【WPF】打造Blend风格的BrushPicker（1）

在贴出来上一篇文章后，感觉那个ColorPicker太简单了，于是决定搞个Blend中的那种ColorPicker。由于工作量比较大，所以打算分成几次来完成。

  

首先说明一下，这个Demo还是属于未完成的阶段，比如ColorPicker的属性只是简单地设置了一个SelectedColor属性，而实际上分为A,R,G,B四个属性比较合适，这样可以在右边直接修改值；又比如，样式实在是很难看……（太累了，明天再说吧……）不过整体来看，还是能说明问题了。

【分析】

    Blend中的ColorPicker其实应该分为好几个部分。首先是中间那个彩条状选择基色的Bar。我称之为ColorRainbowBar。然后是左侧基于给定的基色精确调节颜色的Box。我称之为ColorAdjuster。

    这两个控件都是基于偏移量（Offset）来确定颜色的，因此，我首先定义了一个基类ColorBoxBase来提供偏移量，以及通过鼠标点击和拖拽改变偏移量的逻辑。

【控件的实现】

ColorBoxBase

    这个是颜色选择器的基础。他提供了偏移量属性和鼠标事件改变偏移量的逻辑。

    public class ColorBoxBase : Control
    {
        #region HorizontalOffset

        /// <summary>
        /// Gets HorizontalOffset
        /// </summary>
        public double HorizontalOffset
        {
            get { return (double)GetValue(HorizontalOffsetProperty); }
            protected set { SetValue(HorizontalOffsetPropertyKey, value); }
        }

        // Using a DependencyProperty as the backing store for HorizontalOffset.  This enables animation, styling, binding, etc
        private static readonly DependencyPropertyKey HorizontalOffsetPropertyKey = DependencyProperty.RegisterReadOnly(
            "HorizontalOffset",
            typeof(double),
            typeof(ColorBoxBase),
            new FrameworkPropertyMetadata(0.0, OnHorizontalOffsetChanged, OnCoerceHorizontalOffset));

        public static readonly DependencyProperty HorizontalOffsetProperty = HorizontalOffsetPropertyKey.DependencyProperty;

        private static void OnHorizontalOffsetChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            ColorBoxBase box = sender as ColorBoxBase;
            if (box != null)
            {
                box.OnHorizontalOffsetChanged((double)e.OldValue, (double)e.NewValue);
            }
        }

        private static object OnCoerceHorizontalOffset(DependencyObject sender, object value)
        {
            ColorBoxBase box = sender as ColorBoxBase;
            if (box != null)
            {
                double x = (double)value;

                if (x < 0)
                    x = 0;
                else if (x > box.ActualWidth)
                    x = box.ActualWidth;
                return x;
            }
            return value;
        }

        #endregion

        #region VerticalOffset

        /// <summary>
        /// Gets VerticalOffset
        /// </summary>
        public double VerticalOffset
        {
            get { return (double)GetValue(VerticalOffsetProperty); }
            protected set { SetValue(VerticalOffsetPropertyKey, value); }
        }

        // Using a DependencyProperty as the backing store for VerticalOffsett.  This enables animation, styling, binding, etc
        private static readonly DependencyPropertyKey VerticalOffsetPropertyKey = DependencyProperty.RegisterReadOnly(
            "VerticalOffset",
            typeof(double),
            typeof(ColorBoxBase),
            new FrameworkPropertyMetadata(0.0, OnVerticalOffsetChanged, OnCoerceVerticalOffset));

        public static readonly DependencyProperty VerticalOffsetProperty = VerticalOffsetPropertyKey.DependencyProperty;

        private static void OnVerticalOffsetChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            ColorBoxBase box = sender as ColorBoxBase;
            if (box != null)
            {
                box.OnVerticalOffsetChanged((double)e.OldValue, (double)e.NewValue);
            }
        }

        private static object OnCoerceVerticalOffset(DependencyObject sender, object value)
        {
            ColorBoxBase box = sender as ColorBoxBase;
            if (box != null)
            {
                double y = (double)value;

                if (y < 0)
                    y = 0;
                else if (y > box.ActualHeight)
                    y = box.ActualHeight;
                return y;
            }
            return value;
        }

