Question

I have the following GradientStopCollection:

GradientStopCollection grsc = new GradientStopCollection(3);
grsc.Add(new GradientStop(Colors.Red, 0));
grsc.Add(new GradientStop(Colors.Yellow, .5));
grsc.Add(new GradientStop(Colors.Green, 1));

Can I get the color at a specific “location”?
For example:

• Location 0: Red
• Location .5: Yellow
• Location .75: Yellow<~>Green

Is there an API in WPF / some third party library that could do that?

Answer 1

To get a color at a specific point is necessary to understand the gradient in question, and this is not the role of class GradientStopCollection. The concept of this class is not to understand a gradient, but should be a simple collection of support to a gradient.

Is important that you understand the concept of each class.

To get a color, you need to instantiate a class that represents a gradient using the gradient to paint and finally get their color from the painting.

but I’ll give you a quicker solution. You can use a gradient algorithm to generate a single point. This is an implementation of how to do this using a linear gradient algorithm:

public static class GradientStopCollectionExtensions
{
    public static Color GetRelativeColor(this GradientStopCollection gsc, double offset)
    {
        var point = gsc.SingleOrDefault(f => f.Offset == offset);
        if (point != null) return point.Color;

        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;
    }
}

PS: This algorithm assumes there are no stops with the same offset. If there are multiple stops with the same offset a InvalidOperationException will be thrown.

Add this class in your current context (namespace context)

To get your color in any place you insert something like this:

var color = grsc.GetRelativeColor(.75);