Re: Calculating the maximum size of a rendered bitmap

[David Turner]

Hi Kevin,

> Kevin Dance a écrit :
> 
> I am using the function calls "FT_Load_Glyph(Face,Index,FT_LOAD_DEFAULT)" and 
> "FT_Render_Glyph(Face->glyph, ft_render_mode_normal)" to render a
> given glyph into a bitmap of type "FT_Bitmap". However, what I need to do is 
> to know the maximum possible size that the bitmap can be before hand.
> Can this be achieved without simply looping throught all of the glyphs and 
> rendering them during the initialisation phase of my program, since this
> will obviously take time. Is there a quick was to do this calculation?
> 

There is no simple way to do that other than parsing all glyphs.
Note that you could however use, for scalable formats, the face's
global bounding box to obtain an _idea_ of the largest "character cell".

I'm using the word _idea_ because you cannot simply scale the bbox to
the current pixel size because of hinting. Maybe if you add a one pixel
border to it, you would have something meaningful, but there is no
guarantee.

> Alternatively, if I have to loop through all of the glyphs then I can 
> determine the total number of glyphs by using "Face->num_glyphs".  However, I
> have tried to render all glyphs from 0 to "Face->num_glyphs - 1" but my 
> program crashes. How can I tell whether I can render a given glyph index and
> has anyone got any code to do this calculation successfully?
> 
I suppose you're using Beta8. It contains a bug in the auto-hinter that causes
crashes when certain fonts are used. Please use the current snapshot, it believe
it is rock-solid :-)

Cheers,

- David