About the placement of glyphs within their boundin box, are there general rules to follow?
I have found that, in general, both the lsb and the rsb of the capital letter A are zero. For the capital letters V and W there are slight variations: just positive, equal to zero, in some cases equal to zero the lsb and slightly negative the rsb.
Now, are there general principles or does nothing prevent me, for example, from setting a positive bearing for A?
A serif typeface can often have different metrics for the right side bearing (RSB) and left side bearing (LSB) on 'symmetrical' glyphs such as /H/ and /O/. Glyphs calculates RSB/LSB values from the closes point to a side bearing, so with serif typeface it's the serifs themselves.
Glyphs has a clever feature that's not widely known (or used) by many people. You can define a sidebearing measurement from the stem rather than the serif, which allows you to alter the length of serifs without the need to adjust metrics. For example, typing "[email protected]" for the LSB of the /E/ will result in the /E/ taking the metic value from the /H/ on the x axis at 300 units. This can be a timesaver as multiple glyphs can be assigned to the /H's metrics value at the stem rather than the serif. It's a quick way of spacing if you're defining stem to stem values for serif typefaces. The same works for the /oslash/ if the extreme points of the slash are wider than the /o/. It sounds confusing but it's easy to get understand when attempted.
Glyph Spacing and Optical Metrics
Regardless of the font editor, serif fonts' spacing should always be measured from the stems, ignoring the serifs. This may be what you are seeing when you say most serif characters like /H are not centered. They very likely are -- when measured to the stems.
I downloaded FontCreator and now I try this function on my Windows partition (usually I work on Linux).
In addition: the side bearing for the lower case must first be fixed. In a second moment the one for uppercase. However, since the words in capital letters are very few and in general a capital letter is followed by lower case, it is more important to arrange (before going to kerning) the all uppercase or the uppercase / lowercase sequence? Or is the latter phase mainly played with kerning?
Precisely because in serif shapes are asymmetrical, which point should I consider as a starting point for measurement? For example, in the glyph of this / M where do I identify the starting point for lsb and rsb?
It seems quite symmetrical, but the glyphs seem a little too "close" and such as to give a larger bearing, at least for capital letters
I find it important to establish a standard height for sidebearing measurement, that is then used not only across all the glyphs in a font, but also across all the fonts in a family. This is the only way to obtain consistent relative spacing between regular and bold, roman and italics, etc.
For a typical Latin typeface with caps and lowercase, my standard spacing height is usually somewhere around the midline of the x-height letters. That is then useful for all the lowercase letters with stems and bowls, and often for diagonals, and for uppercase letters with stems and usually diagonals. Uppercase letters with bowls are usually exceptions that I space with sidebearings off the extrema, and letters with apertures like C E F L, etc. need to be spaced by eye.
FontLab has a 'measurement line' that can be set and fixed at a standard height across a font, which is very useful for my method.
Thank you for your always precious informations.
As written before, do you have any updated text / guide to report on the font design?
I typically start out by putting the spacing measurement line a little more than halfway to the stem of the lowercase i. Then I check where it is sitting on the lowercase o. Presuming the o has curved sides, I try to find a height at which the left and right sidebearings at the measurement height would be equal on both sides.
As far as I understand, the measurement line is only handy insofar as it gives a quick way of insuring that other letters with identical (or sufficiently similar) side shapes get related sidebearings. If the sides of /x/ are unique, then taking that measurement doesn't matter, as that info won't be carried to other glyphs. Just make nnxnnooxoo look good. If, say, your /k/ is quite similar on the right side, then linking the sidebearings of the two glyphs might be called for. In that case the sidebearings can be measured at any altitude where the shapes are identical (or sufficiently similar). (These measurement-line sidebearings are all just tools within the font editing app, of course, which will in the end write the technical sidebearing and advance width to the font file.)
But maybe I'm missing something. I confess I don't follow @John Hudson's note about using a measurement line to insure consistency across fonts in a family. Is the idea there that sidebearings of flat-sided and round letters are similar in proportion to each other? (It seems obvious to me that the differing shapes of sloped or emboldened glyphs wouldn't call for direct reuse of sidebearings.)
Modern font tools tend to have an option to view slanted sidebearings in italics, but I still want to know the height at which measurements between stems and actual sidebearings are calculated.
It is also worth considering the purpose of the typeface. For example, the text fonts are needed more white space between black shapes so its sidebarrings are looser comparing to display fonts.