Simple HTML Canvas not showing full shape-CodePudding

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.

CodePudding user response：

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>