From faf818e4aed98f87a05c8e3ec2fac09dcf1576f8 Mon Sep 17 00:00:00 2001
From: Rob Watson <rob@netflux.io>
Date: Sat, 11 Sep 2021 12:58:43 +0200
Subject: [PATCH] Implement basic zoom in/out

---
 frontend/src/Waveform.tsx | 77 +++++++++++++++++++++++++++------------
 1 file changed, 54 insertions(+), 23 deletions(-)

diff --git a/frontend/src/Waveform.tsx b/frontend/src/Waveform.tsx
index 998a74b..3cfc423 100644
--- a/frontend/src/Waveform.tsx
+++ b/frontend/src/Waveform.tsx
@@ -11,12 +11,20 @@ type AudioFile = {
   sampleRate: number;
 };
 
+type ZoomSettings = {
+  startFrame: number;
+  endFrame: number;
+};
+
+const defaultZoomSettings: ZoomSettings = { startFrame: 0, endFrame: 0 };
+
 export const Waveform: React.FC<WaveformProps> = ({
   audioContext,
 }: WaveformProps) => {
   const [audioFile, setAudioFile] = useState<AudioFile | null>(null);
   const [currentTime, setCurrentTime] = useState(0);
   const [audio, setAudio] = useState(new Audio());
+  const [zoomSettings, setZoomSettings] = useState(defaultZoomSettings);
 
   const waveformCanvasRef = useRef<HTMLCanvasElement>(null);
   const hudCanvasRef = useRef<HTMLCanvasElement>(null);
@@ -41,13 +49,13 @@ export const Waveform: React.FC<WaveformProps> = ({
     return Math.floor((x / canvasLogicalWidth) * audioFile.frames);
   };
 
-  const canvasXToSecs = (x: number): number => {
-    if (audioFile == null) {
-      return 0;
-    }
-    const duration = audioFile.frames / audioFile.sampleRate;
-    return (canvasXToFrame(x) / audioFile.frames) * duration;
-  };
+  // const canvasXToSecs = (x: number): number => {
+  //   if (audioFile == null) {
+  //     return 0;
+  //   }
+  //   const duration = audioFile.frames / audioFile.sampleRate;
+  //   return (canvasXToFrame(x) / audioFile.frames) * duration;
+  // };
 
   const secsToCanvasX = (canvasWidth: number, secs: number): number => {
     if (audioFile == null) {
@@ -92,10 +100,11 @@ export const Waveform: React.FC<WaveformProps> = ({
       };
 
       setAudioFile(audioFile);
+      setZoomSettings({ startFrame: 0, endFrame: audioFile.frames });
     })();
   }, [audioContext]);
 
-  // render waveform to canvas when audioData is updated:
+  // render waveform to canvas when zoom settings are updated:
   useEffect(() => {
     (async function () {
       if (audioFile == null) {
@@ -116,18 +125,21 @@ export const Waveform: React.FC<WaveformProps> = ({
         return;
       }
 
-      ctx.strokeStyle = '#00aa00';
-      ctx.fillStyle = 'black';
-      ctx.fillRect(0, 0, canvas.width, canvas.height);
+      let endFrame = zoomSettings.endFrame;
+      if (endFrame <= zoomSettings.startFrame) {
+        endFrame = audioFile.frames;
+      }
 
       const resp = await fetch(
-        `http://localhost:8888/api/peaks?video_id=${videoID}&start=0&end=${Math.round(
-          audioFile.frames
-        )}&bins=${canvas.width}`
+        `http://localhost:8888/api/peaks?video_id=${videoID}&start=${zoomSettings.startFrame}&end=${endFrame}&bins=${canvas.width}`
       );
       const peaks = await resp.json();
       console.log('respBody from peaks =', peaks);
 
+      ctx.strokeStyle = '#00aa00';
+      ctx.fillStyle = 'black';
+      ctx.fillRect(0, 0, canvas.width, canvas.height);
+
       const numChannels = peaks.length;
       const chanHeight = canvas.height / numChannels;
       for (let c = 0; c < numChannels; c++) {
@@ -144,7 +156,7 @@ export const Waveform: React.FC<WaveformProps> = ({
         }
       }
     })();
-  }, [audioFile]);
+  }, [zoomSettings]);
 
   // redraw HUD
   useEffect(() => {
@@ -163,6 +175,10 @@ export const Waveform: React.FC<WaveformProps> = ({
 
       ctx.clearRect(0, 0, canvas.width, canvas.height);
 
+      if (audioFile == null) {
+        return;
+      }
+
       const x = secsToCanvasX(canvas.width, currentTime);
 
       ctx.strokeStyle = 'red';
@@ -180,14 +196,8 @@ export const Waveform: React.FC<WaveformProps> = ({
     console.log('mousemove, x =', canvasX, 'frame =', canvasXToFrame(canvasX));
   };
 
-  const handleMouseDown = (evt: MouseEvent<HTMLCanvasElement>) => {
-    if (audioFile == null) {
-      return;
-    }
-
-    const canvasX = mouseEventToCanvasX(evt);
-    audio.currentTime = canvasXToSecs(canvasX);
-    console.log('currentTime now', canvasXToSecs(canvasX));
+  const handleMouseDown = () => {
+    return null;
   };
 
   const handleMouseUp = () => {
@@ -207,11 +217,29 @@ export const Waveform: React.FC<WaveformProps> = ({
   };
 
   const handleZoomIn = () => {
+    if (audioFile == null) {
+      return;
+    }
     console.log('zoom in');
+    const diff = zoomSettings.endFrame - zoomSettings.startFrame;
+    const endFrame = zoomSettings.startFrame + Math.floor(diff / 2);
+    const settings = { ...zoomSettings, endFrame: endFrame };
+    setZoomSettings(settings);
   };
 
   const handleZoomOut = () => {
+    if (audioFile == null) {
+      return;
+    }
     console.log('zoom out');
+    const diff = zoomSettings.endFrame - zoomSettings.startFrame;
+    const newDiff = diff * 2;
+    const endFrame = Math.min(
+      zoomSettings.endFrame + newDiff,
+      audioFile.frames
+    );
+    const settings = { ...zoomSettings, endFrame: endFrame };
+    setZoomSettings(settings);
   };
 
   // render component:
@@ -222,6 +250,7 @@ export const Waveform: React.FC<WaveformProps> = ({
     position: 'relative',
     margin: '0 auto',
   } as React.CSSProperties;
+
   const waveformCanvasProps = {
     width: '100%',
     position: 'absolute',
@@ -231,6 +260,7 @@ export const Waveform: React.FC<WaveformProps> = ({
     bottom: 0,
     zIndex: 0,
   } as React.CSSProperties;
+
   const hudCanvasProps = {
     width: '100%',
     position: 'absolute',
@@ -240,6 +270,7 @@ export const Waveform: React.FC<WaveformProps> = ({
     bottom: 0,
     zIndex: 1,
   } as React.CSSProperties;
+
   const clockTextAreaProps = { color: '#999', width: '400px' };
 
   return (