From 8da21583db9d9322e898d73f13711f1938ebaa8d Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 27 Sep 2021 18:29:10 +0200
Subject: [PATCH] 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.
---
 .../Libraries/LibWeb/SVG/SVGPathElement.cpp   | 41 +++++++------------
 1 file changed, 14 insertions(+), 27 deletions(-)

diff --git a/Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp
index e5a2c5e3c9..741df4a6b6 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp
+++ b/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;