illustrating a large image on a canvas

When I initially drew an image on the canvas, it looked like this: https://i.sstatic.net/t6sIC.png Now, I am attempting to reload the same image into the canvas, and it appears like this: https://i.sstatic.net/xLiO7.png Here is my code:

var ctx = element.childNodes[i + 1].children[0].firstElementChild;
if (ctx.getContext) {
  ctx = ctx.getContext('2d');
  var img1 = new Image();
  img1.onload = function() {
    ctx.drawImage(img1, ctx.canvas.width, ctx.canvas.height);
  }
}

I attempted to set the canvas height and width to match the image, but it did not work as expected.

var ctx = element.childNodes[i + 1].children[0].firstElementChild;
if (ctx.getContext) {
  ctx = ctx.getContext('2d');
  var img1 = new Image();
  img1.onload = function() {
    img1.width = ctx.canvas.width;
    img1.height = ctx.canvas.height;
    ctx.drawImage(img1, ctx.canvas.width, ctx.canvas.height);
  }
}

After trying this approach, the image loaded correctly but when attempting to redraw the image, it appeared in a different position than expected.

var ctx = element.childNodes[i + 1].children[0].firstElementChild;
if (ctx.getContext) {
  ctx = ctx.getContext('2d');
  var img1 = new Image();
  img1.onload = function() {
    ctx.canvas.width = img1.width;
    ctx.canvas.height = img1.height;
    ctx.drawImage(img1, ctx.canvas.width, ctx.canvas.height);
  }
}

https://i.sstatic.net/twmq6.png

Answer №1

When using the

CanvasRenderingContext2D.drawImage()
method, it is important to remember that 5 parameters are required for this scenario. The first parameter is the image itself, while the remaining 4 parameters represent the x position, y position, width, and height of the image.

To draw the image in the top-left corner, you can use the code snippet

drawImage(image, 0, 0, image.width, image.height)
.

const canvas = document.querySelector('canvas');
const context = canvas.getContext('2d');

const image = new Image();
image.src = 'http://www.fillmurray.com/g/600/300';
image.onload = () => {
  canvas.width = image.width;
  canvas.height = image.height;
  context.drawImage(image, 0, 0, image.width, image.height);
};
<canvas></canvas>

It is also recommended to add some CSS styles to ensure that the <canvas> element is appropriately sized.

canvas {
   width: 100%;
   height: auto;
}

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