From 084cabaca9a3e8cd39d99d7d4529df0094bbc5cc Mon Sep 17 00:00:00 2001
From: Rob Watson <rob@netflux.io>
Date: Thu, 30 Sep 2021 21:09:09 +0200
Subject: [PATCH] poc: Add SeekBar

---
 frontend/src/Waveform/Helpers.tsx  | 19 +++++++
 frontend/src/Waveform/SeekBar.tsx  | 82 ++++++++++++++++++++++++++++++
 frontend/src/Waveform/Waveform.tsx | 11 ++++
 3 files changed, 112 insertions(+)
 create mode 100644 frontend/src/Waveform/SeekBar.tsx

diff --git a/frontend/src/Waveform/Helpers.tsx b/frontend/src/Waveform/Helpers.tsx
index 4876e02..42177b6 100644
--- a/frontend/src/Waveform/Helpers.tsx
+++ b/frontend/src/Waveform/Helpers.tsx
@@ -1,6 +1,11 @@
 import { CanvasLogicalWidth } from './Waveform';
 import { MouseEvent } from 'react';
 
+interface Point {
+  x: number;
+  y: number;
+}
+
 // TODO: add tests
 export const mouseEventToCanvasX = (
   evt: MouseEvent<HTMLCanvasElement>
@@ -10,6 +15,20 @@ export const mouseEventToCanvasX = (
   return (elementX * CanvasLogicalWidth) / rect.width;
 };
 
+// TODO: add tests
+export const mouseEventToCanvasPoint = (
+  evt: MouseEvent<HTMLCanvasElement>
+): Point => {
+  const rect = evt.currentTarget.getBoundingClientRect();
+  const elementX = evt.clientX - rect.left;
+  const elementY = evt.clientY - rect.top;
+
+  return {
+    x: (elementX * evt.currentTarget.width) / rect.width,
+    y: (elementY * evt.currentTarget.height) / rect.height,
+  };
+};
+
 // TODO: add tests
 export const canvasXToFrame = (x: number, numFrames: number): number => {
   return Math.floor((x / CanvasLogicalWidth) * numFrames);
diff --git a/frontend/src/Waveform/SeekBar.tsx b/frontend/src/Waveform/SeekBar.tsx
new file mode 100644
index 0000000..debda82
--- /dev/null
+++ b/frontend/src/Waveform/SeekBar.tsx
@@ -0,0 +1,82 @@
+import { useRef, useEffect, useState, MouseEvent } from 'react';
+import { mouseEventToCanvasPoint } from './Helpers';
+
+interface Props {
+  duration: number;
+  style: React.CSSProperties;
+}
+
+const LogicalHeight = 200;
+const MarginX = 0;
+const MarginY = 85;
+const KnobRadius = 40;
+
+export const SeekBar: React.FC<Props> = (props: Props) => {
+  const canvasRef = useRef<HTMLCanvasElement>(null);
+  const [position, _setPosition] = useState(100);
+  const [cursor, setCursor] = useState('auto');
+
+  const secsToCanvasX = (secs: number, width: number): number => {
+    return (secs / props.duration) * width;
+  };
+
+  // draw the canvas
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (canvas == null) {
+      return;
+    }
+
+    const ctx = canvas.getContext('2d');
+    if (ctx == null) {
+      console.error('no seekbar 2d context available');
+      return;
+    }
+
+    // Set aspect ratio.
+    canvas.width = canvas.height * (canvas.clientWidth / canvas.clientHeight);
+
+    ctx.fillStyle = '#333333';
+    ctx.fillRect(0, 0, canvas.width, canvas.height);
+
+    ctx.fillStyle = 'black';
+    ctx.fillRect(
+      MarginX,
+      MarginY,
+      canvas.width - MarginX * 2,
+      canvas.height - MarginY * 2
+    );
+
+    const x = secsToCanvasX(position, canvas.width);
+    const y = LogicalHeight / 2;
+    ctx.beginPath();
+    ctx.arc(x, y, KnobRadius, 0, 2 * Math.PI, false);
+    ctx.fillStyle = 'red';
+    ctx.fill();
+  });
+
+  const style = { ...props.style, cursor: cursor };
+
+  // handlers
+
+  const handleMouseMove = (evt: MouseEvent<HTMLCanvasElement>) => {
+    const { x: _x, y: y } = mouseEventToCanvasPoint(evt);
+    // TODO: improve mouse detection around knob.
+    if (y > MarginY && y < LogicalHeight - MarginY) {
+      setCursor('pointer');
+    } else {
+      setCursor('auto');
+    }
+  };
+
+  return (
+    <>
+      <canvas
+        style={style}
+        ref={canvasRef}
+        height={LogicalHeight}
+        onMouseMove={handleMouseMove}
+      ></canvas>
+    </>
+  );
+};
diff --git a/frontend/src/Waveform/Waveform.tsx b/frontend/src/Waveform/Waveform.tsx
index 779effa..e4d4ab2 100644
--- a/frontend/src/Waveform/Waveform.tsx
+++ b/frontend/src/Waveform/Waveform.tsx
@@ -2,6 +2,7 @@ import { useEffect, useState, useRef, MouseEvent } from 'react';
 import { Waveform as WaveformOverview } from './Overview';
 import { Thumbnails } from './Thumbnails';
 import { Canvas as WaveformCanvas } from './Canvas';
+import { SeekBar } from './SeekBar';
 import { canvasXToFrame, mouseEventToCanvasX } from './Helpers';
 
 interface Props {
@@ -323,6 +324,12 @@ export const Waveform: React.FC<Props> = ({ audioContext }: Props) => {
     margin: '10px auto 0 auto',
     display: 'block',
   };
+  const seekBarStyles = {
+    width: '90%',
+    height: '50px',
+    margin: '0 auto',
+    display: 'block',
+  };
 
   return (
     <>
@@ -351,6 +358,10 @@ export const Waveform: React.FC<Props> = ({ audioContext }: Props) => {
           height={CanvasLogicalHeight}
         ></canvas>
       </div>
+      <SeekBar
+        duration={mediaSet.audio.frames / mediaSet.audio.sampleRate}
+        style={seekBarStyles}
+      />
       <div style={controlPanelStyles}>
         <button onClick={handlePlay}>Play</button>
         <button onClick={handlePause}>Pause</button>