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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
          "http://www.w3.org/TR/html4/loose.dtd">

<title>FreeType Tutorial / I</title>
</head>

<body>

<div id="top"
     class="bar">
  <h1><a href="http://freetype.org/index.html">FreeType</a>
    Tutorial&nbsp;/&nbsp;I</h1>
</div>

<div id="simple-glyph-loading">
          <h2>I. Simple Glyph Loading</h2>

<h3 id="section-1">1. Header Files</h3>

<p>The following are instructions required to compile an
            application that uses the FreeType&nbsp;2 library.</p>

<ol>
            <li class="emph">
              <p>Locate the FreeType&nbsp;2 <code>include</code>
                directory.</p>

<p>You have to add it to your compilation include
                path.</p>

<p>In Unix-like environments you can run the
                <code>freetype-config</code> script with
                the <code>--cflags</code> option to retrieve the
                appropriate compilation flags.  This script can also
                be used to check the version of the library that is
                installed on your system, as well as the required
                librarian and linker flags.</p>

<p>An alternative solution is <code>pkg-config</code>;
                say</p>

<pre>
pkg-config --cflags freetype2</pre>

<p>to get the compilation flags.</p>
            </li>

<li class="emph">
              <p>Include the file named <code>ft2build.h</code>.</p>

<p>It contains various macro declarations that are later
                used to <code>#include</code> the appropriate public
                FreeType&nbsp;2 header files.</p>
            </li>

<li class="emph">
              <p>Include the main FreeType&nbsp;2 API header file.</p>

<p>You should do that using the
                macro <code>FT_FREETYPE_H</code>, like in the
                following example.</p>

<pre>
#include &lt;ft2build.h&gt;
#include FT_FREETYPE_H</pre>

<p><code>FT_FREETYPE_H</code> is a special macro defined
                in file <code>ftheader.h</code>.  It contains some
                installation-specific macros to name other public
                header files of the FreeType&nbsp;2 API.</p>

<p>You can
                read <a href="../reference/ft2-header_file_macros.html">this
                  section of the FreeType&nbsp;2 API Reference</a> for a
                complete listing of the header macros.</p>
            </li>
          </ol>

<p>The use of macros in <code>#include</code> statements is
            ANSI-compliant.  It is used for several reasons.</p>

<ul>
            <li>It avoids conflicts with (deprecated) FreeType 1.x
              public header files.</li>

<li>The macro names are not limited to the DOS 8.3 file
              naming limit; names
              like <code>FT_MULTIPLE_MASTERS_H</code>
              or <code>FT_SFNT_NAMES_H</code> are a lot more readable
              and explanatory than the real file names
              <code>ftmm.h</code> and <code>ftsnames.h</code>.</li>

<li>It allows special installation tricks that will not be
              discussed here.</li>
          </ul>

<h3 id="section-2">2. Library Initialization</h3>

<p>To initialize the FreeType library, create a variable of
            type <a href="../reference/ft2-base_interface.html#FT_Library"><code>FT_Library</code></a>
            named, for example, <code>library</code>, and call the
            function <a href="../reference/ft2-base_interface.html#FT_Init_FreeType"><code>FT_Init_FreeType</code></a>.</p>

<pre>
#include &lt;ft2build.h&gt;
#include FT_FREETYPE_H

FT_Library  library;

...

error = FT_Init_FreeType( &amp;library );
if ( error )
{
  ... an error occurred during library initialization ...
}</pre>

<p>This function is in charge of</p>

<ul>
            <li>creating a new instance of the FreeType&nbsp;2 library
              and setting the handle <code>library</code> to it,
              and</li>

<li>loading each module that FreeType knows about in the
              library.  Among others, your new <code>library</code>
              object is able to handle TrueType, Type&nbsp;1,
              CID-keyed &amp; OpenType/CFF fonts gracefully.</li>
          </ul>

<p>As you can see, the function returns an error code, like
            most other functions of the FreeType API.  An error code
            of&nbsp;0 (also known
            as <code>FT_Err_Ok</code>) <em>always</em> means that the
            operation was successful; otherwise, the value describes
            the error, and <code>library</code> is set to NULL.</p>

