ID Number: Q74299
3.00 3.10
WINDOWS
Summary:
To create a font in the Microsoft Windows graphical environment given
only the required point size, an application must calculate the
logical height of the font because the CreateFont and
CreateFontIndirect functions use logical units to specify height. To
describe a font to the user, an application can calculate a font's
point size, given its height. This article provides the formulas
required to perform these calculations.
More Information:
To calculate the logical height, use the following formula:
Point Size * LOGPIXELSY
height = Internal Leading + -------------------------
72
LOGPIXELSY is the number of pixels contained in a logical inch on the
device. This value is obtained by calling the GetDeviceCaps function
with the LOGPIXELSY index. The value 72 is significant because one
inch contains 72 points.
The problem with this calculation is that there is no method to
determine the internal leading for the font because it has not yet
been created. To work around this difficulty, use the following
variation of the formula:
-(Point Size * LOGPIXELSY)
height = --------------------------
72
When an application calls the CreateFont or CreateFontIndirect
functions and specifies a negative value for the height parameter, the
font mapper provides the closest match for the character height rather
than the cell height. The difference between the cell height and the
character height is the internal leading, as demonstrated by the
following diagram:
---------- <------------------------------
| | |- Internal Leading |
| | | | <--------- |
| | | | | |- Cell Height
| |---| | |- Character Height |
| | | | | |
| | | | | |
---------- <------------------------------
The following formula computes the point size of a font:
(Height - Internal Leading) * 72
Point Size = --------------------------------
LOGPIXELSY
The Height and Internal Leading values are obtained from the
TEXTMETRIC data structure. The LOGPIXELSY value is obtained from the
GetDeviceCaps function as outlined above.
Round the calculated point size to the nearest integer. The Windows
MulDiv function rounds its result and is an excellent choice to
perform the above calculation.
Additional reference words: 3.00 3.10