LibWeb: Implement Path2D#addPath

Required by Ruffle.

Userland/Libraries/LibWeb/HTML/Path2D.cpp

@@ -1,11 +1,13 @@
 /*
  * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
  * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2023, Luke Wilde <lukew@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/Geometry/DOMMatrix.h>
 #include <LibWeb/HTML/Path2D.h>
 #include <LibWeb/SVG/AttributeParser.h>
 #include <LibWeb/SVG/SVGPathElement.h>
@@ -62,4 +64,37 @@ JS::ThrowCompletionOr<void> Path2D::initialize(JS::Realm& realm)
     return {};
 }
 
+// https://html.spec.whatwg.org/multipage/canvas.html#dom-path2d-addpath
+WebIDL::ExceptionOr<void> Path2D::add_path(JS::NonnullGCPtr<Path2D> path, Geometry::DOMMatrix2DInit& transform)
+{
+    // The addPath(path, transform) method, when invoked on a Path2D object a, must run these steps:
+
+    // 1. If the Path2D object path has no subpaths, then return.
+    if (path->path().segments().is_empty())
+        return {};
+
+    // 2. Let matrix be the result of creating a DOMMatrix from the 2D dictionary transform.
+    auto matrix = TRY(Geometry::DOMMatrix::create_from_dom_matrix_2d_init(realm(), transform));
+
+    // 3. If one or more of matrix's m11 element, m12 element, m21 element, m22 element, m41 element, or m42 element are infinite or NaN, then return.
+    if (!isfinite(matrix->m11()) || !isfinite(matrix->m12()) || !isfinite(matrix->m21()) || !isfinite(matrix->m22()) || !isfinite(matrix->m41()) || !isfinite(matrix->m42()))
+        return {};
+
+    // 4. Create a copy of all the subpaths in path. Let this copy be known as c.
+    // 5. Transform all the coordinates and lines in c by the transform matrix matrix.
+    auto copy = path->path().copy_transformed(Gfx::AffineTransform { static_cast<float>(matrix->m11()), static_cast<float>(matrix->m12()), static_cast<float>(matrix->m21()), static_cast<float>(matrix->m22()), static_cast<float>(matrix->m41()), static_cast<float>(matrix->m42()) });
+
+    // 6. Let (x, y) be the last point in the last subpath of c.
+    auto xy = copy.segments().last().point();
+
+    // 7. Add all the subpaths in c to a.
+    // FIXME: Is this correct?
+    this->path().add_path(copy);
+
+    // 8. Create a new subpath in a with (x, y) as the only point in the subpath.
+    this->move_to(xy.x(), xy.y());
+
+    return {};
+}
+
 }

Userland/Libraries/LibWeb/HTML/Path2D.h

@@ -9,6 +9,7 @@
 #include <AK/RefCounted.h>
 #include <LibGfx/Path.h>
 #include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/Geometry/DOMMatrixReadOnly.h>
 #include <LibWeb/HTML/Canvas/CanvasPath.h>
 
 namespace Web::HTML {
@@ -25,6 +26,8 @@ public:
 
     virtual ~Path2D() override;
 
+    WebIDL::ExceptionOr<void> add_path(JS::NonnullGCPtr<Path2D> path, Geometry::DOMMatrix2DInit& transform);
+
 private:
     Path2D(JS::Realm&, Optional<Variant<JS::Handle<Path2D>, DeprecatedString>> const&);
 

Userland/Libraries/LibWeb/HTML/Path2D.idl

@@ -1,3 +1,4 @@
+#import <Geometry/DOMMatrixReadOnly.idl>
 #import <HTML/Canvas/CanvasPath.idl>
 
 // https://html.spec.whatwg.org/multipage/canvas.html#path2d
@@ -5,7 +6,7 @@
 interface Path2D {
     constructor(optional (Path2D or DOMString) path);
 
-    // FIXME: undefined addPath(Path2D path, optional DOMMatrix2DInit transform = {});
+    undefined addPath(Path2D path, optional DOMMatrix2DInit transform = {});
 };
 
 Path2D includes CanvasPath;