A font contains glyph designs.
An application scales the designs to whatever size is needed.
The display consists of a whole number of pixels. Consequently there may be rounding effects.
I wonder if you might like to try the following experiment.
Obtain a copy of my Style Art font. It is a free download from the following web page.
http://www.users.globalnet.co.uk/~ngo/fonts.htm
The direct link is as follows.
http://www.users.globalnet.co.uk/~ngo/STYLEART.TTF
Install the font.
Using the software application in which you are trying your own font, using the Style Art font, try typing the figure 1 a number of times, then press the RETURN key and then type the figure 1 a number of times again. The figure 1 glyph is a solid 2048 font unit by 2048 font unit square shape in the Style Art font.
Does the top of the second line of the display touch the bottom of the first line of the display?
If the answer is yes, then it could be your font which needs adjusting.
If the answer is no, then it could be a line spacing setting with the application which needs adjusting.
I do not know if the use of the 1200 figure is the problem, yet I usually use the following way of proceeding.
I set the positive metric values as 2048, the negative metric values as minus some multiple of 256 and the gap values as 0. This is because Windows uses "four times the point size divided by 3" as the number of pixels to render the 2048 font units of the "above the x-axis" part of my fonts and additional pixels at the same rate to render the "below the x-axis" part of my fonts.
For example, if I produce a font which goes from -768 to 2048 vertically, then the number of pixels vertically at 24 point can be calculated as follows.
The number from the "above the x-axis" part is 4 times 24 divided by 3 pixels, which is 32 pixels. 32 times 768 divided by 2048 is 12, so 32 plus 12 is 44 pixels for the rendering.
Please note how the calculations came out as whole numbers. If they did not come out as whole numbers then there could be rounding effects.
Changing your 1200 metric to 2048 could perhaps cause your font to make the rendering task of the software application easier, by avoiding it having to make rounding decisions. However, this is just a thought, it may perhaps not improve the situation at all. However, it might be worth trying unless it would mean a huge amount of work redesigning your font.
William Overington
26 February 2007