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elaboration of before-and-after tag; spec change

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- RTL tag removed
- we're calling the program part "the font compiler"
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minjaesong
2018-08-24 00:37:48 +09:00
parent 2e10249f27
commit 2702f850c2
1 changed files with 11 additions and 6 deletions
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17
CONTRIBUTING.md
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@@ -36,12 +36,12 @@ Although the font is basically a Spritesheet, some of the sheet expects variable
Width is encoded in binary bits, on pixels. On the font spritesheet, every glyph has vertical dots on their top-right side (to be exact, every (16k - 1)th pixel on x axis). Above image is a sample of the font, with width information coloured in magenta. From top to bottom, each dot represents 1, 2, 4 and 8. For example, in the above image, ! (exclamation mark) has width of 5, " (double quote) has width of 6, # (octothorp) has width of 8, $ (dollar sign) has width of 9.
### Glyph Tagging System
### Glyph Tags
Green-tinted area (should be 10 px tall) contains the tags. Tags are defined as following:
```
(LSB) 0 == RTL
(LSB) 0 == Use Compiler Directive (Undefined right now, keep it as 0)
1 -+ 1 | Align to this X pos of prev char,
1 | 2 | only valid if write-on-top is 1
1 | 4 | and is centre-aligned and non-zero
@@ -70,15 +70,20 @@ Since this tag does not make sense for diacritics, they will use the value for c
#### Diacritics That Comes Before and After
When this tag is set, the font compiler will replace this glyph with two extra code points given in the bitmap.
To implement those, this two extra code points are needed, which are provided in the Unicode's Reference Chart (www.unicode.org/charts/PDF/Uxxxx.pdf) The code points must be "drawn" in the bitmap, in the same manor as a tagging system. The zeroth column (x = 0) has the "before" character, the first column (x = 1) has the "after". All nineteen pixels (bits) are read by the font, which encompasses U+0000..U+EFFFF
For working examples, take a note at the bengali sprite sheet.
This tag can be used as a general "replace this with these" directive, as long as you're replacing it into two letters. (e.g. U+0B94; TAMIL LETTER AU, which is a combination of U+0B92 and U+0BD7
NOTES:
- If the diacritics comes before AND after the glyph (e.g. U+103C), "Align before the glyph" must be set too.
- If glyphs are right or centre aligned, they must be aligned in the same way inside of the bitmap; the program assumes every variable-width glyphs to have a width of 15, regardless of the tagged width.
- If the diacritic is aligned before the glyph, the diacritic itself is always assumed as left-aligned, as this font will exchange position of said diacritic and the glyph right before it.
Also note that the font compiler will not "stack" these diacritics.
#### NOTES
- If glyphs are right or centre aligned, they must be aligned in the same way inside of the bitmap; the font compiler assumes every variable-width glyphs to have a width of 15, regardless of the tagged width.
- If the diacritic is aligned before the glyph, the diacritic itself is always assumed as left-aligned, as the font compiler will exchange position of said diacritic and the glyph right before it.
![Visual representation of left/right/centre align](alignment_illustration.jpg)