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:
Yellow<~>Green
Is there an API in WPF
/ some third party library that could do that?
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);
I've tried the method written by Jonny Piazzi. But it didn't work correctly.
So I write my own one below:
private static Color GetColorByOffset(GradientStopCollection collection, double offset)
{
GradientStop[] stops = collection.OrderBy(x => x.Offset).ToArray();
if (offset <= 0) return stops[0].Color;
if (offset >= 1) return stops[stops.Length - 1].Color;
GradientStop left = stops[0], right = null;
foreach (GradientStop stop in stops)
{
if (stop.Offset >= offset)
{
right = stop;
break;
}
left = stop;
}
Debug.Assert(right != null);
offset = Math.Round((offset - left.Offset)/(right.Offset - left.Offset), 2);
byte a = (byte) ((right.Color.A - left.Color.A)*offset + left.Color.A);
byte r = (byte) ((right.Color.R - left.Color.R)*offset + left.Color.R);
byte g = (byte) ((right.Color.G - left.Color.G)*offset + left.Color.G);
byte b = (byte) ((right.Color.B - left.Color.B)*offset + left.Color.B);
return Color.FromArgb(a, r, g, b);
}
I hope it works for you!
I've used this method in my xaml code below to show a specified number as heat map position.
<LinearGradientBrush x:Key="CountBrush" StartPoint="0 0" EndPoint="1 0">
<GradientStop Offset="0.00" Color="ForestGreen"/>
<GradientStop Offset="0.50" Color="Yellow"/>
<GradientStop Offset="1.00" Color="OrangeRed"/>
</LinearGradientBrush>
<local:Int32ToColorConverter x:Key="CountToColorConverter" Min="0" Max="200" LinearBrush="{StaticResource CountBrush}"/>
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