Re: [Devel] 'tension' in splines, Hermite Splines [Re: Rendering (by FreeType) and hinting of Latin small 'a']

[oergiR]

Hello Vadim,

Just a reaction to the TrueType bits...

> Well, I have checked today, with help of TtfMod, complexity of so-called
> "well-hinted TrueType fonts". In particular, Times New Roman TTF.
> And I can tell you that level of complexity I found, far exceeded my
> expectations!
> Here are some numbers illustrating TNR complexity.
> Number is number of instructions, to be precise: instructions+operands,
> executed by interpreter.
> And this doesn't include calls to subroutines!
>
>   capital small
> A 427 596
> (...)

> Returning to samll Latin 'a' - it required 596 bytes (opcode+operands) for
> *right* hinting and good rendering.

This is opcodes+operands as you say. The actual number of instructions
executed for "a" is 236 (including function calls), and something around 425
for nonsquare pixels. I believe these figures are mostly due to the large
amounts of delta hints, which are almost never needed when using an
anti-aliased rasteriser, in my experience.

Georgia, which is hinted far better than TNR, if you ask me, executes only
99 to 103 instructions for "a".

> Depending on outline quality and origin (TTF or PS Type1), FontLab's
> auto-hinter produced from 7 to 15 *high-level* TrueType hints.
> I name them high-level, as NimbusRoman and NimbusSans TTF's have 196 and
170
> operations(addresses) for 'a'. At least that's what TtfMod tells me.
> So it seems FontLab translates those *high-level* TrueType hints into
> low-level TT opcodes, complements them with stack data, etc.
>
> My point is that 15 operations per glyph are *reasonable*, and can be
> overviewed/hinted by a man (as you can see from URL above, TT auto-hinter
> results in FL4 are acceptable in mnay cases, but need correction by hand)
> 196 operations, not speaking about 600, can't be coded by a man.

As you say, the number of "operations" is the important thing. I am right
now working on a compiler which takes something looking like C and produces
TT instructions. Without delta hints, I use about 20 to 40 lines per glyph,
which compile to about 10 times those amount of bytes in the instructions.
IMO, a few thousand lines per font can be coded.

> (....)
> Problem is that TrueType outlines have *too many* points, and this
*decreases*
> font quality in most cases.

This is true, also because of the conversion from Bezier splines. I'm not
sure, however, this actually causes a lower font quality.

> (....)

Bye,

Rogier