<p>A list of all FreeType error codes can be found in
            file <code>fterrdef.h</code>.</p>

<h3 id="section-3">3. Loading a Font Face</h3>

<p>Create a new <code>face</code> object by
            calling <a href="../reference/ft2-base_interface.html#FT_New_Face"><code>FT_New_Face</code></a>.
            A <em>face</em> describes a given typeface and style.  For
            example, &lsquo;Times New Roman Regular&rsquo; and
            &lsquo;Times New Roman Italic&rsquo; correspond to two
            different faces.</p>

<pre>
FT_Library  library;   <span class="comment">/* handle to library     */</span>
FT_Face     face;      <span class="comment">/* handle to face object */</span>

error = FT_Init_FreeType( &amp;library );
if ( error ) { ... }

error = FT_New_Face( library,
                     "/usr/share/fonts/truetype/arial.ttf",
                     0,
                     &amp;face );
if ( error == FT_Err_Unknown_File_Format )
{
  ... the font file could be opened and read, but it appears
  ... that its font format is unsupported
}
else if ( error )
{
  ... another error code means that the font file could not
  ... be opened or read, or that it is broken...
}</pre>

<p>As you can certainly imagine, <code>FT_New_Face</code>
            opens a font file, then tries to extract one face from it.
            Its parameters are as follows.</p>

<dl>
            <dt>library</dt>
            <dd>A handle to the FreeType library instance where the
              face object is created.</dd>

<dt>filepathname</dt>
            <dd>The font file pathname (a standard C string).</dd>

<dt>face_index</dt>
            <dd>
              <p>Certain font formats allow several font faces to be
                embedded in a single file.</p>

<p>This index tells which face you want to load.  An
                error is returned if its value is too large.</p>

<p>Index&nbsp;0 always works, though.</p>
            </dd>

<dt>face</dt>
            <dd>
              <p>A <em>pointer</em> to the handle that is set to
                describe the new face object.</p>

<p>It is set to NULL in case of error.</p>
            </dd>
          </dl>

<p>To know how many faces a given font file contains, set
            <code>face_index</code> to&nbsp;<code>-1</code>, then
            check the value of <code>face-&gt;num_faces</code>, which
            indicates how many faces are embedded in the font
            file.</p>

<h4>b. From Memory</h4>

<p>In the case where you have already loaded the font file
            into memory, you can similarly create a new face object
            for it by
            calling <a href="../reference/ft2-base_interface.html#FT_New_Memory_Face"><code>FT_New_Memory_Face</code></a>.</p>

<pre>
FT_Library  library;   <span class="comment">/* handle to library     */</span>
FT_Face     face;      <span class="comment">/* handle to face object */</span>

error = FT_Init_FreeType( &amp;library );
if ( error ) { ... }

error = FT_New_Memory_Face( library,
                            buffer,    <span class="comment">/* first byte in memory */</span>
                            size,      <span class="comment">/* size in bytes        */</span>
                            0,         <span class="comment">/* face_index           */</span>
                            &amp;face );
if ( error ) { ... }</pre>

<p>As you can see, <code>FT_New_Memory_Face</code> takes a
            pointer to the font file buffer and its size in bytes
            instead of a file pathname.  Other than that, it has
            exactly the same semantics as
            <code>FT_New_Face</code>.</p>

<p>Note that you must not deallocate the font file buffer
            before calling
            <a href="../reference/ft2-base_interface.html#FT_Done_Face"><code>FT_Done_Face</code></a>.</p>

<h4>c. From Other Sources (Compressed Files, Network,
            etc.)</h4>

<p>There are cases where using a file pathname or preloading
            the file into memory is not sufficient.  With
            FreeType&nbsp;2, it is possible to provide your own
            implementation of I/O routines.</p>

<p>This is done through
            the <a href="../reference/ft2-base_interface.html#FT_Open_Face"><code>FT_Open_Face</code></a>
            function, which can be used to open a new font face with a
            custom input stream, select a specific driver for opening,
            or even pass extra parameters to the font driver when
            creating the object.  We advise you to look up
            the <a href="../reference/ft2-toc.html">FreeType&nbsp;2
            reference manual</a> in order to learn how to use it.</p>

