square.
+#align(
+  center + top,
+  block(
+    width: 50pt,
+    height: 50pt,
+    fill: pattern(size: (5pt, 5pt), circle(radius: 2.5pt, fill: blue)),
+    align(center + horizon, circle(
+      radius: 15pt,
+      stroke: 7.5pt + pattern(
+        size: (5pt, 5pt), circle(radius: 2.5pt, fill: red), relative: "parent"
+      ),
+    ))
+  )
+)
+
 --- pattern-text ---
 // Test a pattern on some text
 // You shouldn't be able to see the text, if you can then