/**
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* project any angle onto the interval (-180;180]
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*/
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export function normalizeAngle(angle: number) {
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let a = angle;
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while (a > 0) a -= 360;
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return ((a - 180) % 360) + 180;
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}
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type SequenceItem = {
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frame: number;
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[k: string]: any;
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};
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/**
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* interpolate prop between two sequence items
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* @return {any} propValue
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* @example
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* interpolateProp({frame: 0, x: -10}, {frame: 100, x: 10}, 25, 'x'); // will return -5
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* @example
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* interpolateProp(
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* {frame: 0, rotation: -170},
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* {frame: 20, rotation: 170},
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* 5,
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* 'rotation'
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* ); // will return -175
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*/
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export const interpolateProp = (start: SequenceItem, end: SequenceItem, frame: number, prop: string): any => {
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// @todo edge cases
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const r = (frame - start.frame) / (end.frame - start.frame);
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// Interpolation of angles is more tricky due to the cyclical nature of the angle value.
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if (prop === "rotation") {
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// In order to perform interpolation over the shortest distance,
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// we must normalize the difference in the values of the angles to the interval of [180;180) degrees,
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// because this is analogous to [0;360) degrees,
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// but at the same time the maximum absolute value remains the minimum possible 180 degrees.
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const dAngle = normalizeAngle(end[prop] - start[prop]);
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return normalizeAngle(start[prop] + dAngle * r);
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}
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return start[prop] + (end[prop] - start[prop]) * r;
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};
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