<h3 id="section-4">4. Accessing the Face Data</h3>

<p>A <em>face object</em> models all information that
            globally describes the face.  Usually, this data can be
            accessed directly by dereferencing a handle, like
            in <code>face&minus;&gt;num_glyphs</code>.</p>

<p>The complete list of available fields is in
            the <a href="../reference/ft2-base_interface.html#FT_FaceRec"><code>FT_FaceRec</code></a>
            structure description.  However, we describe here a few of
            them in more detail.</p>

<dl>
            <dt>num_glyphs</dt>
            <dd>This variable gives the number of <em>glyphs</em>
              available in the font face.  A glyph is a character
              image, nothing more – it thus doesn't necessarily
              correspond to a <em>character code</em>.</dd>

<dt>face_flags</dt>
            <dd>A 32-bit integer containing bit flags that describe
              some face properties.  For example, the flag
              <code>FT_FACE_FLAG_SCALABLE</code> indicates that the
              face's font format is scalable and that glyph images can
              be rendered for all character pixel sizes.  For more
              information on face flags, please read
              the <a href="../reference/ft2-base_interface.html#FT_FACE_FLAG_XXX">FreeType&nbsp;2
              API Reference</a>.</dd>

<dt>units_per_EM</dt>
            <dd>This field is only valid for scalable formats (it is
              set to&nbsp;0 otherwise).  It indicates the number of
              font units covered by the EM.</dd>

<dt>num_fixed_sizes</dt>
            <dd>This field gives the number of embedded bitmap strikes
              in the current face.  A <em>strike</em> is a series of
              glyph images for a given character pixel size.  For
              example, a font face could include strikes for pixel
              sizes 10, 12, and&nbsp;14.  Note that even scalable font
              formats can have embedded bitmap strikes!</dd>

<dt>available_sizes</dt>
            <dd>
              <p>A pointer to an array
                of <a href="../reference/ft2-base_interface.html#FT_Bitmap_Size"><code>FT_Bitmap_Size</code></a>
                elements.  Each <code>FT_Bitmap_Size</code> indicates
                the horizontal and vertical <em>character pixel
                sizes</em> for each of the strikes that are present in
                the face.</p>

<p class="warning">Note that, generally speaking, these
                are <em>not</em> the <em>cell size</em> of the bitmap
                strikes.</p>
            </dd>
          </dl>

<h3 id="section-5">5. Setting the Current Pixel Size</h3>

<p>FreeType&nbsp;2 uses <em>size objects</em> to model all
            information related to a given character size for a given
            face.  For example, a size object holds the value of
            certain metrics like the ascender or text height,
            expressed in 1/64th of a pixel, for a character size of
            12&nbsp;points (however, those values are rounded to
            integers, i.e., multiples of 64).</p>

<p>When the <code>FT_New_Face</code> function is called (or
            one of its siblings), it <em>automatically</em> creates a
            new size object for the returned face.  This size object
            is directly accessible as
            <code>face&minus;&gt;size</code>.</p>

<p class="note">NOTE: A single face object can deal with one
            or more size objects at a time; however, this is something
            that few programmers really need to do.  We have thus
            decided to make this feature available through additional
            functions.</p>

<p>When a new face object is created, all elements are set
            to&nbsp;0 during initialization.  To populate the
            structure with sensible values, you should
            call <a href="../reference/ft2-base_interface.html#FT_Set_Char_Size"><code>FT_Set_Char_Size</code></a>.
            Here is an example, setting the character size to 16pt for
            a 300&times;300dpi device:</p>

<pre>
error = FT_Set_Char_Size(
          face,    <span class="comment">/* handle to face object           */</span>
          0,       <span class="comment">/* char_width in 1/64th of points  */</span>
          16*64,   <span class="comment">/* char_height in 1/64th of points */</span>
          300,     <span class="comment">/* horizontal device resolution    */</span>
          300 );   <span class="comment">/* vertical device resolution      */</span></pre>

