Skia to System.Numerics Port Question

SkiaPort.md

I'm attempting to translate some code from Skia and I'm not sure exactly how SkMatrix works

https://github.com/google/skia/blob/1f193df9b393d50da39570dab77a0bb5d28ec8ef/src/core/SkPathBuilder.cpp#L459-L483

SkMatrix pointTransform;
pointTransform.setRotate(-angle);

SkPoint transformedMidPoint;
pointTransform.mapPoints(&transformedMidPoint, &midPointDistance, 1);
SkScalar squareRx = rx * rx;
SkScalar squareRy = ry * ry;
SkScalar squareX = transformedMidPoint.fX * transformedMidPoint.fX;
SkScalar squareY = transformedMidPoint.fY * transformedMidPoint.fY;

// Check if the radii are big enough to draw the arc, scale radii if not.
// http://www.w3.org/TR/SVG/implnote.html#ArcCorrectionOutOfRangeRadii
SkScalar radiiScale = squareX / squareRx + squareY / squareRy;
if (radiiScale > 1) {
    radiiScale = SkScalarSqrt(radiiScale);
    rx *= radiiScale;
    ry *= radiiScale;
}

pointTransform.setScale(1 / rx, 1 / ry);
pointTransform.preRotate(-angle);

SkPoint unitPts[2];
pointTransform.mapPoints(unitPts, srcPts, (int) SK_ARRAY_COUNT(unitPts));
SkVector delta = unitPts[1] - unitPts[0];

I'm trying to figure out what the equivalent of transforms would be that are applied to the matrix using System.Numerics.

• setRotate
• setScale
• preRotate

Would the following be accurate?

static float DegToRad(float deg) => deg * (MathF.PI / 180f);

// setRotate ? 
Matrix3x2 pointTransform = Matrix3x2.CreateRotation(DegToRad(-angle));

// setScale ?
pointTransform.M11 = 1 / rx;
pointTransform.M22 = 1 / ry;

// preRotate ?
pointTransform *= Matrix3x2.CreateRotation(DegToRad(-angle));