BilinearGradientBrushExtension, custom brush in WPF using MarkupExtension instead

WPF的类库现在锁死不让继承实现自定义的Brush,因为基类的brush含有抽象而且是internal的一些函数，像internal abstract System.Windows.Media.Composition.DUCE.ResourceHandle AddRefOnChannelCore(System.Windows.Media.Composition.DUCE.Channel channel)，就没法继承实现，而且一般的DrawingBrush, ImageBrush都是sealed。而我这次需要一个相当于2维的GradientBrush一样的东西来实现传入一个颜色矩阵，画出一副ColorMap的东西。因为直接从brush继承设置想直接从imagesource继承都不可能，只好用MarkupExtension的方法绕：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Markup;
using System.Windows.Media.Imaging;
using System.Windows.Media;
using System.Windows;
using System.Windows.Media.Animation;
using System.ComponentModel;


    [MarkupExtensionReturnType(typeof(Brush))]
    class BilinearGradientBrushExtension:MarkupExtension,INotifyPropertyChanged
    {
        List<Color> colorMatrix = new List<Color>();
        int countX, countY;

        private void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged != null)
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public List<Color> ColorMatrix
        {
            get { return colorMatrix; }
            set { colorMatrix = value ; OnPropertyChanged("ColorMatrix"); }
        }

        public int CountY
        {
            get { return countY; }
            set { countY = value; }
        }

        public int CountX
        {
            get { return countX; }
            set { countX = value; }
        }

        public override object ProvideValue(IServiceProvider serviceProvider)
        {

            int i = ColorMatrix.Count;

            int[] pixelValues = GeneratePixelValues();

            WriteableBitmap bmp = new WriteableBitmap(countX, countY, 96, 96, PixelFormats.Pbgra32, null);
            bmp.WritePixels(new Int32Rect(0, 0, countX, countY), pixelValues, pixelValues.Length, 0);
            
            ImageBrush brush = new ImageBrush(bmp);

            return brush;
        }

        private int[] GeneratePixelValues()
        {
            int pixelCount = countX * countY;

            int[] pixelValues = new int[pixelCount];
            for (int i = 0; i < countY; i++)
            {
                for (int j = 0; j < countX; j++)
                {
                    Color c = ColorMatrix[i * countY + j];
                    byte a = (byte)c.A;
                    byte r = (byte)c.R;
                    byte g = (byte)c.G;
                    byte b = (byte)c.B;

                    pixelValues[i*countY +j] = (a << 24) + (r << 16) + (g << 8) + b;
                }
            }
            return pixelValues;
        }


        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }

对应的xaml：

<l:BilinearGradientBrushExtension x:Name="contur" CountX="2" CountY="2">
       <l:BilinearGradientBrushExtension.ColorMatrix>
                <Color A="100" R="255" G="0" B="0" />
                <Color A="100" R="0" G="255" B="0" />
                 <Color A="100" R="155" G="155" B="155" />
                 <Color A="100" R="0" G="0" B="255" />
        </l:BilinearGradientBrushExtension.ColorMatrix>
</l:BilinearGradientBrushExtension>

 

产生的图片：

不过使用MarkupExtension的方法有个问题，就是产生的图像是静态的，颜色没办法在运行时改变，而且不能使用DependencyProperty，我试过INotifyProperty，会抛异常，暂时没有其他方法。