Re: FT Cache Subsystem: Custom caches

[Alexei Podtelezhnikov]

Hi Kelvin

If you only interested in subpixels shifts and intend to cache 3
positions, you can achieve using LCD rendering and
https://freetype.org/freetype2/docs/reference/ft2-lcd_rendering.html#ft_library_setlcdgeometry.
It is apparent that LCD rendering is essentially 3 traditional
antialiased bitmaps produced for shifted outlines and stacked
together. Therefore, you have it already for 1/3-pixel shifts by
default. Because everything is periodic, you can continue with the LCD
output and clever reading frame shifts for subpixel positioning too.

Theoretically, this should work.

There is also 
https://freetype.org/freetype2/docs/reference/ft2-sizing_and_scaling.html#ft_set_transform
.  Perhaps you should wrap it into
https://freetype.org/freetype2/docs/reference/ft2-cache_subsystem.html#ftc_face_requester.

Alexei

Re: FT Cache Subsystem: Custom caches

[takase1121 via FreeType users]

Hi, sorry for the confusion; I think its better if I explain my current 
approach first:

1. I create a FTC_Manager, FTC_CMapCache and FTC_ImageCache, and set them up.
2. I query a glyph ID from FTC_CMapCache.
3. I get a glyph image (almost always an outline in my case) from 
FTC_ImageCache.
4. I copy the FT_Glyph and perform translation and other transformation on it.
5. I rasterize the transformed FT_Glyph.
6. I use the rasterized bitmap.

I wasn't able to cache the rasterized glyph because FTC_SBitCache doesn't 
support transformations.

I am looking to do one of these things:

1. Being able to apply transformations in FTC_SBitCache.

The main reason I can't use FTC_SBitCache is that I need to modify the outline. 
I need to translate it for subpixel positioning, italicize, embolden and apply 
other transformations before rasterizing. I think this is a niche use case, so 
I'm not fully expecting the cache subsystem to support this.

2. Being able to extend / implement my own cache types.

Alternatively, I want to be able to implement a custom cache type, based on 
FTC_Manager. Based on the draft document in the previous email, this was 
possible, but didn't make it to release. This new cache would behave like 
FTC_SBitCache, but supports the various operations I need to do on the glyph 
outlines before rendering.

I hope this clears things up. I was looking for ways to avoid rolling my own 
cache if possible. Thanks.

Kelvin.

Re: FT Cache Subsystem: Custom caches

[Werner LEMBERG]

> I'm trying to use FreeType cache subsystem to render glyphs. I tried
> using FTC_SBitCache but I need to modify the outline before
> rendering (translate and transform) so I could only use
> FTC_ImageCache, modify the outline and render it.
> 
> Is there a way to extend the cache mechanism to create my own cache
> that supports all these features?

Extend in which way?  It's not clear to me what you want to cache...


Werner