Merging two glyphs

[elipsett]

I need to create a font full of graphic symbols. I'm using a standard Latin font as the basis, but every keyboard letter corresponds to a symbol.

I need a way to combine, for example, the symbol for A with the symbol for B. For ease of discussion, assume that symbol A is a circle, and symbol B is a dot. When they are combined, the result is a circle with the dot in the middle. Symbol A and symbol B are created with the same bounding box and center point, so it is sufficient to actually overprint them, if that helps understand the amount of adjustment needed.

I assume this is handled with pair adjustment, but it is extremely unclear if that is the right approach, and how to implement it if it is the right approach.
I have been using FontCreator to create non-Unicode glyphs for CJK languages for many years, but these are usually single glyphs in an otherwise empty font. I am not familiar with using FontCreator functions like kerning, pair adjustment, scripts, etc., and I'll probably need to be led by the hand.

Any assistance will be appreciated.

[Bhikkhu Pesala]

Do you want the dot to overlay the circle when you type A followed by B?

In that case, design B like a diacritical mark with zero advance width and a negative left side-bearing.

If you want a third glyph — a circle with a dot — when you type C, then create C as a composite glyph, with components A and B.

[elipsett]

> Do you want the dot to overlay the circle when you type A followed by B?

That would be the easiest solution.

> In that case, design B like a diacritical mark with zero advance width and a negative left side-bearing.

Thank you. This seems reasonable.
I will attempt to figure out how to do that from the documentation.

[elipsett]

This does not appear to work.

I need base 1 (circle) to exist by itself, as 1A (circle with mark A), as 1B (circle with mark B), etc.　Likewise, I need a base glyph 2 (square) for 2 by itself, 2A, 2B, etc.

So the following pairs need to be defined:
1A, 1B, 2A, 2B, etc.

I have defined a MarkPositioning script under Scripts/Latin/Default
I have a list of Base items 1 and 2
I was able to specify 1A, but when I attempt to specify 2A it says “This mark glyph/group already exists.”
However, the displayed merged glyphs for both 1A and 2A correctly overlaid.
I then tried to create 1B and it gave me the same error message.
I created a second subtable, and was able to create 1B and 2B, both displaying normally.
Apply and OK.
When I try the font and press 1 and then A, it displays the two characters sequentially. Likewise the other combinations.

So either we misunderstood each other, or I’m doing something wrong.

[Bhikkhu Pesala]

If you want a third glyph — a circle with a dot — when you type C, then create C as a composite glyph, with components A and B.

Look at any standard font to see how diacritics work with base glyph A, and accented versions: Á À Ä Ã Å Â etc.

[elipsett]

If my understanding is correct, a composite glyph is a new glyph, in the font, created by combining two elements. That new glyph is assigned to a new codespace in the font.

I need a lot of glyphs, and if there is some way to make a bunch of bases, and separately a bunch other modifying glyphs, and be able to combine them through keyboard input, then I only have to create 1, 2, A, B, C = five glyphs, instead of 1A, 1B, 1C, 2A, 2B, 2C = six glyphs. And I have a lot more than just 1, 2, A, B, and C.
If I have, for example, 10 letters and 10 numbers, then with composite fonts I would need I believe, 120 glyphs (root forms + composites). If they can be mixed on the fly, then I only need 20.

Is there any way to do this?