Auto Metrics with Fixed Width currently alters the LSB and RSB of each affected glyph equally. This is good for most situations, but maybe not all. I would propose a “Balance Slider” that give the % of alteration to be done on the LSB vs the RSB. Center position (the default) would be 50% - the current behavior. Full left would be 100% LSB and 0% RSB. Full right would be 0% LSB and 100% RSB.
My need is rather arcane, I admit. In a fixed width font, I would like to set the advance width by altering the RSB only (i.e. change only the Advance Width.) This is so that I can half the advance width of all double-wide CJK characters to match the single-wide characters (thereby satisfying the requirement that all glyphs have the same advance width) and then add an OpenType mapping to render a space after each CJK. (Although I have not yet tested this … one wrinkle is that the Windows GDI might automatically use (xAvgCharWidth x 2) for CJK glyphs …)
This also works with combining marks using GPOS . It appears that combining marks still need a non-zero advance width in fixed-pitch fonts. I believe that Monotype Consolas and Courier New use GPOS settings in this way, and that does seem to work.
