使用LinearGradientBrush的FillPath

Question

我在这个主题GDI+ .NET: LinearGradientBrush wider than 202 pixels causes color wrap-around中发现了类似的问题，但解决方案对我不起作用。我也不能在这个话题中提问。请看一下。下面是我的代码：

public partial class Form1 : Form {

    int ShadowThick = 10;
    Color ShadowColor = Color.Gray;
    int width;
    int height;

    public Form1() {
        InitializeComponent();
        width = this.Width - 100;
        height = this.Height - 100;
    }

    private void Form1_Paint(object sender, PaintEventArgs e) {
        //e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
        GraphicsPath shadowPath = new GraphicsPath();
        LinearGradientBrush shadowBrush = null;
        // draw vertical shadow
        shadowPath.AddArc(this.width - this.ShadowThick, this.ShadowThick, this.ShadowThick,
            this.ShadowThick, 180, 180);
        shadowPath.AddLine(this.width, this.ShadowThick * 2, this.width,
            this.height - this.ShadowThick);
        shadowPath.AddLine(this.width, this.height - this.ShadowThick,
            this.width - this.ShadowThick, this.height - this.ShadowThick);
        shadowPath.CloseFigure();
        // declare the brush
        shadowBrush = new LinearGradientBrush(PointF.Empty,
            new PointF(this.ShadowThick + 1, 0), this.ShadowColor, Color.Transparent);
        //shadowBrush = new LinearGradientBrush(PointF.Empty,
        //    new PointF(this.ShadowThick + 1, 0), this.ShadowColor, Color.Transparent);

        //e.Graphics.DrawPath(Pens.Black, shadowPath);

        e.Graphics.PixelOffsetMode = PixelOffsetMode.Half;
        e.Graphics.FillPath(shadowBrush, shadowPath);
    }

}

我希望从左到右从暗到亮，但请看：

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我试着画一个阴影，我坚持这样做。

Answer 1

正如Hans在下面评论的那样，笔刷坐标需要与路径匹配，所以不是这样：

shadowBrush = new LinearGradientBrush(PointF.Empty,
    new PointF(this.ShadowThick + 1, 0), this.ShadowColor, Color.Transparent);

它应该是：

new LinearGradientBrush(new Point(this.width - this.ShadowThick, 0),
                        new Point(this.width, 0),
                        this.ShadowColor, Color.Transparent);

此外，您还应该处理您创建的图形对象。我还更改了你的画笔，只使用Point而不是PointF，因为你不需要处理浮点数。

以下是重写的代码：

  e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
  e.Graphics.PixelOffsetMode = PixelOffsetMode.Half;
  using (GraphicsPath shadowPath = new GraphicsPath()) {
    shadowPath.StartFigure();
    shadowPath.AddArc(this.width - this.ShadowThick, this.ShadowThick, 
        this.ShadowThick, this.ShadowThick, 180, 180);
    shadowPath.AddLine(this.width, this.ShadowThick * 2, this.width,
        this.height - this.ShadowThick);
    shadowPath.AddLine(this.width, this.height - this.ShadowThick,
        this.width - this.ShadowThick, this.height - this.ShadowThick);
    shadowPath.CloseFigure();
    using (var shadowBrush = new LinearGradientBrush(
        new Point(this.width - this.ShadowThick, 0),
        new Point(this.width, 0),
        this.ShadowColor, Color.Transparent)) {
      e.Graphics.FillPath(shadowBrush, shadowPath);
    }
  }