utils.ts

export function vecAdd(vecOne: Array<number>, vecTwo: Array<number>){
    let vecSum: Array<number> = vecOne;

    vecSum[0] += vecTwo[0];
    vecSum[1] += vecTwo[1];
    vecSum[2] += vecTwo[2];

    return vecSum;
}

export function vecSubtract(vecOne: Array<number>, vecTwo: Array<number>){
    let vecSubt: Array<number> = vecOne;

    vecSubt[0] -= vecTwo[0];
    vecSubt[1] -= vecTwo[1];
    vecSubt[2] -= vecTwo[2];

    return vecSubt;
}

export function vecMultiply(vecOne: Array<number>, factor: number){
    vecOne[0] *= factor;
    vecOne[1] *= factor;
    vecOne[2] *= factor;

    return vecOne;
}

export function vecLength(vec: Array<number>){
    let length: number;
    length = Math.sqrt(vec[0]*vec[0] + vec[1]*vec[1] + vec[2]*vec[2]);
    return length;
}

export function vecNormalize(vec: Array<number>){
    let computedLength = vecLength(vec);
    if(computedLength == 0){computedLength = 1};

    let inverse = 1 / computedLength;

    let normalized: Array<number> = new Array;

    normalized[0] = vec[0] * inverse;
    normalized[1] = vec[1] * inverse;
    normalized[2] = vec[2] * inverse;

    return normalized;
}

export function vecDotProduct(vecOne: Array<number>, vecTwo: Array<number>){
    let dotProduct = vecOne[0]*vecTwo[0] + vecOne[1]*vecTwo[1] + vecOne[2]*vecTwo[2];
    return dotProduct;
}

export function vecAngle(vecOne: Array<number>, vecTwo: Array<number>){
    //calculate radiant
    let radiant = Math.acos(vecDotProduct(vecOne, vecTwo) / (vecLength(vecOne) * vecLength(vecTwo)))

    //convert into degrees
    let degrees = radiant * 180 / Math.PI;
    return degrees;
}

export function vecCrossProduct(vecOne: Array<number>, vecTwo: Array<number>){
    let crossProduct : Array<number> = new Array;

    crossProduct[0] = vecOne[1]*vecTwo[2] - vecOne[2]*vecTwo[1];
    crossProduct[1] = vecOne[2]*vecTwo[0] - vecOne[0]*vecTwo[2];
    crossProduct[2] = vecOne[0]*vecTwo[1] - vecOne[1]*vecTwo[0];

    return crossProduct;
}

export function matrixProduct(a: Array<number>, b: Array<number>){
    // for 3x3 matrix only
    //[
    //    0 1 2
    //    3 4 5
    //    6 7 8
    //  ]
    return [
        //row 1
        a[0]*b[0] + a[1]*b[3] + a[2]*b[6], a[0]*b[1] + a[1]*b[4] + a[2]*b[7], a[0]*b[2] + a[1]*b[5] + a[2]*b[8],
        //row 2
        a[3]*b[0] + a[4]*b[3] + a[5]*b[6], a[3]*b[1] + a[4]*b[4] + a[5]*b[7], a[3]*b[2] + a[4]*b[5] + a[5]*b[8],
        //row 3
        a[6]*b[0] + a[7]*b[3] + a[8]*b[6], a[6]*b[1] + a[7]*b[4] + a[8]*b[7], a[6]*b[2] + a[7]*b[5] + a[8]*b[8]
    ]
}

export function multVecMatrix(v: Array<number>, m: Array<number>){
    return [
        v[0]*m[0] + v[1]*m[3] + v[2]*m[6], v[0]*m[1] + v[1]*m[4] + v[2]*m[7], v[0]*m[2] + v[1]*m[5] + v[2]*m[8]
    ]
}

export function rotX(degrees: number){
    const radian = degrees * Math.PI / 180
    return [
        1, 0, 0,
        0, Math.cos(radian), Math.sin(radian),
        0, -1*Math.sin(radian), Math.cos(radian)
    ]
}

export function rotY(degrees: number){
    const radian = degrees * Math.PI / 180
    return [
        Math.cos(radian), 0, -1*Math.sin(radian),
        0, 1, 0,
        Math.sin(radian), 0, Math.cos(radian)
    ]
}

export function rotZ(degrees: number){
    const radian = degrees * Math.PI / 180
    return [
        Math.cos(radian), Math.sin(radian), 0,
        -1*Math.sin(radian), Math.cos(radian), 0,
        0, 0, 1
    ]
}
//