LibWeb: Make SVG <path> tolerate relative first path coordinates

If the first element of an SVG path spec uses relative coordinates,
we'll now treat them as absolute. This is achieved by defaulting to
(0,0) as the initial "last point" in the path.

Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp

@@ -467,6 +467,9 @@ Gfx::Path& SVGPathElement::get_path()
     Gfx::Path path;
 
     for (auto& instruction : m_instructions) {
+        // If the first path element uses relative coordinates, we treat them as absolute by making them relative to (0, 0).
+        auto last_point = path.segments().is_empty() ? Gfx::FloatPoint { 0, 0 } : path.segments().last().point();
+
         auto& absolute = instruction.absolute;
         auto& data = instruction.data;
 
@@ -482,8 +485,7 @@ Gfx::Path& SVGPathElement::get_path()
             if (absolute) {
                 path.move_to(point);
             } else {
-                VERIFY(!path.segments().is_empty());
-                path.move_to(point + path.segments().last().point());
+                path.move_to(point + last_point);
             }
             break;
         }
@@ -495,29 +497,22 @@ Gfx::Path& SVGPathElement::get_path()
             if (absolute) {
                 path.line_to(point);
             } else {
-                VERIFY(!path.segments().is_empty());
-                path.line_to(point + path.segments().last().point());
+                path.line_to(point + last_point);
             }
             break;
         }
         case PathInstructionType::HorizontalLine: {
-            VERIFY(!path.segments().is_empty());
-            auto last_point = path.segments().last().point();
-            if (absolute) {
+            if (absolute)
                 path.line_to(Gfx::FloatPoint { data[0], last_point.y() });
-            } else {
+            else
                 path.line_to(Gfx::FloatPoint { data[0] + last_point.x(), last_point.y() });
-            }
             break;
         }
         case PathInstructionType::VerticalLine: {
-            VERIFY(!path.segments().is_empty());
-            auto last_point = path.segments().last().point();
-            if (absolute) {
+            if (absolute)
                 path.line_to(Gfx::FloatPoint { last_point.x(), data[0] });
-            } else {
+            else
                 path.line_to(Gfx::FloatPoint { last_point.x(), data[0] + last_point.y() });
-            }
             break;
         }
         case PathInstructionType::EllipticalArc: {
@@ -526,18 +521,15 @@ Gfx::Path& SVGPathElement::get_path()
             double x_axis_rotation = double { data[2] } * M_DEG2RAD;
             double large_arc_flag = data[3];
             double sweep_flag = data[4];
-            auto& last_point = path.segments().last().point();
 
             Gfx::FloatPoint next_point;
 
-            if (absolute) {
+            if (absolute)
                 next_point = { data[5], data[6] };
-            } else {
+            else
                 next_point = { data[5] + last_point.x(), data[6] + last_point.y() };
-            }
 
             path.elliptical_arc_to(next_point, { rx, ry }, x_axis_rotation, large_arc_flag != 0, sweep_flag != 0);
-
             break;
         }
         case PathInstructionType::QuadraticBezierCurve: {
@@ -550,8 +542,6 @@ Gfx::Path& SVGPathElement::get_path()
                 path.quadratic_bezier_curve_to(through, point);
                 m_previous_control_point = through;
             } else {
-                VERIFY(!path.segments().is_empty());
-                auto last_point = path.segments().last().point();
                 auto control_point = through + last_point;
                 path.quadratic_bezier_curve_to(control_point, point + last_point);
                 m_previous_control_point = control_point;
@@ -561,9 +551,6 @@ Gfx::Path& SVGPathElement::get_path()
         case PathInstructionType::SmoothQuadraticBezierCurve: {
             clear_last_control_point = false;
 
-            VERIFY(!path.segments().is_empty());
-            auto last_point = path.segments().last().point();
-
             if (m_previous_control_point.is_null()) {
                 m_previous_control_point = last_point;
             }
@@ -589,9 +576,9 @@ Gfx::Path& SVGPathElement::get_path()
             Gfx::FloatPoint c2 = { data[2], data[3] };
             Gfx::FloatPoint p2 = { data[4], data[5] };
             if (!absolute) {
-                p2 += path.segments().last().point();
-                c1 += path.segments().last().point();
-                c2 += path.segments().last().point();
+                p2 += last_point;
+                c1 += last_point;
+                c2 += last_point;
             }
             path.cubic_bezier_curve_to(c1, c2, p2);
             break;