What style face are you looking for? What's the feel you're going for?

Without any context, I would say an open, humanist sans … whether you use text or lining figures would depend on the context; for isolated digits, lining might be better.

firstly, thank you for the answer :)

What style face are you looking for? What's the feel you're going for?

this is something I may decide later; the readability issue is my primary concern now in the sense that any non-readable solution would be unacceptable.

Yes, they are isolated 0-9 digits; just to give you something to picture in your mind, consider a single digit "flying" around on an empty screen like if it were thrown on screen from a randomish angle from the outside, following a physical ( hence possibly rotating, 3d ) motion.

Now, the problem is that ambiguous digits like 6 vs 9 ( so some kind of visual aid is needed, like an "underscore" fixing the orientation ( sorry, I don't know the technical term :) ) ), those resembing each other like 1 and 7, or those resembing each other when "spinning" like 0 and 8, 3 and 5 etc ... can make digit recognition hard. Is there some "general purpose" typographic trickery to minimize these sort of effects ?

If the numbers are rotating, 6 and 9 would indeed be a problem unless you indicate which way is up. Whatever solution you come up with (an underscore, for example), I'd apply it to all numbers for consistency.

I would think that any font that is very legible should work, but you really need to run tests.

"this is something I may decide later"

The problem is that there are legible typefaces in many different styles (or at least serif and sans). Finding an easily legible font is not the problem. You need to decide what feel you want first in order to narrow down the selection.

Your approach, with all due respect, is a bit like painting a room and going to the paint store and asking which paints are the most durable (or whatever) before you've chosen a color. You want to be asking "which orange paint is the most durable" … or whatever. Make sense?

Your approach, with all due respect, is a bit like[...]Make sense?

I understand your point and I would agree with you in most cases, but IMHO this is a different story. The problem is not legibility in a general sense, it's the specific requirement of designing digits to be recognizable ( not comfortably readable and/or estethically pleasing ) while moving/rotating.

Imagine a NASA engineer asking you to design digits for zero-gravity labels ( say, in the international space station ) optimized to allow astronauts to "grasp" numbers even if upside down, or while rotating in mid air... would you really ask him first the "feel" of the typeface ?

following your example, if the painting durability were my primary requirement then its color would be an irrilevant decision. Just to give you a concrete example, do you know those paintings used to protect the hull of boats from marine vegetation ? ideally, one would like to match the color to the main hull color, but sometimes this is not possible because some active ingredients in the painting already act as a pigment ... so, asking "which orange paint is the most durable" would just make them laugh at you in this case :)

I would think that any font that is very legible should work, but you really need to run tests.

yes, I'll do; probably, I will end up designing them from the ground up; after all, it should be just 10 isolated symbols in 2-3 different sizes ( eventually, I'll come back here if I have problems ) ... just hoped someone already did it for me :), thanks

Six and nine will always look like each other when inverted, even with different glyph shapes.
Therefore, it is necessary to place an underline beneath all figures, or use a device which treats top and bottom of glyphs differently, such as “top-heavy” or color.

> Imagine a NASA engineer asking you to
> design digits for zero-gravity labels

Astronauts don't read numbers upside down. They are either seated or standing in a predetermined orientation.

You're making this problem harder than it really is. Any legible font should work well as long as you use underscores (or some other method).

Pick a legible font that fits the style of the game. If people have trouble reading it, adjust the timing to slow it down.

If people have trouble reading it, adjust the timing to slow it down.

I've already done that and the result is acceptable, but still unoptimal; essentially, the timing and the "trouble" in recognizing numbers are part of the game mechanics, and the problem is exactly to trick the player without annoying him too much ( and confusing 6/9, or 1/7 happens to be annoying ) while preserving a "sophisticated" graphical touch. It's a perfectionism thing ...

Pick a legible font that fits the style of the game.

sure, but the converse may work too, ie fit the game style to the type face instead, as long as it's worth it, of course.

Therefore, it is necessary to place an underline beneath all figures, or use a device which treats top and bottom of glyphs differently, such as “top-heavy” or color.

I've already experimented with the "top-heavy" idea but I always ends up with either an inelegant "fat effect" or a pompous feel ( like a perspective deformation of some heavy-tall-column ) or some other "exaggerated" effect.

the underscore is easy ( and it's my current solution, by the way ) but it gives an "engineer"-like feeling. This is not bad per se, indeed I can always give to the overall style a more "technical" touch instead.

as already said, I need some more experimentation ... thank you everybody !

Italized?

I have seen used periods to distinguish between 6. and 9.

Another approach might be to place the numbers inside a shape that's always oriented a certain way.