LibGfx+LibWeb: Wire up CanvasRenderingContext2D.ellipse()

Note that this is *extremely* naive, and not very good at being correct.

Userland/Libraries/LibGfx/Painter.cpp

@@ -1492,7 +1492,7 @@ void Painter::for_each_line_segment_on_bezier_curve(const FloatPoint& control_po
 
 static bool can_approximate_elliptical_arc(const FloatPoint& p1, const FloatPoint& p2, const FloatPoint& center, const FloatPoint radii, float x_axis_rotation, float theta_1, float theta_delta)
 {
-    constexpr static float tolerance = 0.5f;
+    constexpr static float tolerance = 0.3f;
 
     auto half_theta_delta = theta_delta / 2.0f;
 

Userland/Libraries/LibGfx/Path.cpp

@@ -30,11 +30,14 @@
 #include <AK/StringBuilder.h>
 #include <LibGfx/Painter.h>
 #include <LibGfx/Path.h>
+#include <math.h>
 
 namespace Gfx {
 
-void Path::elliptical_arc_to(const FloatPoint& next_point, const FloatPoint& radii, double x_axis_rotation, bool large_arc, bool sweep)
+void Path::elliptical_arc_to(const FloatPoint& point, const FloatPoint& radii, double x_axis_rotation, bool large_arc, bool sweep)
 {
+    auto next_point = point;
+
     double rx = radii.x();
     double ry = radii.y();
 
@@ -58,6 +61,18 @@ void Path::elliptical_arc_to(const FloatPoint& next_point, const FloatPoint& rad
     if (ry < 0)
         ry *= -1.0;
 
+    // POSSIBLY HACK: Handle the case where both points are the same.
+    auto same_endpoints = next_point == last_point;
+    if (same_endpoints) {
+        if (!large_arc) {
+            // Nothing is going to be drawn anyway.
+            return;
+        }
+
+        // Move the endpoint by a small amount to avoid division by zero.
+        next_point.move_by(0.01f, 0.01f);
+    }
+
     // Find (cx, cy), theta_1, theta_delta
     // Step 1: Compute (x1', y1')
     auto x_avg = (last_point.x() - next_point.x()) / 2.0f;
@@ -104,20 +119,18 @@ void Path::elliptical_arc_to(const FloatPoint& next_point, const FloatPoint& rad
     auto theta_delta = theta_2 - theta_1;
 
     if (!sweep && theta_delta > 0.0f) {
-        theta_delta -= M_TAU;
+        theta_delta -= 2 * M_PI;
     } else if (sweep && theta_delta < 0) {
-        theta_delta += M_TAU;
+        theta_delta += 2 * M_PI;
     }
 
-    append_segment<EllipticalArcSegment>(
+    elliptical_arc_to(
         next_point,
-        FloatPoint(cx, cy),
-        FloatPoint(rx, ry),
-        static_cast<float>(x_axis_rotation),
-        static_cast<float>(theta_1),
-        static_cast<float>(theta_delta));
-
-    invalidate_split_lines();
+        { cx, cy },
+        { rx, ry },
+        x_axis_rotation,
+        theta_1,
+        theta_delta);
 }
 
 void Path::close()

Userland/Libraries/LibGfx/Path.h

@@ -160,6 +160,20 @@ public:
         elliptical_arc_to(point, { radius, radius }, 0, large_arc, sweep);
     }
 
+    // Note: This does not do any sanity checks!
+    void elliptical_arc_to(const FloatPoint& endpoint, const FloatPoint& center, const FloatPoint& radii, double x_axis_rotation, double theta, double theta_delta)
+    {
+        append_segment<EllipticalArcSegment>(
+            endpoint,
+            center,
+            radii,
+            x_axis_rotation,
+            theta,
+            theta_delta);
+
+        invalidate_split_lines();
+    }
+
     void close();
     void close_all_subpaths();