🐛 improve curved line on EBNF diagram

plantuml#2075

src/net/sourceforge/plantuml/ebnf/ETileOptional.java

@@ -49,6 +49,7 @@
 import net.sourceforge.plantuml.style.ISkinParam;
 import net.sourceforge.plantuml.style.SName;
 
+@Deprecated()
 public class ETileOptional extends ETile {
 
 	private final double deltax;

src/net/sourceforge/plantuml/ebnf/ETileOptional2.java

@@ -51,7 +51,7 @@
 
 public class ETileOptional2 extends ETile {
 
-	private final double deltax = 25;
+	private final double deltax = 24;
 	private final double deltay = 20;
 	private final ETile orig;
 	private final ISkinParam skinParam;
@@ -96,19 +96,12 @@ public void drawU(UGraphic ug) {
 		final double linePos = getH1(stringBounder);
 
 		drawHlineDirected(ug, linePos, 0, dim.getWidth(), 0.4, 25);
-		final double corner = 12;
+		final double corner = 12; // deltax/2
 
-		CornerCurved.createNE(corner).drawU(ug.apply(new UTranslate(corner, linePos)));
-		CornerCurved.createSW(corner)
-				.drawU(ug.apply(new UTranslate(corner, getDeltaY(stringBounder) + orig.getH1(stringBounder))));
-		drawVline(ug, corner, linePos + corner, getDeltaY(stringBounder) + orig.getH1(stringBounder) - corner);
+		final Zigzag zigzag = new Zigzag(9, 2 * corner, getDeltaY(stringBounder) + orig.getH1(stringBounder) - linePos);
 
-		final double posB = dim.getWidth() - corner;
-
-		CornerCurved.createNW(corner).drawU(ug.apply(new UTranslate(posB, linePos)));
-		CornerCurved.createSE(corner)
-				.drawU(ug.apply(new UTranslate(posB, getDeltaY(stringBounder) + orig.getH1(stringBounder))));
-		drawVline(ug, posB, linePos + corner, getDeltaY(stringBounder) + orig.getH1(stringBounder) - corner);
+		ug.apply(new UTranslate(0, linePos)).draw(zigzag.pathDown());
+		ug.apply(new UTranslate(dim.getWidth() - 2 * corner, linePos)).draw(zigzag.pathUp());
 
 		orig.drawU(ug.apply(new UTranslate(deltax, getDeltaY(stringBounder))));
 

src/net/sourceforge/plantuml/klimt/Zigzag.java

@@ -0,0 +1,96 @@
+/* ========================================================================
+ * PlantUML : a free UML diagram generator
+ * ========================================================================
+ *
+ * (C) Copyright 2009-2020, Arnaud Roques
+ *
+ * Project Info:  https://plantuml.com
+ * 
+ * If you like this project or if you find it useful, you can support us at:
+ * 
+ * https://plantuml.com/patreon (only 1$ per month!)
+ * https://plantuml.com/paypal
+ * 
+ * This file is part of PlantUML.
+ *
+ * PlantUML is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PlantUML distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ *
+ *
+ * Original Author:  Arnaud Roques
+ *
+ *
+ */
+package net.sourceforge.plantuml.ebnf;
+
+import net.sourceforge.plantuml.klimt.UPath;
+
+public class Zigzag {
+
+	private final double width;
+	private final double height;
+	private final double ctrl;
+
+	public Zigzag(double ctrl, double width, double height) {
+		this.ctrl = ctrl;
+		this.width = width;
+		this.height = height;
+	}
+
+	public UPath pathDown() {
+		final UPath path = UPath.none();
+		final double xm = width / 2;
+		final double ym = height / 2;
+
+		path.moveTo(0, 0);
+
+		final double cp1x1 = ctrl;
+		final double cp1y1 = 0;
+		final double cp1x2 = xm;
+		final double cp1y2 = ym - ctrl;
+		path.cubicTo(cp1x1, cp1y1, cp1x2, cp1y2, xm, ym);
+
+		final double cp2x1 = xm;
+		final double cp2y1 = ym + ctrl;
+		final double cp2x2 = width - ctrl;
+		final double cp2y2 = height;
+		path.cubicTo(cp2x1, cp2y1, cp2x2, cp2y2, width, height);
+
+		return path;
+	}
+
+	public UPath pathUp() {
+		final UPath path = UPath.none();
+		final double xm = width / 2;
+		final double ym = height / 2;
+
+		path.moveTo(0, height);
+
+		final double cp1x1 = ctrl;
+		final double cp1y1 = height;
+		final double cp1x2 = xm;
+		final double cp1y2 = ym + ctrl;
+		path.cubicTo(cp1x1, cp1y1, cp1x2, cp1y2, xm, ym);
+
+		final double cp2x1 = xm;
+		final double cp2y1 = ym - ctrl;
+		final double cp2x2 = width - ctrl;
+		final double cp2y2 = 0;
+		path.cubicTo(cp2x1, cp2y1, cp2x2, cp2y2, width, 0);
+
+		return path;
+	}
+
+}