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;
         }