src/utils/perspective.js

// Extracted from perspective-transform npm package
// Translated to pure ES Module

function round(num){
    return Math.round(num*10000000000)/10000000000;
}

function getNormalizationCoefficients(srcPts, dstPts, isInverse){
    if(isInverse){
        var tmp = dstPts;
        dstPts = srcPts;
        srcPts = tmp;
    }
    var r1 = [srcPts[0], srcPts[1], 1, 0, 0, 0, -1*dstPts[0]*srcPts[0], -1*dstPts[0]*srcPts[1]];
    var r2 = [0, 0, 0, srcPts[0], srcPts[1], 1, -1*dstPts[1]*srcPts[0], -1*dstPts[1]*srcPts[1]];
    var r3 = [srcPts[2], srcPts[3], 1, 0, 0, 0, -1*dstPts[2]*srcPts[2], -1*dstPts[2]*srcPts[3]];
    var r4 = [0, 0, 0, srcPts[2], srcPts[3], 1, -1*dstPts[3]*srcPts[2], -1*dstPts[3]*srcPts[3]];
    var r5 = [srcPts[4], srcPts[5], 1, 0, 0, 0, -1*dstPts[4]*srcPts[4], -1*dstPts[4]*srcPts[5]];
    var r6 = [0, 0, 0, srcPts[4], srcPts[5], 1, -1*dstPts[5]*srcPts[4], -1*dstPts[5]*srcPts[5]];
    var r7 = [srcPts[6], srcPts[7], 1, 0, 0, 0, -1*dstPts[6]*srcPts[6], -1*dstPts[6]*srcPts[7]];
    var r8 = [0, 0, 0, srcPts[6], srcPts[7], 1, -1*dstPts[7]*srcPts[6], -1*dstPts[7]*srcPts[7]];

    var matA = [r1, r2, r3, r4, r5, r6, r7, r8];
    var matB = dstPts;
    var matC;

    try{
        let AT = window.math.transpose(matA);
        let ATA = window.math.multiply(AT, matA);
        matC = window.math.inv(ATA);
    }catch(e){
        console.log(e);
        return [1,0,0,0,1,0,0,0];
    }

    var matD = window.math.multiply(matC, window.math.transpose(matA));
    var matX = window.math.multiply(matD, matB);
    for(var i = 0; i < matX.length; i++) {
        matX[i] = round(matX[i]);
    }
    matX[8] = 1;

    return matX;
}

export class PerspT {
    constructor(srcPts, dstPts){
        this.srcPts = srcPts;
        this.dstPts = dstPts;
        this.coeffs = getNormalizationCoefficients(this.srcPts, this.dstPts, false);
        this.coeffsInv = getNormalizationCoefficients(this.srcPts, this.dstPts, true);
    }

    transform(x,y) {
        var coordinates = [];
        coordinates[0] = (this.coeffs[0]*x + this.coeffs[1]*y + this.coeffs[2]) / (this.coeffs[6]*x + this.coeffs[7]*y + 1);
        coordinates[1] = (this.coeffs[3]*x + this.coeffs[4]*y + this.coeffs[5]) / (this.coeffs[6]*x + this.coeffs[7]*y + 1);
        return coordinates;
    }

    transformInverse(x,y) {
        var coordinates = [];
        coordinates[0] = (this.coeffsInv[0]*x + this.coeffsInv[1]*y + this.coeffsInv[2]) / (this.coeffsInv[6]*x + this.coeffsInv[7]*y + 1);
        coordinates[1] = (this.coeffsInv[3]*x + this.coeffsInv[4]*y + this.coeffsInv[5]) / (this.coeffsInv[6]*x + this.coeffsInv[7]*y + 1);
        return coordinates;
    }
}

export default function perspective(srcPts, dstPts) {
    return new PerspT(srcPts, dstPts);
}