<p>Some notes.</p>

<ul>
            <li>The character widths and heights are specified in
              1/64th of points.  A point is a <em>physical</em>
              distance, equaling 1/72th of an inch.  Normally, it is
              not equivalent to a pixel.</li>

<li>Value of&nbsp;0 for the character width means
              &lsquo;same as character height&rsquo;, value of&nbsp;0
              for the character height means &lsquo;same as character
              width&rsquo;.  Otherwise, it is possible to specify
              different character widths and heights.</li>

<li>The horizontal and vertical device resolutions are
              expressed in <em>dots-per-inch</em>, or <em>dpi</em>.
              Standard values are 72 or 96&nbsp;dpi for display
              devices like the screen.  The resolution is used to
              compute the character pixel size from the character
              point size.</li>

<li>Value of&nbsp;0 for the horizontal resolution means
              &lsquo;same as vertical resolution&rsquo;, value
              of&nbsp;0 for the vertical resolution means &lsquo;same
              as horizontal resolution&rsquo;.  If both values are
              zero, 72&nbsp;dpi is used for both dimensions.</li>

<li>The first argument is a handle to a face object, not a
              size object.</li>
          </ul>

<p>This function computes the (possibly fractional)
            character pixel size that corresponds to the character
            width and height and device resolutions.  A common acronym
            for the pixel size is <em>ppem</em> (pixel per em).</p>

<p>If you want to specify the (integer) pixel sizes
            yourself, you can call
            <a href="../reference/ft2-base_interface.html#FT_Set_Pixel_Sizes"><code>FT_Set_Pixel_Sizes</code></a>.</p>

<pre>
error = FT_Set_Pixel_Sizes(
          face,   <span class="comment">/* handle to face object */</span>
          0,      <span class="comment">/* pixel_width           */</span>
          16 );   <span class="comment">/* pixel_height          */</span></pre>

<p>This example sets the character pixel sizes to
            16&times;16&nbsp;pixels.  As previously, a value of&nbsp;0
            for one of the dimensions means &lsquo;same as the
            other&rsquo;.</p>

<p>Note that both functions return an error code.  Usually,
            an error occurs with a fixed-size font format (like FNT or
            PCF) when trying to set the pixel size to a value that is
            not listed in the <code>face-&gt;fixed_sizes</code>
            array.</p>

<p>Be aware that fractional ppem values are not always
            supported.  For example, the native bytecode engine for
            hinting TrueType fonts (TTFs) only supports integer ppem
            values, and FreeType rounds fractional ppem values
            accordingly.</p>

<h3 id="section-6">6. Loading a Glyph Image</h3>

<h4>a. Converting a Character Code Into a Glyph Index</h4>

<p>Normally, an application wants to load a glyph image
            based on its <em>character code</em>, which is a unique
            value that defines the character for a
            given <em>encoding</em>.  For example, code&nbsp;65 (0x41)
            represents character &lsquo;A&rsquo; in ASCII
            encoding.</p>

<p>A face object contains one or more tables, called
            <em>charmaps</em>, to convert character codes to glyph
            indices.  For example, most older TrueType fonts contain
            two charmaps: One is used to convert Unicode character
            codes to glyph indices, the other one is used to convert
            Apple Roman encoding to glyph indices.  Such fonts can
            then be used either on Windows (which uses Unicode) and
            old MacOS versions (which use Apple Roman).  Note also
            that a given charmap might not map to all the glyphs
            present in the font.</p>

<p>By default, when a new face object is created, FreeType
            tries to select a Unicode charmap.  It emulates a Unicode
            charmap if the font doesn't contain such a charmap, based
            on glyph names.  Note that it is possible that the
            emulation misses glyphs if glyph names are non-standard.
            For some fonts like symbol fonts, no Unicode emulation is
            possible at all.</p>

<p>Later on we will describe how to look for specific
            charmaps in a face.  For now, we assume that the face
            contains at least a Unicode charmap that was selected
            during a call to <code>FT_New_Face</code>.  To convert a
            Unicode character code to a font glyph index, we use
            <a href="../reference/ft2-base_interface.html#FT_Get_Char_Index"><code>FT_Get_Char_Index</code></a>.</p>

<pre>
glyph_index = FT_Get_Char_Index( face, charcode );</pre>

<p>This code line looks up the glyph index corresponding to
            the given <code>charcode</code> in the charmap that is
            currently selected for the face.  You should use the
            UTF-32 representation form of Unicode; for example, if you
            want to load character U+1F028, use value 0x1F028 as the
            value for <code>charcode</code>.

