Simple HTML Canvas not showing full shape

Question

I am new to HTML canvas, I'm trying to draw a cylinder with different colors using JavaScript, I can see the drawing but the shape is not displayed fully, it is supposed to be a fully illustrated shape with colors. I tried to change the width and height settings but it stretched the shape itself.

 var canvas = document.getElementById("cylinder"); var ctx = canvas.getContext("2d"); drawCylinder(canvas, ctx, "lightblue", "black", 3); function drawCylinder(canvas, ctx, fill, border, lineWidth, r, centX, centY) { //canvas.width = 160; var centX = 0; var centY = -100; var r = 30; ctx.translate(canvas.width / 2, canvas.height / 2); ctx.scale(6, 1); ctx.beginPath(); ctx.arc(centX, centY, r, 0, 2 * Math.PI, false); ctx.restore(); ctx.fillStyle = 'YellowGreen'; ctx.fill(); ctx.lineWidth = 7; ctx.strokeStyle = 'GainsBoro'; ctx.stroke(); ctx.save(); ctx.translate(canvas.width / 2, canvas.height / 2); ctx.scale(6, 1); ctx.beginPath(); ctx.arc(centX, 100, r, 0, 2 * Math.PI, false); ctx.restore(); ctx.fillStyle = 'MediumSlateBlue'; ctx.fill(); ctx.lineWidth = 7; ctx.strokeStyle = 'GainsBoro'; ctx.stroke(); ctx.save(); ctx.lineWidth = 3; ctx.strokeStyle = 'Black'; ctx.moveTo(105, 150); ctx.lineTo(105, 352); ctx.moveTo(474, 150); ctx.lineTo(474, 352); ctx.stroke(); ctx.translate(canvas.width / 2, canvas.height / 2); ctx.scale(6, 1); ctx.beginPath(); ctx.arc(centX, centY+2, r+0.8, 0, Math.PI, false); ctx.restore(); ctx.lineWidth = 4; ctx.strokeStyle = 'Black'; ctx.stroke(); ctx.save(); ctx.translate(canvas.width / 2, canvas.height / 2); ctx.scale(6, 1); ctx.beginPath(); ctx.arc(centX, 100+2, r+0.8, 0, Math.PI, false); ctx.restore(); ctx.lineWidth = 4; ctx.strokeStyle = 'Black'; }

 <div> <canvas id="cylinder" width="300" height="400"></canvas> </div>

I'm not sure why it displays like this, can you please help the brother out.

The canvas should look like an image below.

Answer 1

You have a pretty unique way of drawing a cylinder. Of course you can do it by first drawing a circle and scaling the context vertically afterwards to ultimately stretch the circle to an ellipse but let's do it a little different.

Out of the box the CanvasRenderingContext2D has a built-in method to draw an ellipse, conveniently called ellipse() .

So you can start by drawing an ellipse for the top, another ellipse for the bottom and finally connect those with a black outline.

Something like:

 var canvas = document.getElementById("cylinder"); var ctx = canvas.getContext("2d"); drawCylinder(canvas, ctx, "lightblue", "black", 7, 100, 0, -100); function drawCylinder(canvas, ctx, fill, border, lineWidth, r, centX, centY) { ctx.translate(canvas.width / 2, canvas.height / 2); ctx.lineWidth = lineWidth; ctx.beginPath(); ctx.ellipse(centX, centY, r, r / 5, 0, 0, 2 * Math.PI); ctx.fillStyle = 'YellowGreen'; ctx.strokeStyle = 'GainsBoro'; ctx.fill(); ctx.stroke(); ctx.closePath(); ctx.beginPath(); ctx.ellipse(centX, centY + 100, r, r / 5, 0, 0, 2 * Math.PI); ctx.fillStyle = 'MediumSlateBlue'; ctx.strokeStyle = 'GainsBoro'; ctx.fill(); ctx.stroke(); ctx.closePath(); ctx.lineWidth = 1; ctx.strokeStyle = 'Black'; ctx.beginPath(); ctx.ellipse(centX, centY, r + lineWidth / 2, r / 5 + lineWidth / 2, 0, 0, 1 * Math.PI); ctx.stroke(); ctx.closePath(); ctx.beginPath(); ctx.ellipse(centX, centY + 100, r + lineWidth / 2, r / 5 + lineWidth / 2, 0, 0, 1 * Math.PI); ctx.stroke(); ctx.closePath(); ctx.beginPath(); ctx.moveTo(centX - r - lineWidth / 2, centY); ctx.lineTo(centX - r - lineWidth / 2, centY + 100); ctx.stroke(); ctx.closePath(); ctx.beginPath(); ctx.moveTo(centX + r + lineWidth / 2, centY); ctx.lineTo(centX + r + lineWidth / 2, centY + 100); ctx.stroke(); ctx.closePath(); }

 <canvas id="cylinder" width="300" height="400"></canvas>