add interpolation to cursor reticles

cursor reticles are now interpolated to the update interval, so they should be smooth at > 60 fps

static/framework.js

@@ -20,18 +20,34 @@ export function listen(...listenerSpecs) {
 }
 
 export function debounce(time, fn) {
+    // This function is kind of tricky, but basically:
+    //
+    // - we want to guarantee `fn` is called at most once every `time` milliseconds
+    // - at the same time, in case debounced `fn` is called during an ongoing timeout, we want to
+    //   queue up another run, and run it immediately after `time` passes
+    //   - at the same time, in case this catch-up condition occurs, we must also ensure there's a
+    //     delay after `fn` is called
+    //
+    // yielding the recursive solution below.
+
     let timeout = null;
     let queued = null;
+
+    const callFn = (args) => {
+        fn(...args);
+
+        timeout = setTimeout(() => {
+            timeout = null;
+            if (queued != null) {
+                callFn(queued);
+                queued = null;
+            }
+        }, time);
+    };
+
     return (...args) => {
         if (timeout == null) {
-            fn(...args);
-            timeout = setTimeout(() => {
-                timeout = null;
-                if (queued != null) {
-                    fn(...queued);
-                    queued = null;
-                }
-            }, time);
+            callFn(args);
         } else {
             queued = args;
         }

static/index.js

@@ -26,6 +26,7 @@ let connectionStatus = main.querySelector("rkgk-connection-status");
 
 document.getElementById("js-loading").remove();
 reticleRenderer.connectViewport(canvasRenderer.viewport);
+reticleRenderer.updateInterval = updateInterval;
 
 function updateUrl(session, viewport) {
     let url = new URL(window.location);
@@ -231,7 +232,7 @@ function readUrl(urlString) {
         }
     });
 
-    let reportCursor = debounce(updateInterval, (x, y) => session.sendCursor(x, y));
+    let reportCursor = debounce(updateInterval, (x, y) => session.sendCursor(x, y), console.log);
     canvasRenderer.addEventListener(".cursor", async (event) => {
         reportCursor(event.x, event.y);
     });

static/reticle-renderer.js

@@ -7,6 +7,12 @@ export class Reticle extends HTMLElement {
 export class ReticleCursor extends Reticle {
     #container;
 
+    #lastX = 0;
+    #lastY = 0;
+    #targetX = 0;
+    #targetY = 0;
+    #lastUpdate = 0;
+
     constructor(nickname) {
         super();
         this.nickname = nickname;
@@ -38,23 +44,39 @@ export class ReticleCursor extends Reticle {
     }
 
     setCursor(x, y) {
-        this.x = x;
-        this.y = y;
+        this.#lastX = this.#targetX;
+        this.#lastY = this.#targetY;
+        this.#targetX = x;
+        this.#targetY = y;
+        this.#lastUpdate = performance.now();
         this.dispatchEvent(new Event(".update"));
     }
 
-    render(viewport, windowSize) {
-        let [viewportX, viewportY] = viewport.toScreenSpace(this.x, this.y, windowSize);
+    render(viewport, updateInterval, windowSize) {
+        let sinceLastUpdate = performance.now() - this.#lastUpdate;
+        let t = Math.max(0, Math.min(1, sinceLastUpdate / updateInterval));
+
+        let x = lerp(this.#lastX, this.#targetX, t);
+        let y = lerp(this.#lastY, this.#targetY, t);
+
+        let [viewportX, viewportY] = viewport.toScreenSpace(x, y, windowSize);
         this.style.transform = `translate(${viewportX}px, ${viewportY}px)`;
+
+        let needsRerender = t < 1; // if the linear animation isn't yet done
+        return needsRerender;
     }
 }
 
 customElements.define("rkgk-reticle-cursor", ReticleCursor);
 
 export class ReticleRenderer extends HTMLElement {
+    updateInterval = 1000 / 10; // a really wrong value, you should definitely override this
+
     #reticles = new Set();
     #reticlesDiv;
 
+    #animatingReticles = new Set();
+
     connectedCallback() {
         this.#reticlesDiv = this.appendChild(document.createElement("div"));
         this.#reticlesDiv.classList.add("reticles");
@@ -72,13 +94,13 @@ export class ReticleRenderer extends HTMLElement {
     addReticle(reticle) {
         if (!this.#reticles.has(reticle)) {
             reticle.addEventListener(".update", () => {
-                if (this.viewport != null) {
-                    reticle.render(this.viewport, {
-                        width: this.clientWidth,
-                        height: this.clientHeight,
-                    });
+                let needsKickstart = this.#animatingReticles.size == 0;
+                this.#animatingReticles.add(reticle);
+                if (needsKickstart) {
+                    this.#tickAnimatingReticles();
                 }
             });
+
             this.#reticles.add(reticle);
             this.#reticlesDiv.appendChild(reticle);
         }
@@ -91,6 +113,25 @@ export class ReticleRenderer extends HTMLElement {
         }
     }
 
+    #tickAnimatingReticles() {
+        if (this.viewport == null) return;
+
+        let windowSize = {
+            width: this.clientWidth,
+            height: this.clientHeight,
+        };
+        for (let reticle of this.#animatingReticles) {
+            let needsUpdate = reticle.render(this.viewport, this.updateInterval, windowSize);
+            if (!needsUpdate) {
+                this.#animatingReticles.delete(reticle);
+            }
+        }
+
+        if (this.#animatingReticles.size > 0) {
+            requestAnimationFrame(() => this.#tickAnimatingReticles());
+        }
+    }
+
     render() {
         if (this.viewport == null) {
             console.debug("viewport is disconnected, skipping transform update");
@@ -99,9 +140,13 @@ export class ReticleRenderer extends HTMLElement {
 
         let windowSize = { width: this.clientWidth, height: this.clientHeight };
         for (let reticle of this.#reticles.values()) {
-            reticle.render(this.viewport, windowSize);
+            reticle.render(this.viewport, this.updateInterval, windowSize);
         }
     }
 }
 
 customElements.define("rkgk-reticle-renderer", ReticleRenderer);
+
+function lerp(a, b, t) {
+    return a + (b - a) * t;
+}