/**
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* Creates a {@link createBillboardPointCallback.CanvasFunction} that will create a canvas with a point.
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*
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* @param {Number} centerAlpha The alpha of the center of the point. The value must be in the range [0.0, 1.0].
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* @param {String} cssColor The CSS color string.
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* @param {String} cssOutlineColor The CSS color of the point outline.
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* @param {Number} cssOutlineWidth The width of the outline in pixels.
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* @param {Number} pixelSize The size of the point in pixels.
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* @return {createBillboardPointCallback.CanvasFunction} The function that will return a canvas with the point drawn on it.
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*
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* @private
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*/
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function createBillboardPointCallback(
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centerAlpha,
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cssColor,
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cssOutlineColor,
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cssOutlineWidth,
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pixelSize
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) {
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return function () {
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var canvas = document.createElement("canvas");
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var length = pixelSize + 2 * cssOutlineWidth;
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canvas.height = canvas.width = length;
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var context2D = canvas.getContext("2d");
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context2D.clearRect(0, 0, length, length);
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if (cssOutlineWidth !== 0) {
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context2D.beginPath();
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context2D.arc(length / 2, length / 2, length / 2, 0, 2 * Math.PI, true);
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context2D.closePath();
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context2D.fillStyle = cssOutlineColor;
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context2D.fill();
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// Punch a hole in the center if needed.
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if (centerAlpha < 1.0) {
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context2D.save();
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context2D.globalCompositeOperation = "destination-out";
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context2D.beginPath();
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context2D.arc(
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length / 2,
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length / 2,
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pixelSize / 2,
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0,
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2 * Math.PI,
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true
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);
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context2D.closePath();
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context2D.fillStyle = "black";
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context2D.fill();
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context2D.restore();
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}
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}
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context2D.beginPath();
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context2D.arc(length / 2, length / 2, pixelSize / 2, 0, 2 * Math.PI, true);
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context2D.closePath();
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context2D.fillStyle = cssColor;
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context2D.fill();
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return canvas;
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};
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}
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/**
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* A function that returns a canvas containing an image of a point.
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* @callback createBillboardPointCallback.CanvasFunction
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* @returns {HTMLCanvasElement} The result of the calculation.
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*/
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export default createBillboardPointCallback;
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