        #endregion       

        #region SelectedColor

        /// <summary>
        /// Gets/Sets SelectedColor
        /// </summary>
        public Color SelectedColor
        {
            get { return (Color)GetValue(SelectedColorProperty); }
            set { SetValue(SelectedColorProperty, value); }
        }

        private static readonly DependencyProperty SelectedColorProperty = DependencyProperty.Register(
            "SelectedColor",
            typeof(Color),
            typeof(ColorBoxBase),
            new FrameworkPropertyMetadata(Colors.Red, OnSelectedColorChanged));

        private static void OnSelectedColorChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            ColorBoxBase box = sender as ColorBoxBase;
            if (box != null)
            {
                box.OnSelectedColorChanged(e);
                box.RaiseEvent(new ColorChangedEventArgs(SelectedColorChangedEvent, box, (Color)e.OldValue, (Color)e.NewValue));
            }
        }

        #endregion

        #region SelectedColorChangedEvent

        public static RoutedEvent SelectedColorChangedEvent =
            EventManager.RegisterRoutedEvent("SelectedColorChanged", RoutingStrategy.Bubble, typeof(ColorChangedEventHandler), typeof(ColorBoxBase));

        public event ColorChangedEventHandler SelectedColorChanged
        {
            add { AddHandler(SelectedColorChangedEvent, value); }
            remove { RemoveHandler(SelectedColorChangedEvent, value); }
        }

        #endregion
        
        #region Methods for override

        protected virtual void OnHorizontalOffsetChanged(double oldValue, double newValue)
        {
            //
        }

        protected virtual void OnVerticalOffsetChanged(double oldValue, double newValue)
        {
            //
        }

        protected virtual void OnSelectedColorChanged(DependencyPropertyChangedEventArgs e)
        {

        }

        #endregion

        #region "Drag" the pointer

        protected override void OnRenderSizeChanged(SizeChangedInfo sizeInfo)
        {
            base.OnRenderSizeChanged(sizeInfo);

            double previousHeight = sizeInfo.PreviousSize.Height;
            double ratio = this.VerticalOffset / previousHeight;
            this.VerticalOffset = sizeInfo.NewSize.Height * ratio;

            double previousWidth = sizeInfo.PreviousSize.Width;
            ratio = this.HorizontalOffset / previousWidth;
            this.HorizontalOffset = sizeInfo.NewSize.Width * ratio;
        }

        protected override void OnPreviewMouseLeftButtonDown(MouseButtonEventArgs e)
        {
            base.OnPreviewMouseLeftButtonDown(e);

            this.HorizontalOffset = e.GetPosition(this).X;
            this.VerticalOffset = e.GetPosition(this).Y;

            if (!this.IsMouseCaptured)
            {
                this.CaptureMouse();
            }
        }

        protected override void OnPreviewMouseMove(MouseEventArgs e)
        {
            base.OnPreviewMouseMove(e);
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                this.HorizontalOffset = e.GetPosition(this).X;
                this.VerticalOffset = e.GetPosition(this).Y;
            }
        }

        protected override void OnPreviewMouseLeftButtonUp(MouseButtonEventArgs e)
        {
            base.OnPreviewMouseLeftButtonUp(e);
            if (this.IsMouseCaptured)
            {
                this.ReleaseMouseCapture();
            }
        }

        #endregion
    }

    代码有点长，但是大部分都是在定义依赖属性。注意，其中的HorizontalOffset和VerticalOffset都是只读属性。并且，实际上的“拖拽”逻辑并不直接去控制UI，而仅仅是改变了Offset，这种思路是WPF里面很常见的。稍后我们就会看到如何在模板里面通过绑定来实现拖拽的效果。

