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WindowsCE.[Essential Windows CE Application Programming].Jon Wiley & Son.zip

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<B>Essential Windows CE Application Programming</B>
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<I>(Publisher: John Wiley & Sons, Inc.)</I>
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Author(s): Robert Burdick
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ISBN: 0471327476
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Publication Date: 03/01/99
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<!--TITLE=Essential Windows CE Application Programming//-->
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<!--CHAPTER=9//-->
<!--PAGES=269-272//-->
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<P>You can see how telling Windows CE that you erased your window background when you really didn&#146;t can cause problems. Incorrectly returning a non-zero value in response to WM_ERASEBKGND can prevent the proper background from being painted.
</P>
<P>In the case of the options window in the kiosk application, WM_ERASEBKGND is used to draw the window border. The relevant portion of the <I>OptionsWndProc</I> window procedure is shown below:</P>
<!-- CODE //-->
<PRE>
  LRESULT CALLBACK OptionsWndProc(
    HWND hwnd,
    UINT message,
    WPARAM wParam,
    LPARAM lParam)
  &#123;
    HDC hdc;
    UINT nID;
    RECT rc;
    switch(message)
    &#123;
    //Other message handlers */
    //&#133;
    case WM_ERASEBKGND:
     HBRUSH hBrushOld;
     hdc = (HDC)wParam;
     GetClientRect(hwnd, &#38;rc);
     hBrushOld = (HBRUSH)SelectObject(hdc,
      GetStockObject(WHITE_BRUSH));
     Rectangle(hdc, rc.left, rc.top,
      rc.right, rc.bottom);
     InflateRect(&#38;rc, -3, -3);
     Rectangle(hdc, rc.left, rc.top,
      rc.right, rc.bottom);
     SelectObject(hdc, hBrushOld);
     return (TRUE);
    default:
     return (DefWindowProc(hwnd, message, wParam, lParam));
    &#125;   //End of switch(message) statement
  &#125;
</PRE>
<!-- END CODE //-->
<P>The WM_ERASEBKGND handler first extracts the HDC of the options window from the <I>wParam</I> parameter of the window procedure. Next it gets the coordinates of the options window client rectangle by calling <I>GetClientRect</I>. It then selects the stock object WHITE_BRUSH into this device context. Any subsequent graphics function calls that fill a rectangle or region will thus use white as the fill color.</P>
<P>The two <I>Rectangle</I> function calls result in the border being drawn. The first <I>Rectangle</I> call fills the entire client area of the options window with white. The effect of the second <I>Rectangle</I> call is to draw the black inset border. This happens for two reasons. First, the <I>InflateRect</I> call decreases the dimensions of the rectangle to be drawn. Second, the outline of a rectangle drawn by <I>Rectangle</I> is the color of the pen currently selected into the device context specified by the <I>hdc</I> parameter. Since this pen is black by default, the rectangle border is black.</P>
<P>Note that we have to make the first <I>Rectangle</I> call to fill the entire client area before drawing the inset border. Since the message handler code returns TRUE when it&#146;s done, the default WM_ERASEBKGND processing is skipped. If the first <I>Rectangle</I> call is not made, only the inset rectangle would ever get drawn by our WM_ERASEBKGND message handler.</P>
<P><FONT SIZE="+1"><B><I>Creating and Drawing the Options Buttons</I></B></FONT></P>
<P>We&#146;ve seen how the options window is created. But what about the three owner draw buttons that the window contains?
</P>
<P>The three owner draw buttons in the options window are created in response to the WM_CREATE message sent to <I>OptionsWndProc</I>:</P>
<!-- CODE //-->
<PRE>
  /* Global variables and child control
    identifiers defined in kiosk.h */
  #define IDC_BALANCE   1028
  #define IDC_DEPOSIT   1029
  #define IDC_WITHDRAW  1030
  HDC hdcButtons;
  HBITMAP hBmpButtons;
  HWND hwndBalance;
  HWND hwndDeposit;
  HWND hwndWithdraw;
  LRESULT CALLBACK OptionsWndProc(
    HWND hwnd,
    UINT message,
    WPARAM wParam,
    LPARAM lParam)
  &#123;
    HDC hdc;
    UINT nID;
    RECT rc;
    switch(message)
    &#123;
    case WM_CREATE:
     hdc = GetDC(hwnd);
     hdcButtons = CreateCompatibleDC(hdc);
     hBmpButtons = LoadBitmap(ghInst,
      MAKEINTRESOURCE(IDB_BALANCE));
     SelectObject(hdcButtons, hBmpButtons);
     ReleaseDC(hwnd, hdc);
     hwndBalance = CreateWindow(TEXT("BUTTON"), NULL,
      WS_VISIBLE|WS_CHILD|BS_OWNERDRAW,
      &#133;,
      (HMENU)IDC_BALANCE,&#133;);
     hwndDeposit = CreateWindow(TEXT("BUTTON"), NULL,
      WS_VISIBLE|WS_CHILD|BS_OWNERDRAW,
      &#133;,
      (HMENU)IDC_DEPOSIT,&#133;);
     hwndWithdraw = CreateWindow(TEXT("BUTTON"), NULL,
      WS_VISIBLE|WS_CHILD|BS_OWNERDRAW,
      &#133;,
      (HMENU)IDC_WITHDRAW,&#133;);
     return (0);
     //Other message handlers
     //&#133;
     default:
      return (DefWindowProc(hwnd, message, wParam, lParam));
     &#125;    //End of switch(message) statement
  &#125;
</PRE>
<!-- END CODE //-->
<P>The WM_CREATE handler does more than just create the three owner draw buttons. It also loads the bitmap containing the button images and selects that bitmap into a global memory device context called <I>hdcButtons</I>.</P>
<P>The button images are stored in one bitmap as shown in Figure 9.5. Each button has a pair of 48-pixel-wide images. The first image in the pair is used to draw the button&#146;s unpressed state. The second is used to draw its pressed state.</P>
<P><A NAME="Fig5"></A><A HREF="javascript:displayWindow('images/09-05.jpg',290,55 )"><IMG SRC="images/09-05t.jpg"></A>
<BR><A HREF="javascript:displayWindow('images/09-05.jpg',290,55)"><FONT COLOR="#000077"><B>Figure 9.5</B></FONT></A>&nbsp;&nbsp; Options window button image bitmap.<P><BR></P>
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