Microsoft KB Archive/106018

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BUG: SetPixel Doesn't Work Properly on a PS Printer

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Q106018

3.10 WINDOWS kbprg kbbuglist

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) 3.1

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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

Issue type : kbbug

Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310