Chapter Five Fonts

With the TrueType fonts, it doesn't much matter what mapping mode you use; simply choose a font height and go for it. No need to worry about points.

If you're using the CDC::GetTextExtent function to calculate line breaks, the screen breakpoint will occasionally be different from the printer breakpoint.


Index Description Value HORZSIZE Physical width in millimeters 320 VERTSIZE Physical height in millimeters 240 HORZRES Width in pixels 640 VERTRES Height in raster lines 480 LOGPIXELSX Horizontal dots per logical inch 96 LOGPIXELSY Vertical dots per logical inch 96 1 inch = 25.4 mm
Using the values above and the fact that there are 25.4 millimeters per inch

physical display size:
320mm/ (25.4mm/inch) = 12.60 inch
240mm/(25.4mm/inch) = 9.45 inch
The physical display size is 12.60-by-9.45 inches,

logical size:
640pix/(96pix/inch) = 6.67inch
480pix/(96pix/inch) = 5.00inch
The logical size is 6.67-by-5.00 inches.

So the physical size and the logical size need not be the same.


For Windows NT 4.0, it turns out that HORZSIZE and VERTSIZE are independent of the display resolution, and LOGPIXELSX and LOGPIXELSY are always 96. So the logical size changes for different display resolutions, but the physical size does not. For Windows 95, the logical size and the physical size are equal, so both change with the display resolution. (At a resolution of 640-by-480 pixels with Windows 95, HORZSIZE is 169 and VERTSIZE is 127.)

So, for Windows NT, text is smaller on a small monitor; but that's not what you want. Instead, you want your font sizes to correspond to the logical display size, not the physical size.

You can invent a special mapping mode, called logical twips, for which one logical unit is equal to 1/1440 logical inch. This mapping mode is independent of the operating system and display resolution and is used by programs such as Microsoft Word. Here is the code that sets the mapping mode to logical twips:


pDC->SetMapMode(MM_ANISOTROPIC);
pDC->SetWindowExt(1440, 1440);
pDC->SetViewportExt(pDC->GetDeviceCaps(LOGPIXELSX),
                    -pDC->GetDeviceCaps(LOGPIXELSY));