Re: [ft] Fw: freetype cache and glyph metrics

[Michael Plitkins]

Thanks. This may well get me moving forward. I do indeed need to
measure the horiBearingY because I am trying to line up type of
different sizes to get the presentation that we need. Measuring a few
sample characters will be adequate. Using the rendered bitmap still
won't give me a way to calculate the descender though (all I will know
is the actual full height of the rendered glyph).

I knew that the FT_Load_Glyph(), was bogus, but it was my last ditch attempt.

Using FTC_CMapCache_Lookup() is on list my too.

Many thanks and I will report how this turns out.

Michael

On Wed, Sep 29, 2010 at 8:34 AM, Brady Duga <address@hidden> wrote:
> Well, I am not entirely sure what you want to do. Using horiBearingY as the
> ascender seems weird - do you really want to use glyph metrics for line
> metrics? Or do you really need the ascender/descender info for every glyph?
> In any case, you shouldn't be calling FT_Load_Glyph when using the cache
> system. Instead, you let the cache subsytem make that call using the load
> flags you supply to FTC_ImageCache_LookupScaler(). That gives you an
> FT_Glyph which you can use for basic glyph metrics. Specifically the
> "advance" vector of that struct tells you how far to move to account for
> this glyph. In a more interesting case, you would pass FT_LOAD_RENDER to the
> cache subsystem, which should make the returned glyph be an FT_BitmapGlyph.
> That in turn gives you the left/top coordinates for the actual bitmap, plus
> an FT_Bitmap struct you can use for more information. Once you have the top
> and left values, you can essentially calculate the horibearingX/Y, though
> you may not need to bother. The nice thing about using the cache is, in most
> cases rendering is fast (already cached). It's only a problem if you plan to
> measure a *lot* of glyphs that you don't plan to render. Of course, in that
> case there isn't much point in using the cache at all.
> You might also want to consider caching the char map
> using FTC_CMapCache_Lookup instead of FT_Get_Char_Index.
> --Brady
>
>
> On Sep 28, 2010, at 11:30 PM, Werner LEMBERG wrote:
>
> Please help this guy.
>
>
>    Werner
>
> From: Michael Plitkins <address@hidden>
> Date: September 28, 2010 9:50:48 PM PDT
> To: address@hidden
> Subject: freetype cache and glyph metrics
>
>
> Hello Werner,
>
> I have been using freetype for some time and have come to my first
> stumbling block: When using the image and font face caches, how can I
> get the the full metrics of a glyph (metrics.horiBearingY, etc.)? It
> seems that information is only available from the FT_GlyphSlotRec in
> the face itself. When using the cache APIs all of my attempts to get
> at the FT_Glyph_Metrics have yielded inconsistent results. Here is one
> of my latest attempts:
>
> void nlGfxContext :: GetGlyphMetrics(nlULONG aHeight, char aGlyph,
> nlFontMetrics *aOutMetrics)
> {
>    if ((mFont != NULL) && (aOutMetrics != NULL))
>    {
>        FT_Face         font;
>        FTC_ScalerRec   scaler;
>
>        scaler.face_id = mFont;
>        scaler.width = 0;
>        scaler.height = aHeight;
>        scaler.pixel = 1;
>        scaler.x_res = 0;
>        scaler.y_res = 0;
>
>        font = mGlobals->LookupFontID(mFont);
>
>        if (font != NULL)
>        {
>            FTC_ImageCache  icache = mGlobals->GetFontImageCache();
>            FT_Glyph        glyph;
>            FTC_Node        node;
>            FT_UInt         charidx = FT_Get_Char_Index(font, aGlyph);
>            FT_Error        err;
>
>            err = FTC_ImageCache_LookupScaler(icache, &scaler,
> FT_LOAD_DEFAULT, charidx, &glyph, &node);
>
>            FT_Load_Glyph(font, charidx, FT_LOAD_DEFAULT);
>
>            if (err == FT_Err_Ok)
>            {
>                aOutMetrics->mHeight = font->glyph->metrics.height >> 6;
>                aOutMetrics->mAscender = font->glyph->metrics.horiBearingY >>
> 6;
>                aOutMetrics->mDescender = -(aOutMetrics->mHeight -
> aOutMetrics->mAscender);
>                aOutMetrics->mMaxAdvance =
> font->glyph->metrics.horiAdvance >> 6;
>
>                FTC_Node_Unref(node, mGlobals->GetFontCacheManager());
>            }
>        }
>    }
> }
>
> This is my horrible attempt to use the image cache scaler to get the
> glyph that i want at the size that i want and somehow get the glyph
> metrics to be set as i want as part of the FT_Load_Glyph(). It seems
> like it shouldn't work and it doesn't.
>
> How does one get the metrics for an individual glyph and use the
> caching subsystems at the same time?
>
> I apologize in advance if this has been answered somewhere out on the
> internet, but I was unable to find it.
>
> Many thanks.
>
> Michael Plitkins
>
>
> _______________________________________________
> Freetype mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/freetype
>
>