I'm trying to draw a windows theme element (the window close button, specifically) to an image, and whenever I do, the image has ragged non-transparent bits. I got this code from a sample that didn't do this (it was all owner-drawn, mine draws to an image.) Any idea why it won't draw with full transparency?

Bitmap output = new Bitmap(closeButton.Width, closeButton.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
Graphics fx = Graphics.FromImage(output);
      
IntPtr hTheme = OpenThemeData (Handle, "Window");
         
Rectangle rClose = new Rectangle(0, 0, closeButton.Width, closeButton.Height);
RECT reClose = rClose;
RECT reClip = reClose;
IntPtr hDC = fx.GetHdc();
DrawThemeBackground (hTheme, hDC, WP_CLOSEBUTTON, state, ref reClose, ref reClip);
fx.ReleaseHdc (hDC);
fx.DrawImage(output,rClose);
CloseThemeData (hTheme);
fx.Dispose();

No ideas why this wouldn't draw the element transparently?

This works perfectly for me.
What are you doing with the output Bitmap?

Well, I was assigning it to a PictureBox (I'm trying to fake a themed close button). I also called Save on it so I could check it out as a PNG, but the image is non-transparent there too.

A clarification - the image I get is index-transparent, but not alpha transparent. There are little bits that are transparent, but none of the pixels on the edge are half-transparent.  

Control windows don't support alpha transparency. You need to either use graphical components, all drawn on a single control, or use windows with alpha transparency -- they cannot be child windows.

Regards,
Frank Hileman

check out VG.net: http://www.vgdotnet.com
Animated vector graphics system
Integrated Visual Studio .NET graphics editor

Yes, I've tried that, but it didn't help. See, I'm not drawing to a control, I'm drawing to a bitmap - it seems that this should be pretty simple in that case, right?

 

if (IsThemeBackgroundPartiallyTransparent(_hTheme, BP_PUSHBUTTON, _iStateId))   {     DrawThemeParentBackground(_hwnd, hdcPaint, prcPaint);   }   DrawThemeBackground(_hTheme,                     hdcPaint,                     BP_PUSHBUTTON,                     _iStateId,                     &rcClient,                     prcPaint);

That is the MSDN sample. If IsThemeBackgroundPartiallyTransparent returns false, there is no alpha blending -- that is the correct behavior.

I think that explains why the button looks so oogly as well You may need your own close button if you want something better.

When I use that code, I still get the same result - all the alpha-blended bits are drawn onto gray, and only the fully-transparent bits are transparent. And I set a breakpoint - IsThemeBackgroundPartiallyTransparent is returning true.

This is weird because the code I took this from (which did all its drawing itself, in WmPaint), does not have this problem - it is able to draw the same button nicely alpha-blended. The only difference is that I draw to a Bitmap.

I don't see any code clearing your bitmap to transparent alpha.

fx.Clear(Color.Transparent);

I just tried that out (Yeah, I forgot about this thread and gave up) and it still doesn't work...

Bitmap output = new Bitmap(closeButton.Width, closeButton.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
            Graphics fx = Graphics.FromImage(output);
           

            IntPtr hTheme = OpenThemeData (Handle, "Window");
           
            if (hTheme == IntPtr.Zero)
            {
                fx.Dispose();
                return drawLegacyCloseButton (state);
            }

            Rectangle rClose = new Rectangle(0, 0, closeButton.Width, closeButton.Height);
            RECT reClose = rClose;
            RECT reClip = reClose; // should fx.VisibleClipBounds be used here?
           
            fx.Clear(Color.Transparent);
            IntPtr hDC = fx.GetHdc();
            if (IsThemeBackgroundPartiallyTransparent(hTheme, WP_CLOSEBUTTON, state) != 0)
            {
                DrawThemeParentBackground(this.Handle, hDC, ref reClose);
            }
            DrawThemeBackground (hTheme, hDC, WP_CLOSEBUTTON, state, ref reClose, ref reClip);
            fx.ReleaseHdc (hDC);
            fx.DrawImage(output,rClose);
            CloseThemeData (hTheme);
            fx.Dispose();

            output.Save("close" + state.ToString() + ".png");

            return output;

Still works perfectly for me although I did change the code very slightly.

Rectangle and RECT are not interchangeable.

struct RECT
{
  public int Left, Top, Right, Bottom;
  public RECT(int l, int t, int r, int b)
  {
    Left = l;
    Top = t;
    Right = r;
    Bottom = b;
  }
  public RECT(Rectangle r)
  {
    Left = r.Left;
    Top = r.Top;
    Right = r.Right;
    Bottom = r.Bottom;
  }
  public Rectangle ToRectangle()
  {
    return Rectangle.FromLTRB(Left, Top, Right, Bottom);
  }
}

Rectangle rClose = new Rectangle(0, 0, closeButton.Width, closeButton.Height);
RECT reClose = new RECT(rClose);

Although Format32bppArgb does work for me, the format should really be Format32bppPArgb.