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Bug 4307 - Improve SDL_ttf glyph cache system
Summary: Improve SDL_ttf glyph cache system
Status: RESOLVED FIXED
Alias: None
Product: SDL_ttf
Classification: Unclassified
Component: misc (show other bugs)
Version: unspecified
Hardware: x86_64 Linux
: P2 normal
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2018-10-12 13:47 UTC by Sylvain
Modified: 2018-11-06 14:29 UTC (History)
0 users

See Also:

Attachments
patch (2.36 KB, patch)
2018-10-12 13:48 UTC, Sylvain 		Details | Diff
patch updated (4.34 KB, patch)
2018-11-03 07:08 UTC, Sylvain 		Details | Diff
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Description Sylvain 2018-10-12 13:47:01 UTC 
There are many glyph cache misses with SDL_ttf because it use characters itselves as keys. It's more efficient to use FT indexes as keys.
Comment 1 Sylvain 2018-10-12 13:48:39 UTC 
Created attachment 3368 [details]
patch
Comment 2 Sylvain 2018-10-19 13:07:19 UTC 
Update: I was too optimistic when I said it would reduce number of collisions when caching glyphs, hence, be more efficient.
In fact, I took into account the initialisation of cache, because it calls "Flush_Glyph" the first time for Glyph cache system. I was mistaken.

In the end, it seems to be the same. Maybe a little bit less of collision with Index, when using Arabic or Chinese, but this is minimal and that can also be my test-case.



But, in favour of the patch
===========================

Using Index instead of Glyph is a better option to ease the integration of a text shaping engine into SDL_ttf (like in bug 3046 and bug 3211). It also doesn't break current SDL_ttf.

This way, SDL_ttf can have in the future a function to render an array of indexes e.g: 
  
    SDL_Surface *TTF_RenderINDEX_Solid(TTF_Font *font, int *indexes, int nb_indexes, SDL_Color fg);

Where (indexes, nb_indexes) would be produced by a text shaping engine.

Having a text shaping engine is essential to render text correctly. To be picky, even English language needs it to render ligatures like "fi".
https://en.wikipedia.org/wiki/Typographic_ligature
https://en.wikipedia.org/wiki/Typographic_ligature#/media/File:Ligatures.svg
Comment 3 Sam Lantinga 2018-11-02 23:49:16 UTC 
Can you rebase this patch on the current code in Mercurial?

Thanks!
Comment 4 Sylvain 2018-11-03 07:08:29 UTC 
Created attachment 3436 [details]
patch updated

I've updated the patch and changed it a little bit. 
(no need to have twice the index in the cache slot!)
Comment 5 Sam Lantinga 2018-11-06 14:29:17 UTC 
Patch added, thanks!
https://hg.libsdl.org/SDL_ttf/rev/1fc2b16737da