mirror of
https://github.com/photonstorm/phaser
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36 lines
1,007 B
JavaScript
36 lines
1,007 B
JavaScript
/**
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* Convert a distance along this curve into a `time` value which will be between 0 and 1.
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*
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* For example if this curve has a length of 100 pixels then `findT(50)` would return `0.5`.
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*
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* @param {integer} distance - The distance into the curve in pixels. Should be a positive integer.
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* @return {number} The time (`t`) value, a float between 0 and 1.
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*/
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var FindT = function (curve, distance)
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{
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if (distance <= 0)
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{
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return 0;
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}
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// Find the _points which bracket the distance value
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var ti = Math.floor(distance / curve.length * curve._accuracy);
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while (ti > 0 && curve._points[ti] > distance)
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{
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ti--;
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}
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while (ti < curve._accuracy && curve._points[ti] < distance)
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{
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ti++;
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}
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// Linear interpolation to get a more accurate fix
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var dt = curve._points[ti] - curve._points[ti - 1];
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var d = distance - curve._points[ti - 1];
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return ((ti - 1) / curve._accuracy) + d / (dt * curve._accuracy);
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};
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module.exports = FindT;
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