ColorRainbowBar

    ColorRainbowBar由ColorBoxBase继承而来，比较有意思的是它的背景色，其实是一个有7个GradientStop的LinearGradientBrush

    <LinearGradientBrush x:Key="ColorRainbowBarBrush" StartPoint="0,0" EndPoint="0 1">
        <GradientStop Color="#FFFF0000" Offset="0.0"/>
        <GradientStop Color="#FFFFFF00" Offset="0.166"/>
        <GradientStop Color="#FF00FF00" Offset="0.333"/>
        <GradientStop Color="#FF00FFFF" Offset="0.5"/>
        <GradientStop Color="#FF0000FF" Offset="0.666"/>
        <GradientStop Color="#FFFF00FF" Offset="0.833"/>
        <GradientStop Color="#FFFF0000" Offset="1.0"/>
    </LinearGradientBrush>

    其中，最主要的地方是根据Offset来确定颜色的代码。主要的原理在注释中写的比较清楚了。

       // 在位移变化时重新构建颜色
        protected override void OnVerticalOffsetChanged(double oldValue, double newValue)
        {
            //////////////////////////////////////////////////////////////////
            // 0: R:255  G:0     B:0         0 / 3 --- 0, 0  
            // 1: R:255  G:255   B:0         1 / 3 --- 0, 1      0  +1   0
            // 2: R:0    G:255   B:0         2 / 3 --- 0, 2     -1   0   0
            // 3: R:0    G:255   B:255       3 / 3 --- 1, 0      0   0  +1
            // 4: R:0    G:0     B:255       4 / 3 --- 1, 1      0  -1   0
            // 5: R:255  G:0     B:255       5 / 3 --- 1, 2     +1   0   0
            // 6: R:255  G:0     B:0         6 / 3 --- 2, 0      0   0  -1
            //////////////////////////////////////////////////////////////////

            // 计算总的颜色数
            // 一共6个区间
            int totalCount = 256 * 6;
            // 计算颜色的位置偏移
            int colorOffset = (int)(this.VerticalOffset / this.ActualHeight * totalCount);
            if (colorOffset < 0)
            {
                colorOffset = 0;
            }
            else if (colorOffset > totalCount)
            {
                colorOffset = totalCount;
            }

            // 计算属于哪个区间
            int offsetBase = colorOffset / 256;
            // 计算相对于该区间的偏移
            int relativeOffset = colorOffset - 256 * offsetBase;

            byte a = 255;
            byte r = 0, g = 0, b = 0;
            int dr = 0, dg = 0, db = 0;

            // 设置各个区间的数据
            switch (offsetBase)
            {
                case 0:
                    r = 255;
                    g = 0;
                    b = 0;
                    dg = +1;
                    break;
                case 1:
                    r = 255;
                    g = 255;
                    b = 0;
                    dr = -1;
                    break;
                case 2:
                    r = 0;
                    g = 255;
                    b = 0;
                    db = +1;
                    break;
                case 3:
                    r = 0;
                    g = 255;
                    b = 255;
                    dg = -1;
                    break;
                case 4:
                    r = 0;
                    g = 0;
                    b = 255;
                    dr = +1;
                    break;
                case 5:
                    r = 255;
                    g = 0;
                    b = 255;
                    db = -1;
                    break;
                case 6:
                    r = 255;
                    g = 0;
                    b = 0;
                    break;
                default:
                    r = 255;
                    g = 0;
                    b = 0;
                    break;
            }

