Enhance PanAndZoom with touch support for pinch zoom and single-finger pan (#71)

* Enhance PanAndZoom with touch support for pinch zoom and single-finger pan

* npm run format

* Fix null handling and adjust handle_zoom signature

Author: sago35

src/base/dom/pan-and-zoom.ts

@@ -40,6 +40,59 @@ export class PanAndZoom {
             (e: WheelEvent) => this.#on_wheel(e),
             { passive: false },
         );
+
+        let startDistance: number | null = null;
+        let startPosition: TouchList | null = null;
+
+        this.target.addEventListener("touchstart", (e: TouchEvent) => {
+            if (e.touches.length === 2) {
+                startDistance = this.#getDistanceBetweenTouches(e.touches);
+            } else if (e.touches.length === 1) {
+                startPosition = e.touches;
+            }
+        });
+
+        this.target.addEventListener("touchmove", (e: TouchEvent) => {
+            if (e.touches.length === 2) {
+                if (startDistance !== null) {
+                    const currentDistance = this.#getDistanceBetweenTouches(
+                        e.touches,
+                    );
+                    if (Math.abs(startDistance - currentDistance) < 10) {
+                        const scale = (currentDistance / startDistance) * 4;
+                        if (startDistance < currentDistance) {
+                            this.#handle_zoom(scale * -1);
+                        } else {
+                            this.#handle_zoom(scale);
+                        }
+                    }
+                    startDistance = currentDistance;
+                }
+            } else if (e.touches.length === 1 && startPosition !== null) {
+                const sx = startPosition[0]?.clientX ?? 0;
+                const sy = startPosition[0]?.clientY ?? 0;
+                const ex = e.touches[0]?.clientX ?? 0;
+                const ey = e.touches[0]?.clientY ?? 0;
+                if (Math.abs(sx - ex) < 100 && Math.abs(sy - ey) < 100) {
+                    this.#handle_pan(sx - ex, sy - ey);
+                }
+                startPosition = e.touches;
+            }
+        });
+
+        this.target.addEventListener("touchend", () => {
+            startDistance = null;
+            startPosition = null;
+        });
+    }
+
+    #getDistanceBetweenTouches(touches: TouchList) {
+        if (touches[0] && touches[1]) {
+            const dx = touches[0].clientX - touches[1].clientX;
+            const dy = touches[0].clientY - touches[1].clientY;
+            return Math.sqrt(dx * dx + dy * dy);
+        }
+        return 0;
     }
 
     #on_wheel(e: WheelEvent) {
@@ -109,19 +162,20 @@ export class PanAndZoom {
         }
     }
 
-    #handle_zoom(delta: number, mouse: Vec2) {
-        const mouse_world = this.camera.screen_to_world(mouse);
-
+    #handle_zoom(delta: number, mouse?: Vec2) {
         this.camera.zoom *= Math.exp(delta * -zoom_speed);
         this.camera.zoom = Math.min(
             this.max_zoom,
             Math.max(this.camera.zoom, this.min_zoom),
         );
 
-        const new_world = this.camera.screen_to_world(mouse);
-        const center_delta = mouse_world.sub(new_world);
+        if (mouse != null) {
+            const mouse_world = this.camera.screen_to_world(mouse);
+            const new_world = this.camera.screen_to_world(mouse);
+            const center_delta = mouse_world.sub(new_world);
 
-        this.camera.translate(center_delta);
+            this.camera.translate(center_delta);
+        }
 
         if (this.callback) {
             this.callback();