Fix bounding box computation for lines in curves (typst#6647)

Co-authored-by: Laurenz <[email protected]>

Author: saecki

crates/typst-library/src/visualize/curve.rs

@@ -476,26 +476,18 @@ impl Curve {
 
     /// Computes the size of the bounding box of this curve.
     pub fn bbox_size(&self) -> Size {
-        let mut min_x = Abs::inf();
-        let mut min_y = Abs::inf();
-        let mut max_x = -Abs::inf();
-        let mut max_y = -Abs::inf();
+        let mut min = Point::splat(Abs::inf());
+        let mut max = Point::splat(-Abs::inf());
 
         let mut cursor = Point::zero();
         for item in self.0.iter() {
             match item {
                 CurveItem::Move(to) => {
-                    min_x = min_x.min(cursor.x);
-                    min_y = min_y.min(cursor.y);
-                    max_x = max_x.max(cursor.x);
-                    max_y = max_y.max(cursor.y);
                     cursor = *to;
                 }
                 CurveItem::Line(to) => {
-                    min_x = min_x.min(cursor.x);
-                    min_y = min_y.min(cursor.y);
-                    max_x = max_x.max(cursor.x);
-                    max_y = max_y.max(cursor.y);
+                    min = min.min(cursor).min(*to);
+                    max = max.max(cursor).max(*to);
                     cursor = *to;
                 }
                 CurveItem::Cubic(c0, c1, end) => {
@@ -507,17 +499,17 @@ impl Curve {
                     );
 
                     let bbox = cubic.bounding_box();
-                    min_x = min_x.min(Abs::pt(bbox.x0)).min(Abs::pt(bbox.x1));
-                    min_y = min_y.min(Abs::pt(bbox.y0)).min(Abs::pt(bbox.y1));
-                    max_x = max_x.max(Abs::pt(bbox.x0)).max(Abs::pt(bbox.x1));
-                    max_y = max_y.max(Abs::pt(bbox.y0)).max(Abs::pt(bbox.y1));
+                    min.x = min.x.min(Abs::pt(bbox.x0)).min(Abs::pt(bbox.x1));
+                    min.y = min.y.min(Abs::pt(bbox.y0)).min(Abs::pt(bbox.y1));
+                    max.x = max.x.max(Abs::pt(bbox.x0)).max(Abs::pt(bbox.x1));
+                    max.y = max.y.max(Abs::pt(bbox.y0)).max(Abs::pt(bbox.y1));
                     cursor = *end;
                 }
                 CurveItem::Close => (),
             }
         }
 
-        Size::new(max_x - min_x, max_y - min_y)
+        Size::new(max.x - min.x, max.y - min.y)
     }
 }
 

tests/ref/curve-stroke-gradient-sharp.png

@@ -130,6 +130,16 @@
   down, up, down, up, down,
 )
 
+--- curve-stroke-gradient-sharp ---
+#set page(width: auto)
+#let down = curve.line((40pt, 40pt), relative: true)
+#let up = curve.line((40pt, -40pt), relative: true)
+
+#curve(
+  stroke: 4pt + gradient.linear(red, blue).sharp(3),
+  down, up, down, up, down,
+)
+
 --- curve-fill-rule ---
 #stack(
   dir: ltr,