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          Can I use FreeType to draw text on a pixmap with arbitrary depth?
        Not directly, as FreeType is a font library, not a
        general-purpose graphics library or text rendering service.
        However, note that the anti-aliased renderer allows you to convert a
        vectorial glyph outline into a list of ‘spans’ (i.e.,
        horizontal pixel segments with the same coverage) that can be
        rendered through user-provided callbacks. By providing the appropriate span callback, you can render
        anti-aliased text to any kind of surface.  You can also use any
        colour, fill pattern or fill image if you want to.  This process is
        called direct rendering.
        
        
    FT_Raster_Params  params;
    FT_Outline        outline;
    ... load vectorial glyph in ‘outline’ ...
    params.flags      = FT_RASTER_FLAG_AA | FT_RASTER_FLAG_DIRECT;
    params.gray_spans = (FT_Raster_Span_Func)your_own_span_function;
    params.user       = your_own_data_pointer;
    error = FT_Outline_Render( library, &outline, ¶ms ); Note that direct rendering is not available with
        monochrome output, as the current renderer uses a two-pass algorithm
        to generate glyphs with correct drop-out control. 
 
          How can I set the colour of text rendered by FreeType?
        Basically, you can't do that, because FreeType is simply a font
        library.  In general, you need to use your favorite graphics library
        to draw the FreeType glyphs with the appropriate colour. Note that for anti-aliased glyphs, you can ‘set the
        colour’ by using direct rendering as described in this answer. 
 
          I set the pixel size to 8×8, but the resulting glyphs are
          larger (or smaller) than that.  Why?
        A lot of people have difficulties to understand this topic, because
        they think of glyphs as fixed-width or fixed-height
        ‘cells’, like those of fonts used in terminals/consoles.
        This assumption is not valid with most ‘modern’ font
        formats, even for bitmapped-based ones like PCF or
        BDF. Be aware that the character size that is set either
        through FT_Set_Char_Size() or FT_Set_Pixel_Sizes()
        isn't directly related to the dimension of the generated glyph
        bitmaps! Rather, the character size is indeed the size of an abstract
        square, called the EM, used by typographers to design
        fonts.  Scaling two distinct fonts to the same character size, be it
        expressed in points or pixels, generally results in bitmaps with
        distinct dimensions! Note that historically, the EM corresponded to the width of a
        capital ‘M’ in Latin typefaces.  However, later
        improvements in typography led to designs that greatly deviate from
        this rule.  Today, it is not possible to connect the EM size to a
        specific font ‘feature’ in a reliable way. 
 
          How can I compute the bounding box of a text string without
          loading its glyphs before?
        This is not possible in general.  Reason is that hinting distorts
        the glyph shape for optimal rasterization, and this process
        sometimes creates outlines which have considerably different
        metrics.  The TrueType format provides the (optional)
        ‘hdmx’ table which contains device horizontal metrics
        for selected pixel sizes, but even here the vertical metrics are
        missing. It is probably best to use both a glyph and a metrics cache to
        avoid recomputation. 
 
          Which anti-aliasing algorithm is used by FreeType 2?
        The algorithm has been specifically designed for FreeType.  It is
        based on ideas that were originally found in the implementation of
        the libArt graphics
        library to compute the exact pixel coverage of a vector
        image with no sub-sampling and filtering. However, these two implementations are radically distinct and use
        vastly different models.  The FreeType 2 renderer is optimized
        specifically for rendering small complex shapes, like glyphs, at
        very high speed while using very few memory.  On the other hand,
        libArt has been designed for general shape and polygon processing,
        especially large ones. The FreeType 2 anti-aliasing renderer is indeed
        faster than the monochrome renderer for small character
        sizes (typically <20 pixels).  The reason is that the
        monochrome renderer must perform two passes on the outline in order
        to perform drop-out control according to the TrueType
        specification. 
 
          When will FreeType 2 support OpenType?
        Well, the engine already reads OpenType/CFF files perfectly.
        What it doesn't do is handling ‘OpenType Layout’
        tables. FreeType 1 comes with a set of extensions that are used to
        load and manage OpenType Layout tables.  It even has a demonstration
        program named ftstrtto to show its capabilities.  However,
        this code is no longer maintained, and we strongly advise to not use
        it. For FreeType 2, we have decided that the layout operations
        provided through these tables are better placed in a specific
        text-layout library like Pango. |