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INFO: Calculating Text Extents of Bold and Italic Text

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Summary

GetTextExtent() can be used to calculate the extent of a string. The value returned may need to be adjusted, depending upon the style of the font. When an italic or bold font is requested and none are available, the Graphics Device Interface (GDI) may simulate those styles using an existing raster or vector font.

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More information

GDI-simulated bold and italic fonts both include overhangs. The overhang is specified in a TEXTMETRIC structure obtained by calling the GetTextMetrics function. The proper method for calculating the extent of a line of italic or bold text is shown below: 
   dwExtent = GetTextExtent(hDC, lpString, nCount);
   GetTextMetrics(hDC, &tm);
   xExtent = LOWORD(dwExtent) - tm.tmOverhang;
Listed below are examples of italic text alignment. If the next character is not italic, the overhang should not be subtracted from the advance width returned from the GetTextExtent function. The overhang needs to be subtracted only when the next for text alignment character has the same style. 
                                        GetTextExtent yields
                                        this as the extent:

                                              ||
       /   /                                  \/ 
      /   /           /   / /   /         /   /|   |
     /---/           /   / /   /         /   / |   |
    /   /           /---/ /---/         /---/  |---|
   /   /           /   / /   /         /   /   |   |
       -----      /   / /   /         /   /    |   |
         ^            /\                      /\ 
      Overhang        ||                      ||
               Because the next        Start the nonitalic H
               character is italic,    here because it does not
               start the next          slant and would partially
               character within the    overwrite the previous
               overhang of the         italic character.
               current character
The overhang for bold characters synthesized by GDI is generally 1 because GDI synthesizes bold fonts by outputting the text twice, offsetting the second output by one pixel, effectively increasing the width of each character by one pixel. Calculating the advance width of the bold text is similar to the method for italic text. The GetTextExtent function always returns the extent of the text plus 1 for bold text. Thus by subtracting the tmOverhang(1), the proper advance is achieved. 
        ||   ||
        ||   ||
        ||===||
        ||   ||
        ||   ||
              ---<= This line represents the "extra" overhang of 1.
                /\ 
                ||
             GetTextExtent yields
             this as the extent of the
             bold H.
NOTE: This article applies only to Raster and Vectory Fonts. The GetTextExtent() family of functions always return advance widths of strings for TrueType fonts as described by ABC widths structure. For more information on ABC advance widths, see the GetCharABCWidths() function documentation.

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Article Info
Article ID : 74298
Revision : 5
Created on : 1/1/0001
Published on : 1/1/0001
Exists online : False
Views : 536