adds changeText to text and adds throttling function

src/shapes/primitives/text.ts

@@ -287,6 +287,16 @@ class Text implements Shape {
         return this._tex;
     }
 
+    changeText(text: string): this {
+        this._text = text;
+
+        this._textMeasurement = new TextMeasurement(config.canvasInstance!, this._tex);
+        this._textWidth = this._textMeasurement.textWidth(this._text, this._size, this._font);
+        this._textHeight = this._textMeasurement.textHeight(this._text, this._size, this._font);
+
+        return this;
+    }
+
     private boundingBox(): { minX: number, maxX: number, minY: number, maxY: number } {
         const left = this._align === 'left' ? this._x : this._align === 'center' ? this._x - this._textWidth / 2 : this._x - this._textWidth;
         const top = this._baseline === 'top' ? this._y : this._baseline === 'middle' ? this._y - this._textHeight / 2 : this._y - this._textHeight;

src/utils.ts

@@ -49,4 +49,27 @@ function extractType<T extends Object>(obj: any): T {
 }
 
 
-export default { deepCopy, extractType };
+function throttle<T extends (...args: any[]) => void>(func: T, wait: number): (...args: Parameters<T>) => void {
+    let timeout: ReturnType<typeof setTimeout> | null = null;
+    let lastCallTime: number | null = null;
+
+    return function(...args: Parameters<T>): void {
+        const now = Date.now();
+
+        if (lastCallTime && now < lastCallTime + wait) {
+            if (timeout) {
+                clearTimeout(timeout);
+            }
+            timeout = setTimeout(() => {
+                lastCallTime = Date.now();
+                func(...args);
+            }, wait - (now - lastCallTime));
+        } else {
+            lastCallTime = Date.now();
+            func(...args);
+        }
+    };
+}
+
+
+export default { deepCopy, extractType, throttle, };

test/script_test.ts

@@ -451,27 +451,45 @@ class TestScene extends Scene {
         const p = axes.point([0.5, fn(0.5)]);
         const q = axes.point([0.69, fn(0.69)]);
 
-        const pText = new Text({ text: 'P' }).nextTo(p, [-1, 1]);
-        const qText = new Text({ text: 'Q' }).nextTo(q, LEFT(1.5));
+        const pText = new Tex({ text: 'P' }).nextTo(p, [-1, 1]);
+        const qText = new Tex({ text: 'Q' }).nextTo(q, RIGHT(1.5));
         const qDot = new Dot({ center: q, color: Colors.blue() });
         const secant = new Line({ from: p, to: q, length: 6, lineColor: Colors.blue() });
+        const tangent = new TangentLine({ plot, x: 0.5, length: 4, color: Colors.pink() });
+        const tangentText = new Tex(`m`).changeColor(Colors.pink()).nextTo(tangent.to());
+        const secantText = new Tex(`m_{\sec}`).nextTo(secant.to()).changeColor(Colors.blue());
+        // const secantText = new Text(`m_{\\sec}`).nextTo(secant.to()).changeColor(Colors.blue());
 
         this.add(
             axes, plot,
 
             secant,
-            new TangentLine({ plot, x: 0.5, length: 4, color: Colors.pink() }),
+            tangent,
             new Dot({ center: p, color: Colors.pink() }),
 
             qDot,
-            pText, qText
+            pText, qText,
+            tangentText,
+            secantText,
         );
 
+        const updateText = utils.throttle(text => secantText.changeText(text), 200);
+
         this.add(new Updater((pctComplete: number, starting: boolean) => {
-            const x = math.lerp(0.5, 0.69, 1 - pctComplete);
+            const rx = math.lerp(0.5, 0.75, 1 - pctComplete);
+            const m = (25 * rx * rx - 25 * 0.5 * 0.5) / (rx - 0.5);
+
+            const x = math.lerp(0.51, 0.69, 1 - pctComplete);
             qDot.moveTo(plot.pointAtX(x));
             secant.changeEndpoints(p, qDot, true);
-        }, { duration: 3000, easing: Easing.linear, repeat: true, yoyo: true, }));
+            qText.nextTo(qDot.center(), RIGHT(), 0.3);
+            secantText.nextTo(secant.to()) //.changeText(`m_{\\sec} = ${m.toFixed(2)}`);
+
+            // console.log(m, pctComplete)
+            updateText(`m_{\\sec} = ${m.toFixed(2)}`);
+
+        }, { duration: 5000, easing: Easing.linear, repeat: true, yoyo: true, }));
+        // }, { duration: 5000, easing: x => Easing.easeStep(x, 10), repeat: true, yoyo: true, }));
     }
 }