How to read the color from an offset of a XAML LinearGradientBrush?

Question

Given a LinearGradientBrush defined as follows:

        <LinearGradientBrush x:Key="RedYellowGradient">
            <GradientStop Color="Blue" Offset="0.01" />
            <GradientStop Color="Purple" Offset="0.25"/>
            <GradientStop Color="Red" Offset="0.5"/>
            <GradientStop Color="Orange" Offset="0.75"/>
            <GradientStop Color="Yellow" Offset="1.0"/>
        </LinearGradientBrush>

What is required to take that definition and determine the color represented by a specific offset, such as 0.13 or 0.82 without rendering anything visible?

This would take the form of a function with a prototype something like this:

Function GetColorFromBrushOffset(br as LinearGradientBrush, offset as Single) as SomeColorDataStructure

What would need to go in the function body? I'm not looking for finished code (though I won't refuse it!) just some ideas about what data structures and system calls to use.

Possessive

Just access the Gradientstops, and interpolate between each pairs ([0]->[1], [1]->[2] etc.) offset, now use the interpolated value to interpolate between each pairs color. – Vue

this might be helpful, possible duplicate – Urinate

@JohanLarsson You're right; the code in one of the answers looks correct for my purposes. I'd rather reproduce it here than mark this duplicate, since I couldn't find that question from my searches, and his question is different in scope. – Possessive

Maybe ask the guy to answer this q also? I tested his code and upvoted his answer in place. – Urinate

Same here; I also submitted edits to the tags to make it easier to find. The Roslyn translator did a near perfect job of rendering his C# into the VB I needed. I'll remove the self-answer if he comes over. – Possessive

Answer 1

This class (from one of this question's answers by @JonnyPiazzi) appears to exactly address my question:

public static class GradientStopCollectionExtensions
{
    public static Color GetRelativeColor(this GradientStopCollection gsc, double offset)
    {
        GradientStop before = gsc.Where(w => w.Offset == gsc.Min(m => m.Offset)).First();
        GradientStop after = gsc.Where(w => w.Offset == gsc.Max(m => m.Offset)).First();

        foreach (var gs in gsc)
        {
            if (gs.Offset < offset && gs.Offset > before.Offset)
            {
                before = gs;
            }
            if (gs.Offset > offset && gs.Offset < after.Offset)
            {
                after = gs;
            }
        }

        var color = new Color();

        color.ScA = (float)((offset - before.Offset) * (after.Color.ScA - before.Color.ScA) / (after.Offset - before.Offset) + before.Color.ScA);
        color.ScR = (float)((offset - before.Offset) * (after.Color.ScR - before.Color.ScR) / (after.Offset - before.Offset) + before.Color.ScR);
        color.ScG = (float)((offset - before.Offset) * (after.Color.ScG - before.Color.ScG) / (after.Offset - before.Offset) + before.Color.ScG);
        color.ScB = (float)((offset - before.Offset) * (after.Color.ScB - before.Color.ScB) / (after.Offset - before.Offset) + before.Color.ScB);

        return color;
    }
}

Possessive