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function renderToCanvas(img, options) {
if (!img) return
options = options || {}
// Canvas max size for any side
var maxSize = 2000
var canvas = document.createElement('canvas')
var ctx = canvas.getContext('2d')
var initialScale = options.scale || 1
// Scale to needed to constrain canvas to max size
var scale = getScale(img.width * initialScale,
img.height * initialScale, maxSize, maxSize)
// Still need to apply the user defined scale
scale *= initialScale
var width = canvas.width = Math.round(img.width * scale)
var height = canvas.height = Math.round(img.height * scale)
var correctOrientation = options.correctOrientation
var jpeg = !!img.src.match(/data:image\/jpeg|\.jpeg$|\.jpg$/i)
var dataURI = !!img.src.match(/^data:/)
ctx.save()
// Can only correct orientation on JPEGs represented as dataURIs
// for the time being
if (correctOrientation && jpeg && dataURI) {
applyOrientationCorrection()
}
// Resize image if too large
if (scale !== 1) {
ctx.scale(scale, scale)
}
ctx.drawImage(img, 0, 0)
ctx.restore()
return canvas
function applyOrientationCorrection() {
var orientation = getOrientation(img.src)
// Only apply transform if there is some non-normal orientation
if (orientation && orientation !== 1) {
var transform = orientationToTransform[orientation]
var rotation = transform.rotation
var mirror = transform.mirror
var flipAspect = rotation === 90 || rotation === 270
if (flipAspect) {
// Fancy schmancy swap algo
canvas.width = canvas.height + canvas.width
canvas.height = canvas.width - canvas.height
canvas.width -= canvas.height
}
if (rotation > 0) {
applyRotation(rotation)
}
if (mirror) {
// TODO This is broken. Not sure how to apply this transform
// No biggie, we don't run into this case ATM
// applyMirror()
}
}
}
/**
* Some images are friggin rotated n shit! (iOS)
* wut the heck
* dang it
* man
* read the EXIF data
* return EXIF orientation value
*/
function getOrientation(uri) {
var exif = new ExifReader
// Split off the base64 data
var base64String = uri.split(',')[1]
// Read off first 128KB, which is all we need to
// get the EXIF data
var arr = base64ToUint8Array(base64String, 0, Math.pow(2, 17))
try {
exif.load(arr.buffer)
return exif.getTagValue('Orientation')
} catch (err) {
return 1
}
}
/**
* Apply rotation such that rotated image will be
* centered in canvas
*/
function applyRotation(deg) {
var radians = deg * (Math.PI / 180)
if (deg === 90) {
ctx.translate(canvas.width, 0)
} else if (deg === 180) {
ctx.translate(canvas.width, canvas.height)
} else if (deg == 270) {
ctx.translate(0, canvas.height)
}
ctx.rotate(radians)
}
function applyMirror() {
ctx.scale(-1, 1)
}
}
function base64ToUint8Array(string, start, finish) {
var start = start || 0
var finish = finish || string.length
// atob that shit
var binary = atob(string)
var buffer = new Uint8Array(binary.length)
for (var i = start; i < finish; i++) {
buffer[i] = binary.charCodeAt(i)
}
return buffer
}
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