在 WinApi 中使用 C# 笔和画笔？

Question

如何从Brush 获得HBRUSH 和从Pen 获得HPEN？
我想知道这两者之间有什么联系吗？

（我想使用 .NET's System.Drawing 中未实现的 WinApi 函数，例如 DrawRoundRect/CreateRoundRectRgn，并且我想使用 .NET 中的画笔，而不是自己创建它们。）

Answer 1

Brush 类确实有一个名为 nativeBrush 的私​​有字段，它将 HBRUSH 句柄保存为 IntPtr。

因为它是一个私有字段，它可能会随着对 .Net 的任何修订而改变，但如果你不介意使用一些狡猾、脆弱的反射来获得它的价值，你可以做一些像这样令人讨厌的事情：

Brush brush = ...the brush that you want to get at the handle for
FieldInfo field = typeof(Brush).GetField("nativeBrush",BindingFlags.NonPublic|BindingFlags.Instance);
IntPtr hbrush = (IntPtr)field.GetValue(brush);

Pen 有一个类似的字段nativePen，您可以使用类似的反射代码访问它。

但是，如果您可以使用上面 Don 所示的 GraphicsPath，那么风险会小得多。

也可以查看this article on creating rounded rectangles using GraphicsPath

Answer 2

我不再有原始来源，甚至可能是一个 SO 项目。无论如何，这是我使用的不久前有人提供的课程：

/// <summary>
/// Collection of often-used classes and methods for easy access.
/// </summary>
public class RoundedDrawing
{
    private static GraphicsPath GetRoundedRectanglePath(Int32 x, Int32 y, Int32 width, Int32 height, Int32 radius)
    {
        GraphicsPath path = new GraphicsPath();
        path.AddLine(x + radius, y, x + width - radius, y);
        if (radius > 0)
            path.AddArc(x + width - 2 * radius, y, 2 * radius, 2 * radius, 270.0f, 90.0f);
        path.AddLine(x + width, y + radius, x + width, y + height - radius);
        if (radius > 0)
            path.AddArc(x + width - 2 * radius, y + height - 2 * radius, 2 * radius, 2 * radius, 0.0f, 90.0f);
        path.AddLine(x + width - radius, y + height, x + radius, y + height);
        if (radius > 0)
            path.AddArc(x, y + height - 2 * radius, 2 * radius, 2 * radius, 90.0f, 90.0f);
        path.AddLine(x, y + height - radius, x, y + radius);
        if (radius > 0)
            path.AddArc(x, y, 2 * radius, 2 * radius, 180.0f, 90.0f);
        return path;
    }

    /// <summary>
    /// Fills the interior of a rounded rectangle.
    /// </summary>
    public static void FillRoundedRectangle(Graphics graphics, Brush brush, float x, float y, float width, float height, float radius)
    {
        FillRoundedRectangle(graphics, brush, (Int32)x, (Int32)y, (Int32)width, (Int32)height, (Int32)radius);
    }

    /// <summary>
    /// Fills the interior of a rounded rectangle.
    /// </summary>
    public static void FillRoundedRectangle(Graphics graphics, Brush brush, Rectangle rect, Int32 radius)
    {
        FillRoundedRectangle(graphics, brush, rect.Left, rect.Top, rect.Width, rect.Height, radius);
    }

    /// <summary>
    /// Fills the interior of a rounded rectangle.
    /// </summary>
    public static void FillRoundedRectangle(Graphics graphics, Brush brush, RectangleF rect, float radius)
    {
        FillRoundedRectangle(graphics, brush, (Int32)rect.Left, (Int32)rect.Top, (Int32)rect.Width, (Int32)rect.Height, (Int32)radius);
    }

    /// <summary>
    /// Fills the interior of a rounded rectangle.
    /// </summary>
    public static void FillRoundedRectangle(Graphics graphics, Brush brush, Int32 x, Int32 y, Int32 width, Int32 height, Int32 radius)
    {
        using (GraphicsPath path = GetRoundedRectanglePath(x, y, width, height, radius))
            graphics.FillPath(brush, path);
    }

    /// <summary>
    /// Draws the outline of a rounded rectangle.
    /// </summary>
    public static void DrawRoundedRectangle(Graphics graphics, Pen pen, float x, float y, float width, float height, float radius)
    {
        DrawRoundedRectangle(graphics, pen, (Int32)x, (Int32)y, (Int32)width, (Int32)height, (Int32)radius);
    }

    /// <summary>
    /// Draws the outline of a rounded rectangle.
    /// </summary>
    public static void DrawRoundedRectangle(Graphics graphics, Pen pen, Rectangle rect, Int32 radius)
    {
        DrawRoundedRectangle(graphics, pen, rect.Left, rect.Top, rect.Width, rect.Height, radius);
    }

    /// <summary>
    /// Draws the outline of a rounded rectangle.
    /// </summary>
    public static void DrawRoundedRectangle(Graphics graphics, Pen pen, RectangleF rect, float radius)
    {
        DrawRoundedRectangle(graphics, pen, (Int32)rect.Left, (Int32)rect.Top, (Int32)rect.Width, (Int32)rect.Height, (Int32)radius);
    }

    /// <summary>
    /// Draws the outline of a rounded rectangle.
    /// </summary>
    public static void DrawRoundedRectangle(Graphics graphics, Pen pen, Int32 x, Int32 y, Int32 width, Int32 height, Int32 radius)
    {
        using (GraphicsPath path = GetRoundedRectanglePath(x, y, width, height, radius))
            graphics.DrawPath(pen, path);
    }
}

只需在您收到Graphics 对象的任何Paint 或PaintBackground 事件中进行调用。将它与其他任何东西一起传递，并绘制圆形的东西。

可以选择将其全部保存在 .NET 中，无需外部 P/Invokes。