final

Co-authored-by: Copilot <copilot@github.com>

templates/index.html

@@ -493,6 +493,7 @@
       const MIN_SPHERE_SIZE = 0.16;
       const MAX_SPHERE_SIZE = 0.62;
       const HZ_LABEL_FADE_MS = 2000;
+      const POINT_FADE_WINDOW_SEC = 2;
 
       function setFrequencyColor(color, fn, an) {
         const t = Math.min(Math.max(fn, 0), 1);
@@ -509,6 +510,22 @@
         );
       }
 
+      function syncFrequencyLegend() {
+        const gradStrip = document.querySelector(".grad-strip");
+        if (!gradStrip) return;
+
+        const samples = [0, 0.25, 0.5, 0.75, 1];
+        const c = new THREE.Color();
+        const stops = samples.map((fn) => {
+          setFrequencyColor(c, fn, 0.85);
+          return `#${c.getHexString()} ${Math.round(fn * 100)}%`;
+        });
+
+        gradStrip.style.background = `linear-gradient(to right, ${stops.join(", ")})`;
+      }
+
+      syncFrequencyLegend();
+
       // ── Build instanced visualization ────────────────────────────────────────
       // All instances are pre-loaded but initially count=0 so nothing is drawn.
       // The animation loop reveals them as the audio plays.
@@ -543,20 +560,47 @@
 
         const n = data.tn.length;
         const positions = new Float32Array(n * 3);
+        const instanceColors = new Float32Array(n * 3);
+        const instanceAlphas = new Float32Array(n);
         const sphereGeo = new THREE.SphereGeometry(1, 10, 8);
+        const baseVertexColors = new Float32Array(
+          sphereGeo.attributes.position.count * 3,
+        );
+        baseVertexColors.fill(1);
+        sphereGeo.setAttribute(
+          "color",
+          new THREE.Float32BufferAttribute(baseVertexColors, 3),
+        );
         const sphereMat = new THREE.MeshBasicMaterial({
+          color: 0xffffff,
           vertexColors: true,
-          transparent: false,
-          opacity: 1,
+          transparent: true,
+          opacity: 0.78,
+          depthWrite: false,
           fog: false,
           toneMapped: false,
         });
+        sphereMat.onBeforeCompile = (shader) => {
+          shader.vertexShader =
+            "attribute float instanceAlpha; varying float vInstanceAlpha;\n" +
+            shader.vertexShader.replace(
+              "#include <begin_vertex>",
+              "#include <begin_vertex>\n vInstanceAlpha = instanceAlpha;",
+            );
+          shader.fragmentShader =
+            "varying float vInstanceAlpha;\n" +
+            shader.fragmentShader.replace(
+              "vec4 diffuseColor = vec4( diffuse, opacity );",
+              "vec4 diffuseColor = vec4( diffuse, opacity * vInstanceAlpha );",
+            );
+        };
         audioMesh = new THREE.InstancedMesh(sphereGeo, sphereMat, n);
-        audioMesh.count = 0;
+        audioMesh.count = n;
 
         const lineGeo = new THREE.BufferGeometry();
         const lineMat = new THREE.LineBasicMaterial({
           color: 0xbfd5ff,
+          vertexColors: true,
           linewidth: 1,
           transparent: true,
           opacity: 0.32,
@@ -594,15 +638,31 @@
 
           setFrequencyColor(color, fn, an);
           audioMesh.setColorAt(i, color);
+          instanceColors[p3] = color.r;
+          instanceColors[p3 + 1] = color.g;
+          instanceColors[p3 + 2] = color.b;
+          instanceAlphas[i] = 0;
         }
 
+        audioMesh.instanceColor = new THREE.InstancedBufferAttribute(
+          instanceColors,
+          3,
+        );
+        audioMesh.geometry.setAttribute(
+          "instanceAlpha",
+          new THREE.InstancedBufferAttribute(instanceAlphas, 1),
+        );
         audioPositions = positions;
         audioMesh.instanceMatrix.needsUpdate = true;
-        audioMesh.instanceColor.needsUpdate = true;
+        if (audioMesh.instanceColor) audioMesh.instanceColor.needsUpdate = true;
         lineGeo.setAttribute(
           "position",
           new THREE.BufferAttribute(positions, 3),
         );
+        lineGeo.setAttribute(
+          "color",
+          new THREE.BufferAttribute(instanceColors, 3),
+        );
         lineGeo.setDrawRange(0, 0);
         audioLine = new THREE.Line(lineGeo, lineMat);
 
@@ -632,7 +692,7 @@
       let autoOrbit = true;
       let isPointerHeldInCanvas = false;
       let isControlInteracting = false;
-      let orbitSpeed = 0.6; // radians per second
+      let orbitSpeed = 0.1; // radians per second
       const orbitClock = new THREE.Clock();
 
       function syncAutoOrbitState() {
@@ -726,9 +786,25 @@
       function updateRevealAndTrail(nowMs) {
         const visibleCount = getVisibleCountAtCurrentTime();
         if (!audioMesh || !audioLine) return;
+        const cutoffTime = audioEl.currentTime - POINT_FADE_WINDOW_SEC;
+        const times = audioData?.t;
+        let startIndex = 0;
 
-        audioMesh.count = visibleCount;
-        audioLine.geometry.setDrawRange(0, Math.max(0, visibleCount));
+        if (times && cutoffTime > 0) {
+          let lo = 0;
+          let hi = visibleCount;
+          while (lo < hi) {
+            const mid = (lo + hi) >>> 1;
+            if (times[mid] < cutoffTime) lo = mid + 1;
+            else hi = mid;
+          }
+          startIndex = lo;
+        }
+
+        audioLine.geometry.setDrawRange(
+          startIndex,
+          Math.max(0, visibleCount - startIndex),
+        );
 
         const revealIndex = visibleCount - 1;
         if (revealIndex !== lastRevealIndex && revealIndex >= 0) {
@@ -737,6 +813,34 @@
         }
       }
 
+      function updatePointFadeByPlayback() {
+        if (!audioMesh || !audioData || audioEl.duration <= 0) return;
+        const alphaAttr = audioMesh.geometry.getAttribute("instanceAlpha");
+        if (!alphaAttr) return;
+
+        const currentT = audioEl.currentTime;
+        const isAtStart = audioEl.paused && currentT === 0;
+        const times = audioData.t;
+        const alphas = alphaAttr.array;
+
+        for (let i = 0; i < times.length; i++) {
+          if (isAtStart) {
+            alphas[i] = 0;
+            continue;
+          }
+
+          const age = currentT - times[i];
+          if (age < 0 || age > POINT_FADE_WINDOW_SEC) {
+            alphas[i] = 0;
+          } else {
+            const fade = 1 - age / POINT_FADE_WINDOW_SEC;
+            alphas[i] = fade;
+          }
+        }
+
+        alphaAttr.needsUpdate = true;
+      }
+
       function updateTimeCursorFromPlayback() {
         if (!timeCursor.visible || audioEl.duration <= 0) return;
 
@@ -768,6 +872,7 @@
 
         orbitControls.update();
         updateRevealAndTrail(nowMs);
+        updatePointFadeByPlayback();
         updateTimeCursorFromPlayback();
 
         updateHzLabel(nowMs);