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December 13, 2020 16:13
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import {ILTRect} from './rects/ILTRect'; | |
import {Preconditions} from '../Preconditions'; | |
import {DataURL, DataURLs} from './DataURLs'; | |
import {IDimensions} from "./IDimensions"; | |
import {ImageType} from "./ImageType"; | |
const DEFAULT_IMAGE_TYPE = 'image/png'; | |
const DEFAULT_IMAGE_QUALITY = 1.0; | |
export type RawImageData = ArrayBuffer | DataURL | HTMLImageElement; | |
export interface ImageData { | |
/** | |
* The actual data of the image. | |
*/ | |
readonly data: ArrayBuffer | DataURL; | |
/** | |
* The internal format of the 'data' | |
*/ | |
readonly format: 'arraybuffer' | 'dataurl'; | |
readonly type: ImageType; | |
readonly width: number; | |
readonly height: number; | |
} | |
export namespace ImageDatas { | |
export function toDataURL(image: ImageData): string { | |
switch (image.format) { | |
case "arraybuffer": | |
return DataURLs.encode(<ArrayBuffer> image.data, image.type); | |
case "dataurl": | |
return <string> image.data; | |
} | |
} | |
} | |
/** | |
* Functions for working with canvas objects, extracting screenshots, etc. | |
*/ | |
export namespace Canvases { | |
// https://github.com/burtonator/pdf-annotation-exporter/blob/master/webapp/js/pdf-loader.js | |
// https://github.com/burtonator/pdf-annotation-exporter/blob/master/webapp/js/extractor.js | |
// https://github.com/burtonator/pdf-annotation-exporter/blob/master/webapp/js/debug-canvas.js | |
/** | |
* Take a canvas or an ArrayBuffer and convert it to a data URL without | |
* limitations on the size of the URL. | |
*/ | |
export async function toDataURL(data: HTMLCanvasElement | ArrayBuffer, | |
opts: ImageOpts = new DefaultImageOpts()): Promise<string> { | |
// https://developer.mozilla.org/en-US/docs/Web/API/Blob | |
const dataToArrayBuffer = async (): Promise<ArrayBuffer> => { | |
if (data instanceof HTMLCanvasElement) { | |
return await toArrayBuffer(data, opts); | |
} | |
return data; | |
}; | |
const ab = await dataToArrayBuffer(); | |
return DataURLs.encode(ab, DEFAULT_IMAGE_TYPE); | |
} | |
export function toArrayBuffer(canvas: HTMLCanvasElement, | |
opts: ImageOpts = new DefaultImageOpts()): Promise<ArrayBuffer> { | |
// https://developer.mozilla.org/en-US/docs/Web/API/Blob | |
// | |
return new Promise((resolve, reject) => { | |
canvas.toBlob((blob) => { | |
if (blob) { | |
const reader = new FileReader(); | |
reader.addEventListener("onloadstart", (err) => { | |
reject(err); | |
}); | |
reader.addEventListener("loadend", () => { | |
const ab = <ArrayBuffer> reader.result; | |
resolve(ab); | |
}); | |
reader.addEventListener("onerror", (err) => { | |
reject(err); | |
}); | |
reader.addEventListener("onabort", (err) => { | |
reject(err); | |
}); | |
reader.readAsArrayBuffer(blob); | |
} else { | |
reject(new Error("No blob received from canvas.")); | |
} | |
}, opts.type, opts.quality); | |
}); | |
} | |
async function createImageElementFromDataURL(image: DataURL): Promise<HTMLImageElement> { | |
return new Promise<HTMLImageElement>((resolve, reject) => { | |
const img = document.createElement("img") as HTMLImageElement; | |
img.src = image; | |
img.onload = () => resolve(img); | |
img.onerror = (err) => reject(err); | |
img.onabort = (err) => reject(err); | |
return img; | |
}); | |
} | |
async function createImageElement(image: RawImageData): Promise<HTMLImageElement> { | |
if (image instanceof HTMLImageElement) { | |
// we're done... | |
return image; | |
} | |
if (image instanceof ArrayBuffer) { | |
const dataURL = await toDataURL(image); | |
return createImageElementFromDataURL(dataURL); | |
} | |
return createImageElementFromDataURL(image); | |
} | |
export interface CropOpts extends ImageOpts, CanvasOpts { | |
} | |
function disableImageSmoothing(context: CanvasRenderingContext2D) { | |
(<any> context).webkitImageSmoothingEnabled = false; | |
(<any> context).mozImageSmoothingEnabled = false; | |
context.imageSmoothingEnabled = false; | |
} | |
export async function crop(image: RawImageData, | |
rect: ILTRect, | |
opts: CropOpts = new DefaultImageOpts()): Promise<DataURL> { | |
const src = await createImageElement(image); | |
