I am trying to make a pixel art themed game in HTML5 canvas, and as part of that I take 10x20 or so sized images and draw them onto the canvas with the following code:
ctx.drawImage(image, 20, 20, 100, 200);
However the canvas uses bicubic image scaling and hence the pixel art images look terrible at 2x and up. Is there a way to force canvas to use nearest neighbor scaling or possibly use a custom method to scale images? If not does that mean the images have to be scaled beforehand in something like Paint.net?
Choose any one of the following:
Via JavaScript:
ctx.imageSmoothingEnabled = false;
Source: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#image-smoothing
On Gecko, you'll need
ctx.mozImageSmoothingEnabled = false;
Source: https://developer.mozilla.org/en/DOM/CanvasRenderingContext2D#Gecko-specific_attributes
On Webkit, you'll need
ctx.webkitImageSmoothingEnabled = false;
Source: https://bugs.webkit.org/show_bug.cgi?id=82804
I couldn't find information on support of this property on other browsers, so they probably don't support it.
Via CSS:
Another option is to use a set of CSS rules on the canvas. For example:
<canvas id="c" width="16" height="16"></canvas>
<script>
var c = document.getElementById("c"),
cx = c.getContext("2d"),
im = new Image();
im.src = "http://stackoverflow.com/favicon.ico"; // 16x16
cx.drawImage(im, 0, 0);
</script>
<style>
canvas {
width: 32px;
height: 32px;
image-rendering: optimizeSpeed;
image-rendering: crisp-edges;
image-rendering: -moz-crisp-edges;
image-rendering: -o-crisp-edges;
image-rendering: -webkit-optimize-contrast;
-ms-interpolation-mode: nearest-neighbor;
}
</style>
Source: https://developer.mozilla.org/en/CSS/image-rendering
Source: https://bugs.webkit.org/show_bug.cgi?id=56627
Via pixel routines:
Yet another option is to do it yourself using the canvas pixel manipulation routines: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#pixel-manipulation. That's a lot more work, though.