public static Color GetRelativeColor(this GradientStopCollection gsc, double offset, float alpha)
{
var point = gsc.SingleOrDefault(x => x.Offset == offset);
if (point != null)
{
return(point.Color);
}
GradientStop before = gsc.Where(x => x.Offset == gsc.Min(m => m.Offset)).First();
GradientStop after = gsc.Where(x => x.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.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);
if (alpha >= 0 && alpha <= 1)
{
color.ScA = alpha;
}
else
{
color.ScA = (float)((offset - before.Offset) * (after.Color.ScA - before.Color.ScA) / (after.Offset - before.Offset) + before.Color.ScA);
}
return(color);
}