System.Drawing.Drawing2D.Matrix.Transform*(ReadOnlySpan) methods mutate the ReadOnlySpan #15226

Background and motivation

The System.Drawing.Drawing2D.Matrix.TransformPoints and TransformVectors methods are intended to transform the array of values in-place, and that's clearly what the code is doing. The T[] overloads even call the ReadOnlySpan overloads to do the work. But because of the mutation, the span overloads should take Spans, not ReadOnlySpans.

It may also be worth doing a sweep through System.Drawing to see if anything else was transcribed incorrectly like this.

I'm seeing this in .NET 10 and .NET 11-rc1. I don't know when these APIs were originally added.

API Proposal

namespace System.Drawing.Drawing2D;

public sealed class Matrix
{
    // Remove or mark [Obsolete("Use the Span overloads", true)]
    // Also add [EditorBrowsable(EditorBrowsableState.Never)]
    public void TransformPoints(params ReadOnlySpan<PointF> pts);
    public void TransformPoints(params ReadOnlySpan<Point> pts);
    public void TransformVectors(params ReadOnlySpan<PointF> pts);
    public void TransformVectors(params ReadOnlySpan<Point> pts);

    // Add these, and also tag with [OverloadResolutionPriority(1)] if not deleting the ReadOnlySpan overloads
    public void TransformPoints(params Span<PointF> pts);
    public void TransformPoints(params Span<Point> pts);
    public void TransformVectors(params Span<PointF> pts);
    public void TransformVectors(params Span<Point> pts);
}

API Usage

APIs would be consumed in the same way they are today. I'm guessing most uses are going through the array overloads or via implicit cast to ReadOnlySpan from arrays or mutable Spans.

Alternative Designs

No response

Risks

Removing the methods risks breaking any code that was using them. At compile time it may be fine, but it will definitely break binary compatibility.

Will this feature affect UI controls?

No