datasets for sketches

docs/chapters/arclength/draw-slices.js

@@ -0,0 +1,45 @@
+setup() {
+    this.steps = getParameter(`steps`, 10);
+}
+
+draw() {
+    clear();
+
+    const w = this.width;
+    const h = this.height;
+    const a = h/3;
+
+    let trueArea = (4 * a).toFixed(2);
+    let computedArea = this.drawSlices(w, h, a, this.steps).toFixed(2);
+
+    setStroke(`black`);
+    line(0, h/2, w, h/2);
+
+    noFill();
+    setStroke(`black`);
+    start();
+    for(let i=0, f=TAU/w; i<w; i++) {
+        vertex(i, sin(i*f) * a + h/2);
+    }
+    end();
+
+    setFill(`black`);
+    text(`Approximating with ${this.steps} strips: ${computedArea} (true area: ${trueArea}`, w/2, h-10, CENTER);
+}
+
+drawSlices(w, h, a, n) {
+    if (n < 50) setStroke(`white`);
+
+    let area = 0;
+    let step = w/n;
+    for(let i=0, f=TAU/w, c, y; i<w; i += step) {
+        c = `rgba(150,150,255,${0.4 + 0.3 * random()}`;
+        if (n > 50) setStroke(c);
+        setFill(c);
+        y = sin((i+step/2) * f) * a;
+        rect(i, h/2, step, y);
+        area += abs(step * f * y);
+    }
+
+    return area;
+}