CanvasImage

Converts image to canvas with same look.

Useful for memory optimization in case of responsive images usage. Also is good for solving Android antialiasing issue in PhoneGap or web applications.

Usage

Simpliest way to use CanvasImage is by calling new CanvasImage('selector') or new CanvasImage(DOMElement)

There is also approach to convert all images on current page. For this use CanvasImage.all()

###Memory consumption optimization use case###

#####Problem#####

Responsive images are common citezens of web applications and very often they are a bit larger than we need for particular screen size. This creates memory overusage problem for mobile devices.

For example you have universal web app which works on desktops as well as on iPhones.

Problem is that iPhone is still forced to keep large desktop image in memory.

#####Solution####

Most obvious way to fix this is to create few sets of images for different screen sizes however this is not easy to do - you will need additional files to support, styles to develop and bunch of time to spend. Here CanvasImage is a game changer.

How it works:

• Library finds all img tags on page
• Replaces them with canvas tags of same size
• Draws images content to canvases reducing size to needed one
• Removes old big images from memory

After this we have set of canvases which look absolutely like images we had before but with one difference - we removed all image data which is not needed for our current window size.

###Android anti-aliasing issue use case###

#####Problem#####

A lot of Android devices have very annoying browser behaviour - it disables antialiasing on every touch to optimize rendering. This creates some kind of blinking effect when user touches screen.

#####Solution#####

It is possible to avoid such a problem with disabling browser anti-aliasing with CSS so there will be nothing to disable then. Have sense?

Let`s add next CSS code to stylesheet:

	* {
		image-rendering: optimizeSpeed;
		image-rendering: -moz-crisp-edges;
		image-rendering: -o-crisp-edges;
		image-rendering: -webkit-optimize-contrast;
		image-rendering: optimize-contrast
		-ms-interpolation-mode: nearest-neighbor;
	}

Yes, this will work until we do not have responsive images in app. Since we will start to use them - issue will appear again. This happens because of difference between antialiasing mechanisms of CSS engine and Android WebView component. CSS antialiases images before they were scaled and browser antialiasing is being applied after scaling.

To avoid this effect you have to have images absolutely unscaled somehow. Here CanvasImage can be best approach possible beacuse it replaces scaled images with unscaled canvases.