BUG: Setting Orientation Changes Background Mix Mode for Printer

MORE INFORMATION

The background mix mode of a device context (DC) affects text, hatched brushes, and pen styles that are not solid lines. The effect can be that the background changes so that text is not visible. The API function GetBkMode returns the current setting for the background mix mode for a specified DC and SetBkMode sets it. The mode can be Opaque or Transparent and has the following effects:

   Value         Description
   -----------   -----------------------------
   OPAQUE        Background is filled with the current background color
                 before the text, hatched brush, or pen is drawn.

   TRANSPARENT   Background remains untouched.
				

The background mix mode should be determined by the FontTransparent Property of the Printer object, which defaults to True, meaning that the mode should be Transparent. When you set Printer.Orientation, or use the Line method, it can have the undesired effect of also setting the background mix mode to Opaque, while leaving FontTransparent still set to True. The solution to this is to use the SetBkMode API function to set it back to Transparent. The following sample demonstrates the problem and a solution.

NOTE: This problem is printer driver-specific, meaning that the exact symptoms can vary from driver to driver. Some drivers do not experience this problem at all, while others reset the background mix mode to Opaque when any Printer object property is changed. This article describes the most common scenario. To make sure that you cover the worst possible case, you should call the SetBkMode function just before your Printer.Print calls. Then if you change any property of the Printer object, call SetBkMode again.

Steps to Reproduce Behavior

1. Create a new Project in Visual Basic. Form1 is created by default.
2. Add a CommandButton to Form1.
3. Paste the following code into the Form's module:

      Private Declare Function SetBkMode Lib "gdi32" _
      (ByVal hDC As Long, ByVal nBkMode As Long) As Long
   
      Private Declare Function GetBkMode Lib "gdi32" _
      (ByVal hDC As Long) As Long
   
      'For VB4 16-bit, replace the 2 lines above with the following 2 lines
      'Private Declare Function SetBkMode Lib "GDI" _
      (ByVal hDC As Integer, ByVal nBkMode As Integer) As Integer
   
      'Private Declare Function GetBkMode Lib "GDI" _
      (ByVal hDC As Integer) As Integer
   
      Private Const TRANSPARENT = 1
      Private Const OPAQUE = 2
   
      Private iBKMode As Long
   
      Private Sub Command1_Click()
            iBKMode = GetBkMode(Printer.hDC)
            Debug.Print "GetBkMode = " & iBKMode
            ' The next line may set the background mix mode to Opaque
            'Printer.Orientation = 1 ' May print correctly without this line
            iBKMode = GetBkMode(Printer.hDC)
            Debug.Print "GetBkMode = " & iBKMode
            Debug.Print "Printer.FontTransparent = " & Printer.FontTransparent
            Printer.ForeColor = &H80000008     ' black
            ' The Line method can also cause this problem:
            Printer.Line (100, 100)-(2800, 500), , BF
            iBKMode = GetBkMode(Printer.hDC)
            Debug.Print "GetBkMode = " & iBKMode
            Printer.ForeColor = RGB(255, 255, 255)   ' white
            Printer.CurrentX = 200
            Printer.CurrentY = 200
            ' The next line will reset the background mix mode
            'iBKMode = SetBkMode(Printer.hDC, TRANSPARENT)
            Printer.Print "Testing....."
            Printer.EndDoc
      End Sub
   					

4. Run the Project and click on Command1. Either a Page prints correctly with a black rectangle containing white text in the upper-left, and the Immediate Window displays the following: GetBkMode = 1
   GetBkMode = 1
   Printer.FontTransparent = True
   GetBkMode = 1
   
   or a page prints with a black rectangle in the upper-left containing a white rectangle instead of text and the Immediate Window displays the following:
   
   GetBkMode = 1
   GetBkMode = 1
   Printer.FontTransparent = True
   GetBkMode = 2
   
   In the latter case, it is the Line method that caused the problem.
   
   
5. Choose Stop from the Run menu or click on the Stop button to end the program.
6. Uncomment the line that sets Orientation, run the Project and click on Command1. If a page prints with a black rectangle in the upper-left containing a white rectangle instead of text, it indicates that setting the Orientation property changed the background mix mode and the Immediate Window displays the following: GetBkMode = 1
   GetBkMode = 2
   Printer.FontTransparent = True
   GetBkMode = 2
   
   
7. Uncomment the SetBkMode line, run the Project and click on Command1. ThePage prints correctly again with a black rectangle containing white text in the upper-left.