draw path of square

draw.js

@@ -9,34 +9,46 @@ class Drawing {
     this.stopButton.onclick = () => this.stop();
     this.stopButton.innerHTML = "Stop";
     this.canvas = document.createElement('canvas');
-    this.canvas.width = 200;
-    this.canvas.height = 200;
     buttonsDiv.appendChild(this.startButton);
     buttonsDiv.appendChild(this.stopButton);
     div.appendChild(buttonsDiv);
     div.appendChild(this.canvas);
     document.body.appendChild(div);
     this.ctx = this.canvas.getContext('2d');
-    this.offset = {x: 0, y: 0};
     this.sequence = [];
     this.t = 0;
     this.rt = 0;
     this.dt = 0;
     this.points = {};
     this.stopped = true;
+    this.frame = [[-50, -50], [150, 150]];
+    this.scale = 1.0;
+    this.canvas.width = (this.frame[1][0] - this.frame[0][0]) * this.scale;
+    this.canvas.height = (this.frame[1][1] - this.frame[0][1]) * this.scale;
+    this.speed = 1.0;
   }
 
   pixel([x, y]) {
     return [
-      this.offset.x + x, 
-      this.canvas.height - this.offset.y - y
+      (x - this.frame[0][0]) * this.scale, 
+      this.canvas.height - (y - this.frame[0][1]) * this.scale
     ];
   }
+  
+  setSpeed(speed) {
+    this.speed = speed;
+  }
 
-  setOffset([x, y]) {
-    this.sequence.push(() => {
-      this.offset = {x, y};
-    });
+  setFrame([x1, y1], [x2, y2]) {
+    this.frame = [[x1, y1], [x2, y2]];
+    this.canvas.width = (this.frame[1][0] - this.frame[0][0]) * this.scale;
+    this.canvas.height = (this.frame[1][1] - this.frame[0][1]) * this.scale;
+  }
+
+  setScale(zoom) {
+    this.scale = zoom;
+    this.canvas.width = (this.frame[1][0] - this.frame[0][0]) * this.scale;
+    this.canvas.height = (this.frame[1][1] - this.frame[0][1]) * this.scale;
   }
 
   setStroke(style, width) {
@@ -72,8 +84,10 @@ class Drawing {
     });
   }
   
-  oscillatingValue(x1, x2, period) {
-    return x1 + (x2 - x1) * Math.sin(2*Math.PI*this.t/period);
+  oscillatingValue(x1, x2, period, initialPhase = 0) {
+    const center = (x1 + x2) / 2;
+    const amplitude = (x2 - x1) / 2;
+    return center + amplitude * Math.sin(2*Math.PI*this.t/period + initialPhase);
   }
 
   oscillatingPoint([x1, y1], [x2, y2], period) {
@@ -83,16 +97,47 @@ class Drawing {
   }
 
   square(p) {
+    let history = [];
+    let maxAge = 2500;
+    let dashLength = 5;
+    let distance = 0;
+    let width = 10;
+    let height = 10;
     this.sequence.push(() => {
       const [x, y] = this.getPoint(p);
-      this.ctx.fillRect(...this.pixel([x - 5, y - 5]), 10, 10);
+      this.ctx.fillRect(...this.pixel([x - width / 2, y + height / 2]), width * this.scale, height * this.scale);
+      let ds = 0;
+      if (history.length) {
+        const dx = x - history[history.length - 1].p[0];
+        const dy = y - history[history.length - 1].p[1];
+        ds = Math.sqrt(dx**2 + dy**2);
+      }
+      distance += ds;
+      history.push({t: this.t, p: [x, y], distance});
+      const oldest = history.findIndex(({t}) => this.t - t <= maxAge);
+      if (oldest >= 0) {
+        history = history.slice(oldest);
+      }
+      this.ctx.strokeStyle = 'black';
+      this.ctx.lineWidth = 1;
+      this.ctx.beginPath();
+      this.ctx.moveTo(...this.pixel(history[0].p));
+      for (let i = 1; i < history.length; i++) {
+        if (Math.floor(history[i].distance / dashLength) % 2) {
+          this.ctx.moveTo(...this.pixel(history[i].p));
+        } else {
+          this.ctx.lineTo(...this.pixel(history[i].p));
+        }
+      }
+      this.ctx.stroke();
     })
   }
 
   circle(p) {
+    const radius = 5;
     this.sequence.push(() => {
       this.ctx.beginPath();
-      this.ctx.ellipse(...this.pixel(this.getPoint(p)), 5, 5, 0, 0, 2*Math.PI);
+      this.ctx.ellipse(...this.pixel(this.getPoint(p)), radius * this.scale, radius * this.scale, 0, 0, 2*Math.PI);
       this.ctx.fill();
     })
   }
@@ -132,7 +177,7 @@ class Drawing {
           this.dt = 0;
           this.elideInterval = false;
         } else {
-          this.dt = rt - this.rt + elapsed;
+          this.dt = (rt - this.rt + elapsed) * this.speed;
         }
         this.t += this.dt;
         this.rt = rt;

test.html

@@ -10,17 +10,15 @@
 <body>
   <script>
     const d = new Drawing();
-    console.log('drawing', d);
-    d.setOffset([50, 50]);
     d.setStroke('black', 4);
     d.polyline([0, 100], [0, 0], [100, 0]);
-    d.definePoint('p1', () => d.oscillatingPoint([75, 125], [125, 125], 5000));
+    d.definePoint('p1', () => d.oscillatingPoint([25, 100], [100, 100], 5000));
     d.setStroke('red', 2);
     d.line([0, 0], 'p1');
     d.setFill('blue');
     d.definePoint('p2', () => {
       const [x, y] = d.getPoint('p1');
-      return [x, y - 25];
+      return [x, y - d.oscillatingValue(10, 40, 5000 / 3, Math.PI / 2)];
     });
     d.square('p2');
     d.setFill('cyan');