<p>If no charmap was selected, the function returns
            the charcode.</p>

<p>Note that this is one of the rare FreeType functions that
            do not return an error code.  However, when a given
            character code has no glyph image in the face,
            value&nbsp;0 is returned.  By convention, it always
            corresponds to a special glyph image called
            the <em>missing glyph</em>, which is commonly displayed as
            a box or a space.</p>

<h4>b. Loading a Glyph From the Face</h4>

<p>Once you have a glyph index, you can load the
            corresponding glyph image.  The latter can be stored in
            various formats within the font file.  For fixed-size
            formats like FNT or PCF, each image is a bitmap.  Scalable
            formats like TrueType or CFF use vectorial shapes
            (<em>outlines</em>) to describe each glyph.  Some formats
            may have even more exotic ways of representing glyphs
            (e.g., MetaFont – but this format is not supported).
            Fortunately, FreeType&nbsp;2 is flexible enough to support
            any kind of glyph format through a simple API.</p>

<p>The glyph image is always stored in a special object called a
            <em>glyph slot</em>.  As its name suggests, a glyph slot
            is a container that is able to hold one glyph image at a
            time, be it a bitmap, an outline, or something else.  Each
            face object has a single glyph slot object that can be
            accessed as <code>face-&gt;glyph</code>.  Its fields are
            explained by
            the <a href="../reference/ft2-base_interface.html#FT_GlyphSlotRec"><code>FT_GlyphSlotRec</code></a>
            structure documentation.</p>

<p>Loading a glyph image into the slot is performed by
            calling <a href="../reference/ft2-base_interface.html#FT_Load_Glyph"><code>FT_Load_Glyph</code></a>.</p>

<pre>
error = FT_Load_Glyph(
          face,          <span class="comment">/* handle to face object */</span>
          glyph_index,   <span class="comment">/* glyph index           */</span>
          load_flags );  <span class="comment">/* load flags, see below */</span></pre>

<p>The <code>load_flags</code> value is a set of bit flags
            to indicate some special operations.  The default value
            <code>FT_LOAD_DEFAULT</code> is&nbsp;0.</p>

<p>This function tries to load the corresponding glyph image
            from the face.</p>

<ul>
            <li>If a bitmap is found for the corresponding glyph and
              pixel size, it is loaded into the slot.  Embedded
              bitmaps are always favoured over native image formats,
              because we assume that they are higher-quality versions
              of the same glyph.  This can be changed by using
              the <code>FT_LOAD_NO_BITMAP</code> flag.</li>

<li>Otherwise, a native image for the glyph is loaded.  It
              is also scaled to the current pixel size, as well as
              hinted for certain formats like TrueType and
              Type&nbsp;1.</li>
          </ul>

<p>The
            field <code>face&minus;&gt;glyph&minus;&gt;format</code>
            describes the format used for storing the glyph image in
            the slot.  If it is
            not <code>FT_GLYPH_FORMAT_BITMAP</code>, one can
            immediately convert it to a bitmap
            through <a href="../reference/ft2-base_interface.html#FT_Render_Glyph"><code>FT_Render_Glyph</code></a>.</p>

<pre>
error = FT_Render_Glyph( face-&gt;glyph,   <span class="comment">/* glyph slot  */</span>
                         render_mode ); <span class="comment">/* render mode */</span></pre>

