CreatePatternBrush / Ellipse not working on WinMobile device but on emulator

Question

To draw a circular part of a bitmap on the screen, I use a PatternBrush created from the bitmap to fill an ellipse. I use P/Invoke to the native functions because there seems to be a bug in CF2.0 if you use the managed functions (see here for more details: http://social.msdn.microsoft.com/forums/en-US/netfxcompact/thread/e831ea2f-039a-4b92-adb6-941954bee060/).

Here is the code I use:

[DllImport("coredll.dll")]
private extern static int Ellipse(IntPtr hdc, int nLeftRect, int nTopRect, int nRightRect, int nBottomRect);

[DllImport("coredll.dll")]
private extern static IntPtr CreatePatternBrush(IntPtr hImage);

[DllImport("coredll.dll")]
private extern static IntPtr CreatePen(int fnPenStyle, int nWidth, uint crColor);

[DllImport("coredll.dll")]
private extern static IntPtr SelectObject(IntPtr hDC, IntPtr hBrush);

[DllImport("coredll.dll")]
private extern static bool DeleteObject(IntPtr hBrush);

private void DrawCircleOfBitmap(Graphics g, Bitmap bmp, Rectangle rect)
{
    IntPtr hBitmap = bmp.GetHbitmap();  // get HBitmap
    IntPtr hBrush = CreatePatternBrush(hBitmap); // create the PatternBrush
    IntPtr hPen = CreatePen(5, 1, 0);   // empty Pen (PS_NULL = 5)
    IntPtr hDC = g.GetHdc();   // get HDC
    IntPtr hOldBrush = SelectObject(hDC, hBrush); // select Brush into context
    IntPtr hOldPen = SelectObject(hDC, hPen); // select Pen into context
    Ellipse(hDC, rect.Left, rect.Top, rect.Right, rect.Bottom);
    // Release of native GDI objects
    SelectObject(hDC, hOldBrush);
    SelectObject(hDC, hOldPen);
    DeleteObject(hBrush);
    DeleteObject(hPen);
    g.ReleaseHdc(hDC);
    DeleteObject(hBitmap);
}

This works perfect on every emulator (WM6, WM6.1.4, WM6.5), but if I use exactly the same on my real device (HTC Tytn II) all I get is a white circle. The circle is not filled with the bitmap. I checked the return codes of every line on the device - everything reports no error. Replacing CreatePatternBrush with CreateSolidBrush works, than it fills the circle with a color. Anybody an idea why the pattern brush is not working?

Thanks Maik

Answer 1

Based on the behavior, it's very likely that the display driver for the Tytn II doesn't support the pattern brush. It probably should tell GDI that it's not supported, but it's not. This is not unusual though - very often OEMs will not implement every feature for the display driver (alpha blending being a classic example) and not have the driver report it as unsupported.