const canvas = opts.canvas || document.createElement("canvas"); | |
canvas.width = rect.width; | |
canvas.height = rect.height; | |
const ctx = canvas.getContext('2d', {alpha: false})!; | |
disableImageSmoothing(ctx); | |
ctx.drawImage(src, | |
rect.left, rect.top, rect.width, rect.height, | |
0, 0, rect.width, rect.height); | |
return canvas.toDataURL(); | |
} | |
export interface ResizeOpts extends ImageOpts, CanvasOpts { | |
} | |
export async function resize(data: RawImageData, | |
dimensions: IDimensions, | |
opts: ResizeOpts = new DefaultImageOpts()): Promise<ImageData> { | |
// There are two main ways to accomplish image scaling. | |
// | |
// Both involve creating a 'src' element which is an HTMLImageElement | |
// that contains our data. | |
// | |
// Then we have two options: | |
// | |
// 1. Call drawImage but set the width/height of the target much smaller | |
// so that when it's drawn you have the right dimensions. | |
// | |
// 2. Do something similar but then call scale() on the resulting image. | |
// | |
// This is essentially: | |
// | |
// <code> | |
// ctx.drawImage(src, 0, 0, image.width, image.height, | |
// 0, 0, image.width, image.height); | |
// | |
// const scaleX = dimensions.width / image.width; | |
// const scaleY = dimensions.height / image.height; | |
// | |
// ctx.scale(scaleX, scaleY); | |
// </code> | |
// | |
// ... but both strategies fail to work properly with clean smooth | |
// re-render so the result looks horrible. | |
const src = await createImageElement(data); | |
const tmpCanvas = opts.canvas || document.createElement("canvas"); | |
const ctx = tmpCanvas.getContext('2d', {alpha: false})!; | |
disableImageSmoothing(ctx); | |
tmpCanvas.width = dimensions.width; | |
tmpCanvas.height = dimensions.height; | |
ctx.drawImage(src, 0, 0, src.width, src.height, | |
0, 0, dimensions.width, dimensions.height); | |
return canvasToImageData(tmpCanvas, opts); | |
} | |
/** | |
* Extract image data from the given canvas directly and return it as an | |
* array buffer. | |
* @param canvas The canvas we should extract with. | |
* @param rect The rect within the given canvas | |
* @param opts The options for the image extraction | |
*/ | |
export async function extract(canvas: HTMLCanvasElement, | |
rect: ILTRect, | |
opts: ImageOpts = new DefaultImageOpts()): Promise<ImageData> { | |
Preconditions.assertPresent(canvas, "canvas"); | |
const xScale = canvas.width / canvas.offsetWidth; | |
const yScale = canvas.height / canvas.offsetHeight; | |
// scale the canvas rect to the actual width + height | |
// of the internal canvas. | |
const canvasRect = { | |
left: rect.left * xScale, | |
width: rect.width * xScale, | |
top: rect.top * yScale, | |
height: rect.height * yScale | |
}; | |
const tmpCanvas = document.createElement("canvas"); | |
const tmpCanvasCtx = tmpCanvas.getContext('2d', {alpha: false})!; | |
tmpCanvasCtx.imageSmoothingEnabled = false; | |
tmpCanvas.width = canvasRect.width; | |
tmpCanvas.height = canvasRect.height; | |
// copy data from the source canvas to the target | |
tmpCanvasCtx.drawImage(canvas, | |
canvasRect.left, canvasRect.top, canvasRect.width, canvasRect.height, | |
0, 0, canvasRect.width, canvasRect.height); | |
return await canvasToImageData(tmpCanvas, opts); | |
} | |
export async function canvasToImageData(canvas: HTMLCanvasElement, | |
opts: ImageOpts = new DefaultImageOpts()): Promise<ImageData> { | |
const data = await toArrayBuffer(canvas, opts); | |
return arrayBufferToImageData(data, {width: canvas.width, height: canvas.height}, opts.type); | |
} | |
export async function arrayBufferToImageData(data: ArrayBuffer, | |
dimensions: IDimensions, | |
type: ImageType): Promise<ImageData> { | |
return { | |
data, | |
format: 'arraybuffer', | |
...dimensions, | |
type | |
}; | |
} | |
} | |
export interface CanvasOpts { | |
canvas?: HTMLCanvasElement; | |
} | |
export interface ImageOpts { | |
readonly type: ImageType; | |
readonly quality: number; | |
} | |
export class DefaultImageOpts implements ImageOpts { | |
public readonly type = DEFAULT_IMAGE_TYPE; | |
public readonly quality = DEFAULT_IMAGE_QUALITY; | |
} |
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