<p>The parameter <code>render_mode</code> is a set of bit
            flags to specify how to render the glyph image.
            <code>FT_RENDER_MODE_NORMAL</code>, the default, renders
            an anti-aliased coverage bitmap with 256 gray levels (also
            called a <em>pixmap</em>), as this is the default.  You
            can alternatively use <code>FT_RENDER_MODE_MONO</code> if
            you want to generate a 1-bit monochrome bitmap.  More
            values are available for
            the <a href="../reference/ft2-base_interface.html#FT_Render_Mode"><code>FT_Render_Mode</code></a>
            enumeration value.</p>

<p>Once you have a bitmapped glyph image, you can access it
            directly through <code>glyph-&gt;bitmap</code> (a simple
            descriptor for bitmaps or pixmaps), and position it
            through <code>glyph-&gt;bitmap_left</code> and
            <code>glyph-&gt;bitmap_top</code>.  For optimal rendering
            on a screen the bitmap should be used as an alpha channel
            in linear blending with gamma correction.</p>

<p>Note that <code>bitmap_left</code> is the horizontal
            distance from the current pen position to the leftmost
            border of the glyph bitmap, while <code>bitmap_top</code>
            is the vertical distance from the pen position (on the
            baseline) to the topmost border of the glyph
            bitmap.  <em>It is positive to indicate an upwards
            distance</em>.</p>

<h4>c. Using Other Charmaps</h4>

<p>As said before, when a new face object is created, it
            looks for a Unicode charmap and select it.  The currently
            selected charmap can be accessed
            via <code>face-&gt;charmap</code>.  This field is NULL if
            no charmap is selected, which typically happens when you
            create a new <code>FT_Face</code> object from a font file
            that doesn't contain a Unicode charmap (which is rather
            infrequent today).</p>

<p>There are two ways to select a different charmap with
            FreeType.  It's easiest if the encoding you need already
            has a corresponding enumeration defined
            in <code>FT_FREETYPE_H</code>, for
            example <code>FT_ENCODING_BIG5</code>.  In this case, you
            can call
            <a href="../reference/ft2-base_interface.html#FT_Select_Charmap"><code>FT_Select_Charmap</code></a>.</p>

<pre>
error = FT_Select_Charmap(
          face,               <span class="comment">/* target face object */</span>
          FT_ENCODING_BIG5 ); <span class="comment">/* encoding           */</span></pre>

<p>Another way is to manually parse the list of charmaps for
            the face; this is accessible through the
            fields <code>num_charmaps</code> and
            <code>charmaps</code> (notice the &lsquo;s&rsquo;) of the
            face object.  As you could expect, the first is the number
            of charmaps in the face, while the second is <em>a table
            of pointers to the charmaps</em> embedded in the face.</p>

<p>Each charmap has a few visible fields to describe it more
            precisely.  The most important ones are
            <code>charmap-&gt;platform_id</code>
            and <code>charmap-&gt;encoding_id</code>, defining a pair
            of values that describe the charmap in a rather generic
            way: Each value pair corresponds to a given encoding.  For
            example, the pair (3,1) corresponds to Unicode.  The list
            is defined in the OpenType specification; you can also use
            the file <code>FT_TRUETYPE_IDS_H</code>, which defines
            several helpful constants to deal with them.  Note that we
            use the OpenType enumeration values for non-OpenType fonts
            also (by defining additional constants where
            necessary).</p>

<p>To select a specific encoding, you need to find a
            corresponding value pair in the specification, then look
            for it in the charmaps list.</p>

<pre>
FT_CharMap  found = 0;
FT_CharMap  charmap;
int         n;

for ( n = 0; n &lt; face-&gt;num_charmaps; n++ )
{
  charmap = face-&gt;charmaps[n];
  if ( charmap-&gt;platform_id == my_platform_id &amp;&amp;
       charmap-&gt;encoding_id == my_encoding_id )
  {
    found = charmap;
    break;
  }
}

if ( !found ) { ... }

<span class="comment">/* now, select the charmap for the face object */</span>
error = FT_Set_Charmap( face, found );
if ( error ) { ... }</pre>

