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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | 1x 2x 1x 1x 3x 1x 1x 3x | import defined from "../Core/defined.js";
/**
* A policy for discarding tile images that contain no data (and so aren't actually images).
* This policy discards {@link DiscardEmptyTileImagePolicy.EMPTY_IMAGE}, which is
* expected to be used in place of any empty tile images by the image loading code.
*
* @alias DiscardEmptyTileImagePolicy
* @constructor
*
* @see DiscardMissingTileImagePolicy
*/
function DiscardEmptyTileImagePolicy(options) {}
/**
* Determines if the discard policy is ready to process images.
* @returns {boolean} True if the discard policy is ready to process images; otherwise, false.
*/
DiscardEmptyTileImagePolicy.prototype.isReady = function () {
return true;
};
/**
* Given a tile image, decide whether to discard that image.
*
* @param {HTMLImageElement} image An image to test.
* @returns {boolean} True if the image should be discarded; otherwise, false.
*/
DiscardEmptyTileImagePolicy.prototype.shouldDiscardImage = function (image) {
return DiscardEmptyTileImagePolicy.EMPTY_IMAGE === image;
};
let emptyImage;
Object.defineProperties(DiscardEmptyTileImagePolicy, {
/**
* Default value for representing an empty image.
* @type {HTMLImageElement}
* @readonly
* @memberof DiscardEmptyTileImagePolicy
*/
EMPTY_IMAGE: {
get: function () {
if (!defined(emptyImage)) {
emptyImage = new Image();
// load a blank data URI with a 1x1 transparent pixel.
emptyImage.src =
"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=";
}
return emptyImage;
},
},
});
export default DiscardEmptyTileImagePolicy;
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