            // 构建颜色
            r += (byte)(relativeOffset * dr);
            g += (byte)(relativeOffset * dg);
            b += (byte)(relativeOffset * db);

            this.SelectedColor = Color.FromArgb(a, r, g, b);
        }

    首先我们要根据偏移量算出属于哪个区间，然后算出相对于该区间的偏移量，接着根据最前面注释中的表中的分析，确定每个颜色的改变方向（FF还是00）。最后计算颜色。

    它的模板如下： 

    <Style TargetType="{x:Type local:ColorRainbowBar}">
        <Setter Property="Background" Value="{StaticResource ColorRainbowBarBrush}"/>
        <Setter Property="Foreground" Value="#FFC4C4C4"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:ColorRainbowBar}">
                    <Border Background="{TemplateBinding Background}" 
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <Canvas x:Name="ThumbHolder" ClipToBounds="True">
                            <Thumb x:Name="Thumb" Height="4" Width="{Binding ElementName=ThumbHolder, Path=ActualWidth}"
                                   Canvas.Top="{TemplateBinding VerticalOffset}"
                                   Style="{StaticResource ColorRainbowBarPointerThumbStyle}"/>
                        </Canvas>                        
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    注意，里面放了个Thumb，但我却没有写任何拖拽的逻辑，只是简单的绑定到Offset而已。这样当我们用鼠标拖拽的时候，感觉上就是在拖拽这个Thumb了。

ColorAdjuster

    ColorAdjuster比较麻烦，一个是它的颜色，并不是简单的LinearGradientBrush，而是包含了两个方向（水平和垂直）的复杂渐变。为了解决这个问题，我放置了两个Rectangle，一个在水平方向渐变填充，一个在垂直方向渐变填充。然后两者的颜色合成为最终的效果。需要特别注意的是，必须把LinearGradientBrush的ColorInterpolationMode设置为ScRgbLinearInterpolation，否则你会发现颜色叠加之后，中间有一条混合带的颜色特别明显。 

另外，我将它的背景色固定为White，这个也算是讨巧了。因为两个方向的渐变均是渐变到透明，如果背景色不是白色的话，会跟控件下面的颜色发生混淆，影像颜色的效果。

    <Style TargetType="{x:Type local:ColorAdjuster}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:ColorAdjuster}">
                    <Border Background="White"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <Grid>
                            <Rectangle x:Name="HorizontalColor">
                                <Rectangle.Fill>
                                    <LinearGradientBrush StartPoint="1,0.5" EndPoint="0,0.5" ColorInterpolationMode="ScRgbLinearInterpolation">
                                        <GradientStop Color="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=BaseColor}" Offset="0"/>
                                        <GradientStop Color="#00000000" Offset="1"/>                                          
                                    </LinearGradientBrush>
                                </Rectangle.Fill>
                            </Rectangle>
                            <Rectangle x:Name="VerticalColor">
                                <Rectangle.Fill>
                                    <LinearGradientBrush StartPoint="0.5,1" EndPoint="0.5,0" ColorInterpolationMode="ScRgbLinearInterpolation">
                                        <GradientStop Color="#FF000000" Offset="0"/>
                                        <GradientStop Color="#00000000" Offset="1"/>
                                    </LinearGradientBrush>
                                </Rectangle.Fill>
                            </Rectangle>
                            <Canvas ClipToBounds="True">
                                <Thumb x:Name="Thumb" Height="10" Width="10"
                                       Canvas.Left="{TemplateBinding HorizontalOffset}"
                                       Canvas.Top="{TemplateBinding VerticalOffset}"
                                       Style="{StaticResource ColorAdjusterPointerThumbStyle}"/>
                            </Canvas>
                        </Grid>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

让我费了费脑子的是颜色的算法。为此，我专门画了一个图来分析。

    颜色的变化其实是一个F(x,y)的形式，跟水平和垂直的偏移量都有关系。同时计算其实比较难想，于是我把计算过程拆成步：首先计算水平偏移后的结果，接着水平偏移结果的基础上，接着计算垂直偏移。

        private void CreateColor()
        {
            Color baseColor = this.BaseColor;
            double xRatio = 1.0 - this.HorizontalOffset / this.ActualWidth;
            double yRatio = 1.0 - this.VerticalOffset / this.ActualHeight;

