Hi Stef,

----- Original Message ----- 
From: "stephane ducasse" <stephane.ducasse at free.fr>
To: "The general-purpose Squeak developers list"
<squeak-dev at lists.squeakfoundation.org>
Sent: Sunday, April 29, 2007 10:52 AM
Subject: Font rendering strategy


> Hi guys
>
> I want to thanks andy and juan for their work!
> Now I need your brain and knowledge.
> I'm totally ignorant of font problems/challenges but
>
> How can we get the best of both works?

The two approaches are different, and each solves a different set of problems.
What ~I~ want from a font system is...
    1. Automatic access to all the fonts in my host OS.
    2. The ability to use them at any point size.
    3. The ability to render in any colour, on any background (including a
transparent background)
    4. Optional support for sub-pixel anti-aliasing, without compromising points
1, 2 and 3.
    5. Unicode support (in my case, not so much for language support, but rather
for access to mathematical symbols)
    6. Better support for printing (e.g. scale up a TextMorph's contents to my
printers dpi, and output as a .png)
    7. Support for different underline/strikethrough styles (e.g. text in black,
underline in red; jagged underline; double strikethrough)
    8. Support for subscript/superscript; raised/lowered text.

FreeType solves points 1 and 2, but they could also be solved by grabbing font
info, glyphs, and metrics directly from the OS.
Something similar to the Win32 Native Fonts package. (This is something I would
like to do in the future - with the ability to grab ClearType/sub-pixelled
glyphs on Windows, and something similar on Macs).

The BitBlt plugin enables 3 & 4.

Points 6, 7 & 8,  I haven't done much with.
But, for example, I render underline and strikethrough as a separate BitBlt
operation, rather than modifying the glyphs to include
underlining/strikethrough. So it should be easier to include different styles.


> What are the exact pros and cons in terms of:
> - font

My approach gives you access to fonts, without requiring that you import them.
Juan's approach allows you to selectively import fonts, and to subsequently edit
them.

My approach allows easy use of any point size.

Juan's approach caches the glyphs/metrics in the image, so if the image is
distributed, then the font (file) does not need to exist on the target machine.
My approach deliberately clears any cached glyphs/metrics on image save so
that...
    a. there is no danger of violating font licenses by shipping cached data
    b. if the same font exists on the target machine, but is a different
version, then the target machine's version wins (Arial on Windows 98 is not
necessarily the same as Arial on Vista, or on Mac OS X)

I also support kerning and sub-pixel positioning for nice 'WYSIWYG' text layout.

> - size

:) Size of what?
The image? My approach has more code, but I don't cache glyphs/metrics in the
saved image.
VM? My approach requires the FT2Plugin, & the FreeType library on Windows/Mac.

> - memory consumption

I have a glyph cache whose maximum memory consumption can be set by the user
through a Preference.
The default is 5 MBytes.
The FreeType library also has a fixed overhead, plus an overhead per font that
is used (not every font on the host OS, only those that are actually used within
the image).
I have tested my stuff on a 7 year old PIII with 64MBytes RAM, and it runs quite
happily.

With Juan's approach it will depend upon the number of fonts/point sizes that
are imported into the image.

>
> It seems that juan work is excellent for OS independence.

Yes.
Shipping glyphs in the image  is a good way to ensure that they are available on
all platforms.
But I am not sure of the legality of that. For monochrome bitmap glyphs I think
it is ok. But when the glyphs have been anti-aliased, or sub-pixel anti-aliased,
I don't know?

I take a different approach and revert to using a strike font if any one of the
FT2Plugin, the FreeType library, or a particular font file is absent from the
user's machine. So any image, or project, should still be runnable and useable
on any OS.

Cheers,
Andy