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55 lines
1.7 KiB
JavaScript
55 lines
1.7 KiB
JavaScript
import defined from "../Core/defined.js";
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/**
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* A policy for discarding tile images that contain no data (and so aren't actually images).
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* This policy discards {@link DiscardEmptyTileImagePolicy.EMPTY_IMAGE}, which is
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* expected to be used in place of any empty tile images by the image loading code.
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*
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* @alias DiscardEmptyTileImagePolicy
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* @constructor
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*
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* @see DiscardMissingTileImagePolicy
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*/
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function DiscardEmptyTileImagePolicy(options) {}
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/**
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* Determines if the discard policy is ready to process images.
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* @returns {Boolean} True if the discard policy is ready to process images; otherwise, false.
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*/
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DiscardEmptyTileImagePolicy.prototype.isReady = function () {
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return true;
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};
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/**
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* Given a tile image, decide whether to discard that image.
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*
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* @param {HTMLImageElement} image An image to test.
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* @returns {Boolean} True if the image should be discarded; otherwise, false.
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*/
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DiscardEmptyTileImagePolicy.prototype.shouldDiscardImage = function (image) {
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return DiscardEmptyTileImagePolicy.EMPTY_IMAGE === image;
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};
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var emptyImage;
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Object.defineProperties(DiscardEmptyTileImagePolicy, {
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/**
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* Default value for representing an empty image.
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* @type {HTMLImageElement}
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* @readonly
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* @memberof DiscardEmptyTileImagePolicy
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*/
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EMPTY_IMAGE: {
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get: function () {
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if (!defined(emptyImage)) {
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emptyImage = new Image();
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// load a blank data URI with a 1x1 transparent pixel.
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emptyImage.src =
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"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=";
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}
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return emptyImage;
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},
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},
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});
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export default DiscardEmptyTileImagePolicy;
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