            // 计算差量
            // 首先是X方向差量，然后以此为基准，计算Y方向差量
            byte currentR = (byte)(baseColor.R + (255 - baseColor.R) * xRatio);
            currentR = (byte)(currentR * yRatio);

            byte currentG = (byte)(baseColor.G + (255 - baseColor.G) * xRatio);
            currentG = (byte)(currentG * yRatio);

            byte currentB = (byte)(baseColor.B + (255 - baseColor.B) * xRatio);
            currentB = (byte)(currentB * yRatio);

            this.SelectedColor = Color.FromArgb(255, currentR, currentG, currentB);
        }

ColorPicker

    最后的工作就是把前面做的控件组合起来，做一个ColorPicker。我这里使用的是CustomControl，但其实UserControl也没什么问题。

我原来的打算是做一个SolidColorBrushPicker，一个GradientBrushPicker，可以直接返回Brush，但今天实在太累了，也就凑合着做了个ColorPicker，主要是为了测试一下。明天开始继续进军BrushPicker。

它没什么代码，就是一个模板。

    <Style TargetType="{x:Type local:ColorPicker}">
        <Setter Property="Background" Value="Gray"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:ColorPicker}">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <DockPanel Margin="4">
                            <Grid DockPanel.Dock="Right" Width="100">
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="24"/>
                                    <RowDefinition Height="24"/>
                                    <RowDefinition Height="24"/>
                                    <RowDefinition Height="24"/>
                                    <RowDefinition Height="*"/>
                                </Grid.RowDefinitions>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="24"/>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>
                                <TextBlock Grid.Row="0" Grid.Column="0" Text="R" VerticalAlignment="Center"/>
                                <TextBlock Grid.Row="1" Grid.Column="0" Text="G" VerticalAlignment="Center"/>
                                <TextBlock Grid.Row="2" Grid.Column="0" Text="B" VerticalAlignment="Center"/>
                                <TextBlock Grid.Row="3" Grid.Column="0" Text="A" VerticalAlignment="Center"/>
                                <Border Grid.Row="0" Grid.Column="1"
                                        BorderBrush="Gray" BorderThickness="1" Background="Red">
                                    <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" 
                                               Text="{Binding ElementName=Adjuster, Path=SelectedColor.R}"/>
                                </Border>
                                <Border Grid.Row="1" Grid.Column="1"
                                        BorderBrush="Gray" BorderThickness="1" Background="Green">
                                    <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" 
                                               Text="{Binding ElementName=Adjuster, Path=SelectedColor.G}"/>
                                </Border>
                                <Border Grid.Row="2" Grid.Column="1"
                                        BorderBrush="Gray" BorderThickness="1" Background="Blue">
                                    <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" 
                                               Text="{Binding ElementName=Adjuster, Path=SelectedColor.B}"/>
                                </Border>
                                <Border Grid.Row="3" Grid.Column="1"
                                        BorderBrush="Gray" BorderThickness="1" Background="Red">
                                    <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" 
                                               Text="{Binding ElementName=Adjuster, Path=SelectedColor.A}"/>
                                </Border>
                            </Grid>
                            <DockPanel>
                                <local:ColorRainbowBar x:Name="RainbowBar" DockPanel.Dock="Right" Width="20"/>
                                <local:ColorAdjuster x:Name="Adjuster" 
                                                     BaseColor="{Binding ElementName=RainbowBar, Path=SelectedColor}"
                                                     SelectedColor="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=SelectedColor, Mode=TwoWay}"/>
                            </DockPanel>
                        </DockPanel>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

【下篇预告】

    好了，其实到此为止，我们需要攻坚的两个东东，ColorRainbowBar和ColorAdjuster已经完成了，剩下的任务就是把选出的Color转换成需要的Brush，下一篇里我打算讲讲怎么搞个SolidColorBrushPicker出来，如果快的话，估计GradientBrushPicker也能出来:)

注：我的开发环境是Vista SP1 + .Net 3.5 SP1 + VS2008 SP1

代码下载https://files.cnblogs.com/RMay/ColorPickerSeries/RMay.Demos.rar