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

[Michael Plitkins]

Trust me, this is a very special case of character at a time rendering
with some character tops or baselines aligned to neighboring glyph top
edges, etc. as opposed to a run of text. If the bitmap height - top
will get me a descender, then I am all done.

Michael

On Wed, Sep 29, 2010 at 11:12 AM, Brady Duga <address@hidden> wrote:
> Again, I really don't think you want descenders per-glyph. So, say you want 
> to draw some text on a line. If we consider the upper-left of the screen to 
> be 0,0 with y increasing as we go down, and you want to draw a line whose 
> baseline is at y=100, then you:
>
> set x to 0
> set y to 100
> for every glyph:
>  get cached glyph info
>  draw bitmap at x+glyph.left, y - glyph.top
>  set x to x + glyph.advance.x
>
> This will place all your glyphs on the same baseline. If you really want to 
> know how much of the glyph extends below the line, then it is just the bitmap 
> height minus top.
>
> --Brady
>
> On Sep 29, 2010, at 11:04 AM, Michael Plitkins wrote:
>
>> Yes it does work, but there is still no way to get the descender. The
>> FT_GlyphRec already has some of the FT_Glyph_Metrics information in
>> the form of the advance. Why doesn't the FT_GlyphRec contain the
>> remaining information? Memory concerns? Performance?
>>
>> Thanks again for help and suggestions.
>>
>> Michael
>>
>> On Wed, Sep 29, 2010 at 9:50 AM, Michael Plitkins
>> <address@hidden> wrote:
>>> 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
>>>>
>>>>
>>>
>
>