RE: [Freetype] rendering a string, using outlines, in mono

[Turner, David]

> hello,
> 
> i want to render a string, on 1-bit bitmap, using the outlines of the
> glyph (FT_Outline_Get_Bitmap). I have 2 questions:
> 
> 1) when i render the string in a big bitmap (say, the BBox, 
> which i have computed before rendering), only the last character is 
> rendered. It seems that at each call of FT_Outline_Get_Bitmap, this one clear 
> the bitmap that i give to it. Is it the case ? Does it only create 
> "standalone" bitmap
> ? (from the doc: "Renders an outline within a bitmap. The  outline's image
> is simply OR-ed to the target bitmap")
> 
It's difficult to answer without seeing your code, but all I can say is the
following:

  - the bitmap _should_ be or-ed to the target surface
  - you can check it rather easily, just fill your target bitmap
    with a random value (e.g. 0x55), then draw in it. The result
    will tell you quite easily if something was overwritten :-)

> 2) the second question is related to the translation of a outline. I
> wanted to translate the characters of the strind, with FT_Outline_Translate, 
> but, it seems that if i give the vector in pixel unit, it's not sufficient. 
> I have to multiply the value of the offset that i give (that is, the pen 
> position, 
> expressed) by something like 4. I don't understand why this factor arises 
> (why 4, 
> and not 1<<6, as the coords of an outline is expressed in 26.6 format)
> 
That's strange, because:

- FT_Outline_Translate only performs addition on the vector coordinates
  stored in the outline. It doesn't know anything about scaling

- by default, hinted/scaled outlines are stored with 1/64 pixels accuracy,
  which means that you need to multiply pixel distances by 64 before
  passing them to FT_Outline_Translate.

- unscaled outlines are expressed in "EM" units, so you should express
  your translation in the EM space to call FT_Outline_Translate

I don't see where your 4 factor comes from. Did you scale the outlines
yourself ?

Hope this helps,

- David Turner
- The FreeType Project  (www.freetype.org)