自定义画笔 - 我想要两个渐变将它们链接在一起 [英] Custom Brush - I want two gradients chaining them together

问题描述

我正在制作条形图，我希望每个条形有两个单独的渐变.首先，我想要一个渐变，从上到下纯红色到透明红色.我想在上面绘制一个从右到左、黑色到不透明的渐变.

I am making a bar chart and I want two separate gradients for each bar. First I want a gradient to go from top to bottom solid red to transparent red. I want to paint over the top of that a gradient that goes from right to left, black to opaque.

所以 - 在左下角我们应该有;

So - In the bottom left we should have;

• 左下角 - Alpha 0
• 右下角 - Alpha 0
• 左上角 - Alpha 255 红色
• 右上角 - Alpha 255 颜色黑色

所以实际上我想采用纯色，向黑色添加从左到右的渐变，然后获取输出并添加从上到下的渐变到透明度.

So in effect I want to take a solid colour, add a left to right gradient to black then take the output of that and add a top to bottom gradient to transparency.

所有这一切，我希望它在一个画笔中，这甚至可能吗?

All this and I want it to be in a single brush, is this even possible?

推荐答案

是的.使用 VisualBrush 的 VisualBrush 来组合其他两个画笔.

Yes. Use a VisualBrush whose Visual is a Rectangle inside a Border to combine the other two brushes.

像这样:

<LinearGradientBrush x:Key="UnderBrush" EndPoint="0,1"> 
  <GradientStop Color="#FFFF0000" Offset="0" /> 
  <GradientStop Color="#00FF0000" Offset="1" /> 
</LinearGradientBrush> 

<LinearGradientBrush x:Key="OverBrush" EndPoint="1,0"> 
  <GradientStop Color="#00000000" Offset="0" /> 
  <GradientStop Color="#FF000000" Offset="1" /> 
</LinearGradientBrush> 

<VisualBrush x:Key="CombinedBrush">
  <VisualBrush.Visual>
    <Border Background="{StaticResource UnderBrush}">
      <Rectangle Fill="{StaticResource OverBrush}" Width="1" Height="1" />
    </Border>
  </VisualBrush.Visual>
</VisualBrush>

CombinedBrush 可用于绘制您的条形图，您将获得您所描述的效果.

CombinedBrush can be used to paint your bars, and you will get the effect you describe.

银光版

由于 Silverlight 没有 VisualBrush，因此您必须在代码中构建 WritableBitmap 并将其与 ImageBrush 一起使用:

Since Silverlight has no VisualBrush you must build a WritableBitmap in code and use it with an ImageBrush:

<ImageBrush x:Key="CombinedBrush">
  <my:VisualBrushSimulator.Visual>
    <Border Background="{StaticResource UnderBrush}">
      <Rectangle Fill="{StaticResource OverBrush}" Width="1" Height="1" />
    </Border>
  </my:VisualBrushSimulator.Visual>
</ImageBrush>

以下是 VisualBrushSimulator 的实现方式:

Here is how the VisualBrushSimulator might be implemented:

public class VisualBrushSimulator : DependencyObject
{
  public Visual GetVisual(DependencyObject obj) { return (Visual)obj.GetValue(VisualProperty); }
  public void SetVisual(DependencyObject obj, Visual value) { obj.SetValue(VisualProperty, value); }
  public static readonly DependencyProperty VisualProperty = DependencyProperty.RegisterAttached("Visual", typeof(Visual), typeof(VisualBrushSimulator), new PropertyMetadata
  {
    PropertyChangedCallback = (obj, e) =>
    {
      int width=1000;
      int height=1000;
      var bitmap = new WritableBitmap(width, height);
      bitmap.Render((Visual)e.NewValue, new ScaleTransform { ScaleX = width, ScaleY = height });
      ((ImageBrush)obj).ImageSource = bitmap;
    }
  });
}

请注意，这不是真正的 VisualBrush 模拟，因为对 Visual 的更改不会影响画笔.

Note that this is not a true VisualBrush simulation, since changes to the Visual do not affect the brush.

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