The JavaScript function to plot a sine wave is Math.sin(), which may be called repeatedly and given a different y-axis starting point. Furthermore, the draw() function makes repeated calls via window.requestAnimationFrame(draw).
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May 12, 2022 13:25
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Oscillating Sine Wave Rendered with JavaScript
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| license: cc-by-4.0 |
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <title>Sine Wave</title> | |
| <script type="text/javascript"> | |
| function showAxes(ctx,axes) { | |
| var width = ctx.canvas.width; | |
| var height = ctx.canvas.height; | |
| var xMin = 0; | |
| ctx.beginPath(); | |
| ctx.strokeStyle = "rgb(128,128,128)"; | |
| // X-Axis | |
| ctx.moveTo(xMin, height/2); | |
| ctx.lineTo(width, height/2); | |
| // Y-Axis | |
| ctx.moveTo(width/2, 0); | |
| ctx.lineTo(width/2, height); | |
| // Starting line | |
| ctx.moveTo(0, 0); | |
| ctx.lineTo(0, height); | |
| ctx.stroke(); | |
| } | |
| function drawPoint(ctx, y) { | |
| var radius = 3; | |
| ctx.beginPath(); | |
| // Hold x constant at 4 so the point only moves up and down. | |
| ctx.arc(4, y, radius, 0, 2 * Math.PI, false); | |
| ctx.fillStyle = 'red'; | |
| ctx.fill(); | |
| ctx.lineWidth = 1; | |
| ctx.stroke(); | |
| } | |
| function plotSine(ctx, xOffset, yOffset) { | |
| var width = ctx.canvas.width; | |
| var height = ctx.canvas.height; | |
| var scale = 20; | |
| ctx.beginPath(); | |
| ctx.lineWidth = 2; | |
| ctx.strokeStyle = "rgb(66,44,255)"; | |
| // console.log("Drawing point..."); | |
| // drawPoint(ctx, yOffset+step); | |
| var x = 4; | |
| var y = 0; | |
| var amplitude = 40; | |
| var frequency = 20; | |
| //ctx.moveTo(x, y); | |
| ctx.moveTo(x, 50); | |
| while (x < width) { | |
| y = height/2 + amplitude * Math.sin((x+xOffset)/frequency); | |
| ctx.lineTo(x, y); | |
| x++; | |
| // console.log("x="+x+" y="+y); | |
| } | |
| ctx.stroke(); | |
| ctx.save(); | |
| console.log("Drawing point at y=" + y); | |
| drawPoint(ctx, y); | |
| ctx.stroke(); | |
| ctx.restore(); | |
| } | |
| function draw() { | |
| var canvas = document.getElementById("canvas"); | |
| var context = canvas.getContext("2d"); | |
| context.clearRect(0, 0, 500, 500); | |
| showAxes(context); | |
| context.save(); | |
| plotSine(context, step, 50); | |
| context.restore(); | |
| step += 4; | |
| window.requestAnimationFrame(draw); | |
| } | |
| function spirograph() { | |
| var canvas2 = document.getElementById("canvas2"); | |
| var context = canvas2.getContext("2d"); | |
| showAxes(context); | |
| context.save(); | |
| // var imageData = context.getImageData(0, 0, canvas.width, canvas.height); | |
| var step = 4; | |
| for (var i = -4; i < canvas.height; i += step) { | |
| // context.putImageData(imageData, 0, 0); | |
| plotSine(context, i, 54 + i); | |
| } | |
| } | |
| function init() { | |
| window.requestAnimationFrame(draw); | |
| spirograph(); | |
| } | |
| var step = -4; | |
| </script> | |
| </head> | |
| <body onload="init()"> | |
| <h3>Oscillating Sine Wave</h3> | |
| <canvas id="canvas" width="500" height="100"></canvas> | |
| <p/> | |
| <h3>Multiple Sine Waves</h3> | |
| <canvas id="canvas2" width="500" height="100"/> | |
| </body> | |
| </html> |
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