KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q106018: BUG: SetPixel() Doesn’t Work Properly on a PS Printer

Article: Q106018
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kbOSWin310 _IK kbSDKWin16
Last Modified: 09-JUL-1999

3.10
WINDOWS
kbprg kbbuglist

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
-------------------------------------------------------------------------------

SYMPTOMS
========

In a Windows 3.1 printing application, calling the SetPixel() command on a
device context created for the Windows PostScript printer driver version 3.56 or
earlier causes the pixel that is drawn to be larger than expected if a line with
a thickness greater than 1 was drawn previously.

CAUSE
=====

The PostScript driver's implementation of SetPixel() draws a circle with the
thickness set to the thickness of the last line drawn with the LineTo() command
if the thickness of the pen used is greater than 1.

RESOLUTION
==========

Instead of using the SetPixel() command, use the PatBlt() command to draw the
pixel. This is needed only if a pen of width greater than 1 was used to draw
lines with the Moveto() and LineTo() commands.

For example, if you were calling SetPixel() using the following line of code to
draw a black pixel at coordinates (10,10)

     SetPixel(hPrnDC, 10, 10, RGB(0,0,0));

instead of the above line of code, you could use PatBlt() in the following
example:

     PatBlt(hPrnDC, 10, 10, 1, 1, BLACKNESS);

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

MORE INFORMATION
================

Once a pen of thickness greater than 1 (one) is created and selected into the
printer's device context and a LineTo() command is called, every call to
SetPixel() results in a circle the width of the pen. If a pen of width 0 (zero)
or 1 is created and used by the LineTo() command, the lines drawn will be the
correct thickness, but the SetPixel() command will still draw with the thickness
of the most recently used pen with a width greater than 1 (one).

For example, the following code will draw the first two pixels correctly. After
the pen of width 50 is created and selected into the printer's device context,
the first call to SetPixel works correctly because LineTo() has not been called
yet. The call to SetPixel after the line is drawn results in a circle the
thickness of the line. After that, a pen of thickness 1 is created and selected
into the device context. The line drawn afterwards is drawn correctly, but both
calls to SetPixel() result in thick circles.

Sample Code
-----------

     if (StartDoc(hPrnDC,&di) > 0)
     {
        HPEN hPen, hPen2, hOldPen;

        StartPage(hPrnDC);
        hPen = CreatePen(PS_SOLID,1,RGB(0,0,0));
        hOldPen = SelectObject(hPrnDC,hPen);
        SetPixel(hPrnDC,100,10,RGB(0,0,0));
        MoveTo(hPrnDC,220,10);
        LineTo(hPrnDC,700,10);
        SetPixel(hPrnDC,800,10,RGB(0,0,0));

        hPen2 = CreatePen(PS_SOLID,50,RGB(0,0,0));
        SelectObject(hPrnDC,hPen2);
        SetPixel(hPrnDC,100,110,RGB(0,0,0));
        MoveTo(hPrnDC,220,110);
        LineTo(hPrnDC,700,110);
        SetPixel(hPrnDC,800,110,RGB(0,0,0));

        SelectObject(hPrnDC,hPen);
        SetPixel(hPrnDC,100,210,RGB(0,0,0));
        MoveTo(hPrnDC,220,210);
        LineTo(hPrnDC,700,210);
        SetPixel(hPrnDC,800,210,RGB(0,0,0));

        DeleteObject(hPen2);
        DeleteObject(SelectObject(hPrnDC,hOldPen));
        EndPage(hPrnDC);
        EndDoc(hPrnDC);
     }

Additional query words: buglist3.10 3.10

======================================================================
Keywords          : kbOSWin310 _IK kbSDKWin16 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbbug
Solution Type     : kbpending

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.