SVGLoader: adding support for elliptical arc

examples/js/loaders/SVGLoader.js

@@ -221,14 +221,13 @@ THREE.SVGLoader.prototype = {
 						break;
 
 					case 'A':
-						console.warn( command );
 						var numbers = parseFloats( data );
 						for ( var j = 0, jl = numbers.length; j < jl; j += 7 ) {
-							// TODO
-							point.x = numbers[ j + 5 ];
-							point.y = numbers[ j + 6 ];
-							control.x = point.x;
-							control.y = point.y;
+
+							var radius = { x: numbers[ j ], y: numbers[ j + 1 ] };
+							var end = { x: numbers[ j + 5 ], y: numbers[ j + 6 ] };
+							svgEllipsisToThreeEllipsis( path, control, radius, numbers[ j + 2 ], numbers[ j + 3 ], numbers[ j + 4 ], end );
+
 						}
 						break;
 
@@ -372,6 +371,53 @@ THREE.SVGLoader.prototype = {
 
 		}
 
+
+		/**
+		 * https://www.w3.org/TR/SVG/implnote.html#ArcImplementationNotes
+		 * https://mortoray.com/2017/02/16/rendering-an-svg-elliptical-arc-as-bezier-curves/ Appendix: Endpoint to center arc conversion
+		 * From
+		 * rx ry x-axis-rotation large-arc-flag sweep-flag x y
+		 * To
+		 * aX, aY, xRadius, yRadius, aStartAngle, aEndAngle, aClockwise, aRotation
+		 */
+		function svgEllipsisToThreeEllipsis( path, start, radius, x_axis_rotation, large_arc_flag, sweep_flag, end ) {
+
+			//F.6.6 Correction of out-of-range radii
+			//Step 2: Ensure radii are positive
+			var rX = Math.abs( radius.x );
+			var rY = Math.abs( radius.y );
+			//Step 3: Ensure radii are large enough looks like over engineering
+
+			// Step 1: Compute (x1′, y1′)
+			var midDist = new THREE.Vector2().subVectors( start, end ).multiplyScalar( 0.5 );
+			var x1p = Math.cos( x_axis_rotation ) * midDist.x + Math.sin( x_axis_rotation ) * midDist.y;
+			var y1p = - Math.sin( x_axis_rotation ) * midDist.x + Math.cos( x_axis_rotation ) * midDist.y;
+
+			// Step 2: Compute (cx′, cy′)
+			var rxs = rX * rX;
+			var rys = rY * rY;
+			var x1ps = x1p * x1p;
+			var y1ps = y1p * y1p;
+			var dq = ( rxs * y1ps + rys * x1ps );
+			var pq = ( rxs * rys - dq ) / dq;
+			var q = Math.sqrt( pq );
+			if ( large_arc_flag === sweep_flag ) q = - q;
+			var cxp = q * rX * y1p / rY;
+			var cyp = - q * rY * x1p / rX;
+
+			// Step 3: Compute (cx, cy) from (cx′, cy′)
+			var cx = Math.cos( x_axis_rotation ) * cxp - Math.sin( x_axis_rotation ) * cyp + ( start.x + end.x ) / 2;
+			var cy = Math.sin( x_axis_rotation ) * cxp + Math.cos( x_axis_rotation ) * cyp + ( start.y + end.y ) / 2;
+
+			// Step 4: Compute θ1 and Δθ
+			var startAngle = new THREE.Vector2( ( x1p - cxp ) / rX, ( y1p - cyp ) / rY ).angle();
+			var endAngle = new THREE.Vector2( ( - x1p - cxp ) / rX, ( - y1p - cyp ) / rY ).angle();
+			if ( ! sweep_flag ) endAngle -= 2 * Math.PI;
+
+			path.currentPath.absellipse( cx, cy, rX, rY, startAngle, endAngle, endAngle > startAngle, x_axis_rotation );
+
+		}
+
 		/*
 		* According to https://www.w3.org/TR/SVG/shapes.html#RectElementRXAttribute
 		* rounded corner should be rendered to elliptical arc, but bezier curve does the job well enough
@@ -586,4 +632,4 @@ THREE.SVGLoader.prototype = {
 
 	}
 
-};
+};