用指定颜色填充一个闭合区域

using System.Runtime.InteropServices;

[DllImport("gdi32.dll")]
public static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);
[DllImport("gdi32.dll")]
public static extern IntPtr CreateSolidBrush(int crColor);
[DllImport("gdi32.dll")]
public static extern bool ExtFloodFill(IntPtr hdc, int nXStart, int nYStart,
int crColor, uint fuFillType);
[DllImport("gdi32.dll")]
public static extern bool DeleteObject(IntPtr hObject);
[DllImport("gdi32.dll")]
public static extern int GetPixel(IntPtr hdc, int x, int y);
public static uint FLOODFILLBORDER = 0;
public static uint FLOODFILLSURFACE = 1;

private void button1_Click(object sender, EventArgs e)
{
Graphics vGraphics = Graphics.FromHwnd(Handle);
vGraphics.DrawRectangle(Pens.Blue, new Rectangle(0, 0, 300, 300));
vGraphics.DrawRectangle(Pens.Blue, new Rectangle(50, 70, 300, 300));
IntPtr vDC = vGraphics.GetHdc();
IntPtr vBrush = CreateSolidBrush(ColorTranslator.ToWin32(Color.Red));
IntPtr vPreviouseBrush = SelectObject(vDC, vBrush);
ExtFloodFill(vDC, 10, 10, GetPixel(vDC, 10, 10), FLOODFILLSURFACE);
SelectObject(vDC, vPreviouseBrush);
DeleteObject(vBrush);
vGraphics.ReleaseHdc(vDC);
}