Printing using GDI+ : a few tips

• gdipprinter.zip - 18 Kb

Introduction

This articles gives some hints on printing figure made with GDI+. As anybody knows, printing is one of the most mysterious feature in MFC (this is my point of view). It is not well (at all) documented and in fact, the best examples can be found in CodeProject Printing section.

Since GDI+ is a new technology, it brings new problems when trying to print.

In the following, I will try to give some hints encountered when trying to print GDI+ stuff. I will suppose that you have some basic knowledge about printing, especially that you have read one of the following articles, so I won't have to discuss about getting a printer DC working and other details already in those article but rather focus on GDI+ problem related:

• Printing support functions, Michael A. Barnhart
• Printing tips and tricks from the trenches, Roger Allen

In the following, dc denotes the printer dc and graphics denotes the GDI+ graphic context:

    CDC dc;
    Graphics graphics;

Setting the mapping modes

The mapping modes of dc and graphics must be tuned together:

    dc.SetMapMode(MM_TEXT);
    graphics.SetPageUnit(UnitDocument); 

With those setting, each logical unit is converted to 1 device unit (MM_TEXT) and one device unit is 1/300 inch (UnitDocument). So we get 300dpi printing, great.

What about other DPIs?

Gulp, we got it working for 300dpi, but what about 600 dpi? or 1200 ?

After a few try and error, I figured out we had to do the dirty job ourselves, that is check for the dpi of printer and scale accordingly the graphic:

1. Get the dpi ratio dpiRatio:

       CPrintDialog MyPrintDialog;
        ...
        // the dpi of printer is enclosed in DEVMODE structure,
   
        DEVMODE* pDev=MyPrintDialog.GetDevMode();
       // getting dpi ratio between 300dpi and current printer dpi
   
       double dpiRatio=300.0/pDev->dmPrintQuality;
       // deallocating memory for pDev
   
       VERIFY(GlobalUnlock(pDev));
   

2. Setting page scale in to graphics

       graphics.SetPageScale(dpiRatio);
   

That ugly hack should do the work. Of course, any nicer method is welcome :-)

What about text?

Getting font size

Unfortunately, scaling the graphic is not sufficient and Dpi scaling has to be taken in account when computing the font size!

Here's a modification of the CreateFontSize of Barnhart article. As you see, the user has to pass the dpiRatio to scale the font accordingly:

int CreateFontSize(HDC hDC, int points, double dpiRatio)
{
	// This will calculate the font size for the printer that is specified

	// by a point size.

	//

	// if points is:

	//  (-) negative uses height as value for Net Font Height (ie. point size)

	//	(+) positive height is Total Height plus Leading Height!

	ASSERT(hDC);
	
	POINT size;
	int logPixelsY=::GetDeviceCaps(hDC, LOGPIXELSY);
	size.x = size.y = MulDiv(points, logPixelsY, 72);

	// here we scale the font...

	return (float)floor(size.y*dpiRatio);
}

Create font for printing

When creating a font, use the following unit:

Unit fontUnit = m_pGraphics->GetPageUnit();
// if fontUnit is UnitDisplay, then specify UnitPixel, 

// otherwise you'll get a "InvalidParameter" from GDI+

if (fontUnit == UnitDisplay)
fontUnit = UnitPixel;
// classical constructor use, lfHeight is the font height

Font font(&fontFamily, CreateFontSize(hDC, 
          lfHeight, dpiRatio), FontStyleRegular, fontUnit);

Credits

A lot of useful article available on the Printing section:

• Printing support functions, Michael A. Barnhart
• Printing tips and tricks from the trenches, Roger Allen
• Printing without the Document/View framework, Chris Maunder

Update History

11/09/2002

Fixed problem of text changing size when playing with the zoom in preview mode. Updated the demo project.