I'm trying to resize a <canvas>
with an image already drawn, but I'm misunderstanding how to use the canvas.scale()
method because it doesn't shrink...
Code:
ImageRender.prototype.resizeTo = function () {
var canvas = $('#myCanvas')[0];
var ctx = canvas.getContext("2d");
//current image
var currImg = ctx.getImageData(0, 0, canvas.width, canvas.height);
//
var tempCanvas = $('canvas')[0];
var tempCtx = tempCanvas.getContext("2d");
tempCtx.putImageData(currImg, 0, 0)
//
ctx.scale(0.5, 0.5);
//redraw
ctx.drawImage(tempCanvas, 0, 0);
};
What am I overlooking?
Thanks!
The scale() method scales the current drawing, bigger or smaller. Note: If you scale a drawing, all future drawings will also be scaled. The positioning will also be scaled. If you scale(2,2); drawings will be positioned twice as far from the left and top of the canvas as you specify.
With the Select and Move Tool, click the canvas size label or border to select the canvas. Click the canvas border handles to resize the canvas dynamically. When you drag the border handles without using any keyboard modifiers, the canvas resizes non-uniformly. Hold Shift to constrain the resize proportions.
One of the simplest ways to resize an image in the HTML is using the height and width attributes on the img tag. These values specify the height and width of the image element. The values are set in px i.e. CSS pixels.
You can scale your canvas with content by "bouncing" the content off a temporary canvas while you resize the original canvas. This save+redraw process is necessary because canvas content is automatically cleared when you resize the canvas width or height.
Example code:
var myCanvas=document.getElementById("canvas");
var ctx=myCanvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
var tempCanvas=document.createElement("canvas");
var tctx=tempCanvas.getContext("2d");
var img=new Image();
img.crossOrigin='anonymous';
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/multple/Dog-With-Cute-Cat.jpg";
function start(){
myCanvas.width=img.width;
myCanvas.height=img.height;
ctx.drawImage(img,0,0);
resizeTo(myCanvas,0.50);
}
function resizeTo(canvas,pct){
var cw=canvas.width;
var ch=canvas.height;
tempCanvas.width=cw;
tempCanvas.height=ch;
tctx.drawImage(canvas,0,0);
canvas.width*=pct;
canvas.height*=pct;
var ctx=canvas.getContext('2d');
ctx.drawImage(tempCanvas,0,0,cw,ch,0,0,cw*pct,ch*pct);
}
body{ background-color: ivory; }
#canvas{border:1px solid red; margin:0 auto; }
<h4>Canvas resized to 50%</h4>
<canvas id="canvas" width=300 height=300></canvas>
<h4>Img with original image</h4>
<img src='https://dl.dropboxusercontent.com/u/139992952/multple/Dog-With-Cute-Cat.jpg'>
Simpler way would be using the extra parameters of drawImage()
. 4th and 5th parameters let you set the final width and height.
Also, you can paint an image (or a canvas) directly, without the need of getting the ImageData.
Also(2), I think you may want to resize the canvas too (just use its width and height properties)
https://jsfiddle.net/mezeL06o/
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With