Proposal: Drop ttf-cjk-compact, get fonts-droid

[Kenshi Muto <kmuto@debian.org>]

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(This proposal relates with "Future of ttf-cjk-compact", <[🔎] 20150715074128.GN6751@mraw.org>)

Hi,

This is a proposal to replace ttf-cjk-compact with fonts-droid for next (Stretch)
debian-installer.

Introduction:
DroidSansFallback.ttf of fonts-droid package appears best choice for graphical
debian-installer to show CJK - Chinese, Japanese, Korean -, because it is
scalable font, quite small footprint (3939852 bytes), and enough legible.

ttf-cjk-compact was born in 2005, to display CJK characters on graphical
debian-installer. Due to lack of small scalable CJK font at 2005
and limited RAM disk size, I made a "workaround" font package ttf-compact-fonts
(former name). This font package made a list of "may use" characters from
d-i po files and some other packages, then rebuilt reduced font with the list
by modifying other font packages; vlgothic, unfont, and arphic-uming.
(ja.ttf: 197392 bytes, ko.ttf: 152000 bytes, zh.ttf: 1258276 bytes.
total: 1607668 bytes.)

After some tests, I believe it's time to use fonts-droid instead of
ttf-cjk-compact.

Test:
- - screenshots:  http://kmuto.jp/debian/d-i-font/sc/
- - graphical netboot mini.iso: http://kmuto.jp/debian/d-i-font/mini.iso (50MB)

Step:
1. Modify fonts-android to provide fonts-android-udeb which has only
   DroidSansFallback.ttf.
   patch:  http://kmuto.jp/debian/d-i-font/fonts-android.diff
2. After fonts-android-udeb is installed to the mirror,
   Modify d-i/installer to use fonts-droid-udeb instead of ttf-cjk-compact-udeb.
   patch:  http://kmuto.jp/debian/d-i-font/installer.diff
3. Remove ttf-cjk-compact from unstable and testing.

Pros:
 - d-i code gets smarter way.
 - most CJK characters will be shown correctly.
 - replacing ttf-cjk-compact with DroidSansFallback doesn't break
   other languages. (as far as I saw)
 - Chinese gets sans-serif.

Cons:
 - increases +2MB for each graphical initrd.
   jessie-amd64/cdrom/gtk/initrd.gz: 25557641 -> 281535694
                hd-media/gtk/initrd.gz: 27747025 -> 30340894
                netboot/gtk/initrd.gz: 34425758 -> 37539446
                netboot/gtk/mini.iso: 49283072 -> 52428800
 - Some Japanese characters look bit funny.
   (I believe it is negligible for installer.)

Note:
 - Noto family, brand-new Google's free and well-designed font, is
   too big. For example NotoSansCJK-Regular.ttc is 17MB.
 - DroidSansFallbackFull doesn't include Korean Hangul characters.

Thanks,
- -- 
Kenshi Muto
kmuto@debian.org
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