Add VideoSensing math module

- 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
This commit is contained in:
Michael "Z" Goddard 2018-03-30 14:51:47 -04:00
parent b46c956203
commit a32b15a8f9
No known key found for this signature in database
GPG key ID: 762CD40DD5349872

View file

@ -0,0 +1,76 @@
/**
* A constant value helping to transform a value in radians to degrees.
* @type {number}
*/
const TO_DEGREE = 180 / Math.PI;
/**
* A object reused to save on memory allocation returning u and v vector from
* motionVector.
* @type {UV}
*/
const _motionVectorOut = {u: 0, v: 0};
/**
* Determine a motion vector combinations of the color component difference on
* the x axis, y axis, and temporal axis.
* @param {number} A2 - a sum of x axis squared
* @param {number} A1B2 - a sum of x axis times y axis
* @param {number} B1 - a sum of y axis squared
* @param {number} C2 - a sum of x axis times temporal axis
* @param {number} C1 - a sum of y axis times temporal axis
* @param {UV} out - optional object to store return UV info in
* @returns {UV} a uv vector representing the motion for the given input
*/
const motionVector = function (A2, A1B2, B1, C2, C1, out = _motionVectorOut) {
// Compare sums of X * Y and sums of X squared and Y squared.
const delta = ((A1B2 * A1B2) - (A2 * B1));
if (delta) {
// System is not singular - solving by Kramer method.
const deltaX = -((C1 * A1B2) - (C2 * B1));
const deltaY = -((A1B2 * C2) - (A2 * C1));
const Idelta = 8 / delta;
out.u = deltaX * Idelta;
out.v = deltaY * Idelta;
} else {
// Singular system - find optical flow in gradient direction.
const Norm = ((A1B2 + A2) * (A1B2 + A2)) + ((B1 + A1B2) * (B1 + A1B2));
if (Norm) {
const IGradNorm = 8 / Norm;
const temp = -(C1 + C2) * IGradNorm;
out.u = (A1B2 + A2) * temp;
out.v = (B1 + A1B2) * temp;
} else {
out.u = 0;
out.v = 0;
}
}
return out;
};
/**
* Translate an angle in degrees with the range -180 to 180 rotated to
* Scratch's reference angle.
* @param {number} degrees - angle in range -180 to 180
* @returns {number} angle from Scratch's reference angle
*/
const scratchDegrees = function (degrees) {
return ((degrees + 270) % 360) - 180;
};
/**
* Get the angle of the y and x component of a 2d vector in degrees in
* Scratch's coordinate plane.
* @param {number} y - the y component of a 2d vector
* @param {number} x - the x component of a 2d vector
* @returns {number} angle in degrees in Scratch's coordinate plane
*/
const scratchAtan2 = function (y, x) {
return scratchDegrees(Math.atan2(y, x) * TO_DEGREE);
};
module.exports = {
motionVector,
scratchDegrees,
scratchAtan2
};