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Image.js
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Image.js
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/**
* @module ol/Image
*/
import EventType from './events/EventType.js';
import ImageBase from './ImageBase.js';
import ImageState from './ImageState.js';
import {IMAGE_DECODE} from './has.js';
import {getHeight} from './extent.js';
import {listenOnce, unlistenByKey} from './events.js';
/**
* A function that takes an {@link module:ol/Image~ImageWrapper} for the image and a
* `{string}` for the src as arguments. It is supposed to make it so the
* underlying image {@link module:ol/Image~ImageWrapper#getImage} is assigned the
* content specified by the src. If not specified, the default is
*
* function(image, src) {
* image.getImage().src = src;
* }
*
* Providing a custom `imageLoadFunction` can be useful to load images with
* post requests or - in general - through XHR requests, where the src of the
* image element would be set to a data URI when the content is loaded.
*
* @typedef {function(ImageWrapper, string): void} LoadFunction
* @api
*/
class ImageWrapper extends ImageBase {
/**
* @param {import("./extent.js").Extent} extent Extent.
* @param {number|undefined} resolution Resolution.
* @param {number} pixelRatio Pixel ratio.
* @param {string} src Image source URI.
* @param {?string} crossOrigin Cross origin.
* @param {LoadFunction} imageLoadFunction Image load function.
*/
constructor(
extent,
resolution,
pixelRatio,
src,
crossOrigin,
imageLoadFunction
) {
super(extent, resolution, pixelRatio, ImageState.IDLE);
/**
* @private
* @type {string}
*/
this.src_ = src;
/**
* @private
* @type {HTMLCanvasElement|HTMLImageElement|HTMLVideoElement}
*/
this.image_ = new Image();
if (crossOrigin !== null) {
this.image_.crossOrigin = crossOrigin;
}
/**
* @private
* @type {?function():void}
*/
this.unlisten_ = null;
/**
* @protected
* @type {import("./ImageState.js").default}
*/
this.state = ImageState.IDLE;
/**
* @private
* @type {LoadFunction}
*/
this.imageLoadFunction_ = imageLoadFunction;
}
/**
* @return {HTMLCanvasElement|HTMLImageElement|HTMLVideoElement} Image.
* @api
*/
getImage() {
return this.image_;
}
/**
* Tracks loading or read errors.
*
* @private
*/
handleImageError_() {
this.state = ImageState.ERROR;
this.unlistenImage_();
this.changed();
}
/**
* Tracks successful image load.
*
* @private
*/
handleImageLoad_() {
if (this.resolution === undefined) {
this.resolution = getHeight(this.extent) / this.image_.height;
}
this.state = ImageState.LOADED;
this.unlistenImage_();
this.changed();
}
/**
* Load the image or retry if loading previously failed.
* Loading is taken care of by the tile queue, and calling this method is
* only needed for preloading or for reloading in case of an error.
* @api
*/
load() {
if (this.state == ImageState.IDLE || this.state == ImageState.ERROR) {
this.state = ImageState.LOADING;
this.changed();
this.imageLoadFunction_(this, this.src_);
this.unlisten_ = listenImage(
this.image_,
this.handleImageLoad_.bind(this),
this.handleImageError_.bind(this)
);
}
}
/**
* @param {HTMLCanvasElement|HTMLImageElement|HTMLVideoElement} image Image.
*/
setImage(image) {
this.image_ = image;
this.resolution = getHeight(this.extent) / this.image_.height;
}
/**
* Discards event handlers which listen for load completion or errors.
*
* @private
*/
unlistenImage_() {
if (this.unlisten_) {
this.unlisten_();
this.unlisten_ = null;
}
}
}
/**
* @param {HTMLCanvasElement|HTMLImageElement|HTMLVideoElement} image Image element.
* @param {function():any} loadHandler Load callback function.
* @param {function():any} errorHandler Error callback function.
* @return {function():void} Callback to stop listening.
*/
export function listenImage(image, loadHandler, errorHandler) {
const img = /** @type {HTMLImageElement} */ (image);
let listening = true;
let decoding = false;
let loaded = false;
const listenerKeys = [
listenOnce(img, EventType.LOAD, function () {
loaded = true;
if (!decoding) {
loadHandler();
}
}),
];
if (img.src && IMAGE_DECODE) {
decoding = true;
img
.decode()
.then(function () {
if (listening) {
loadHandler();
}
})
.catch(function (error) {
if (listening) {
if (loaded) {
loadHandler();
} else {
errorHandler();
}
}
});
} else {
listenerKeys.push(listenOnce(img, EventType.ERROR, errorHandler));
}
return function unlisten() {
listening = false;
listenerKeys.forEach(unlistenByKey);
};
}
export default ImageWrapper;