error-only for http-server, better parameter parsing for sketch markup

docs/chapters/aligning/aligning.js

@@ -0,0 +1,64 @@
+let curve;
+
+setup() {
+    const type = this.parameters.type ?? `quadratic`;
+    curve = (type === `quadratic`) ? Bezier.defaultQuadratic(this) : Bezier.defaultCubic(this);
+    setMovable(curve.points);
+}
+
+draw() {
+    resetTransform();
+    clear();
+    curve.drawSkeleton();
+    curve.drawCurve();
+    curve.drawPoints();
+
+    translate(this.width/2, 0);
+    line(0,0,0,this.height);
+
+    this.drawRTCurve(
+        this.rotatePoints(
+            this.translatePoints(
+                curve.points
+            )
+        )
+    );
+}
+
+translatePoints(points) {
+    // translate to (0,0)
+    let m = points[0];
+    return points.map(v => {
+        return {
+            x: v.x - m.x,
+            y: v.y - m.y
+        }
+    });
+}
+
+rotatePoints(points) {
+    // rotate so that last point is (...,0)
+    let degree = curve.points.length - 1;
+    let dx = points[degree].x;
+    let dy = points[degree].y;
+    let a = atan2(dy, dx);
+    return points.map(v => {
+        return {
+            x: v.x * cos(-a) - v.y * sin(-a),
+            y: v.x * sin(-a) + v.y * cos(-a)
+        };
+    });
+}
+
+drawRTCurve(points) {
+    let degree = curve.points.length - 1;
+    let ncurve = new Bezier(this, points);
+    translate(60, this.height/2);
+    setStroke(`grey`);
+    line(0,-this.height,0,this.height);
+    line(-60,0,this.width,0);
+    ncurve.drawCurve();
+    setFill(`black`);
+    text(`(0,0)`, 5,15);
+    text(`(${points[degree].x|0},0)`, points[degree].x, -5, CENTER);
+}