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https://github.com/scratchfoundation/scratch-vm.git
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a32b15a8f9
- motionVector takes motion component and returns a 2d vector - scratchAtan2 takes a y and x value and returns an angle in degrees referencing Scratch's coordinate system
76 lines
2.5 KiB
JavaScript
76 lines
2.5 KiB
JavaScript
/**
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* A constant value helping to transform a value in radians to degrees.
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* @type {number}
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*/
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const TO_DEGREE = 180 / Math.PI;
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/**
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* A object reused to save on memory allocation returning u and v vector from
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* motionVector.
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* @type {UV}
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*/
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const _motionVectorOut = {u: 0, v: 0};
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/**
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* Determine a motion vector combinations of the color component difference on
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* the x axis, y axis, and temporal axis.
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* @param {number} A2 - a sum of x axis squared
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* @param {number} A1B2 - a sum of x axis times y axis
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* @param {number} B1 - a sum of y axis squared
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* @param {number} C2 - a sum of x axis times temporal axis
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* @param {number} C1 - a sum of y axis times temporal axis
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* @param {UV} out - optional object to store return UV info in
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* @returns {UV} a uv vector representing the motion for the given input
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*/
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const motionVector = function (A2, A1B2, B1, C2, C1, out = _motionVectorOut) {
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// Compare sums of X * Y and sums of X squared and Y squared.
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const delta = ((A1B2 * A1B2) - (A2 * B1));
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if (delta) {
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// System is not singular - solving by Kramer method.
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const deltaX = -((C1 * A1B2) - (C2 * B1));
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const deltaY = -((A1B2 * C2) - (A2 * C1));
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const Idelta = 8 / delta;
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out.u = deltaX * Idelta;
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out.v = deltaY * Idelta;
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} else {
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// Singular system - find optical flow in gradient direction.
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const Norm = ((A1B2 + A2) * (A1B2 + A2)) + ((B1 + A1B2) * (B1 + A1B2));
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if (Norm) {
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const IGradNorm = 8 / Norm;
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const temp = -(C1 + C2) * IGradNorm;
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out.u = (A1B2 + A2) * temp;
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out.v = (B1 + A1B2) * temp;
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} else {
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out.u = 0;
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out.v = 0;
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}
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}
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return out;
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};
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/**
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* Translate an angle in degrees with the range -180 to 180 rotated to
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* Scratch's reference angle.
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* @param {number} degrees - angle in range -180 to 180
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* @returns {number} angle from Scratch's reference angle
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*/
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const scratchDegrees = function (degrees) {
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return ((degrees + 270) % 360) - 180;
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};
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/**
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* Get the angle of the y and x component of a 2d vector in degrees in
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* Scratch's coordinate plane.
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* @param {number} y - the y component of a 2d vector
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* @param {number} x - the x component of a 2d vector
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* @returns {number} angle in degrees in Scratch's coordinate plane
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*/
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const scratchAtan2 = function (y, x) {
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return scratchDegrees(Math.atan2(y, x) * TO_DEGREE);
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};
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module.exports = {
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motionVector,
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scratchDegrees,
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scratchAtan2
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};
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