<p>Once a charmap has been selected, either through
            <code>FT_Select_Charmap</code>
            or <a href="../reference/ft2-base_interface.html#FT_Set_Charmap"><code>FT_Set_Charmap</code></a>,
            it is used by all subsequent calls
            to <code>FT_Get_Char_Index</code>.</p>

<h4>d. Glyph Transformations</h4>

<p>It is possible to specify an affine transformation with
            <a href="../reference/ft2-base_interface.html#FT_Set_Transform"><code>FT_Set_Transform</code></a>,
            to be applied to glyph images when they are loaded.  Of
            course, this only works for scalable (vectorial) font
            formats.</p>

<pre>
error = FT_Set_Transform(
          face,       <span class="comment">/* target face object    */</span>
          &amp;matrix,    <span class="comment">/* pointer to 2x2 matrix */</span>
          &amp;delta );   <span class="comment">/* pointer to 2d vector  */</span></pre>

<p>This function sets the current transformation for a given
            face object.  Its second parameter is a pointer to an
            <a href="../reference/ft2-basic_types.html#FT_Matrix"><code>FT_Matrix</code></a>
            structure that describes a 2&times;2 affine matrix.  The
            third parameter is a pointer to
            an <a href="../reference/ft2-basic_types.html#FT_Vector"><code>FT_Vector</code></a>
            structure, describing a two-dimensional vector that
            translates the glyph image <em>after</em> the 2&times;2
            transformation.</p>

<p>Note that the matrix pointer can be set to NULL, in which
            case the identity transformation is used.  Coefficients of
            the matrix are otherwise in 16.16 fixed-point units.</p>

<p>The vector pointer can also be set to NULL (in which case
            a delta of (0,0) is used).  The vector coordinates are
            expressed in 1/64th of a pixel (also known as 26.6
            fixed-point numbers).</p>

<p class="warning">The transformation is applied to every
            glyph that is loaded through <code>FT_Load_Glyph</code>
            and is <em>completely independent of any hinting
            process</em>.  This means that you won't get the same
            results if you load a glyph at the size of 24&nbsp;pixels,
            or a glyph at the size of 12&nbsp;pixels scaled by&nbsp;2
            through a transformation, because the hints are computed
            differently (except if you have disabled hints).</p>

<p>If you ever need to use a non-orthogonal transformation
            with optimal hints, you first have to decompose your
            transformation into a scaling part and a rotation/shearing
            part.  Use the scaling part to compute a new character
            pixel size, then the other one to call
            <code>FT_Set_Transform</code>.  This is explained in more
            detail in part&nbsp;II of this tutorial.</p>

<p class="warning">Rotation usually disables hinting.</p>

<p>Loading a glyph bitmap with a non-identity transformation
            works; the transformation is ignored in this case.</p>

<h3 id="section-7">7. Simple Text Rendering</h3>

<p>We now present a simple example to render a string of
            8-bit Latin-1 text, assuming a face that contains a
            Unicode charmap.</p>

<p>The idea is to create a loop that loads one glyph image
            on each iteration, converts it to a pixmap, draws it on
            the target surface, then increments the current pen
            position.</p>

<h4 id="basic-code">a. Basic Code</h4>

<p>The following code performs our simple text rendering
            with the functions previously described.</p>

<pre>
FT_GlyphSlot  slot = face-&gt;glyph;  <span class="comment">/* a small shortcut */</span>
int           pen_x, pen_y, n;

... initialize library ...
... create face object ...
... set character size ...

pen_x = 300;
pen_y = 200;

for ( n = 0; n &lt; num_chars; n++ )
{
  FT_UInt  glyph_index;

<span class="comment">/* retrieve glyph index from character code */</span>
  glyph_index = FT_Get_Char_Index( face, text[n] );

<span class="comment">/* load glyph image into the slot (erase previous one) */</span>
  error = FT_Load_Glyph( face, glyph_index, FT_LOAD_DEFAULT );
  if ( error )
    continue;  <span class="comment">/* ignore errors */</span>

<span class="comment">/* convert to an anti-aliased bitmap */</span>
  error = FT_Render_Glyph( face-&gt;glyph, FT_RENDER_MODE_NORMAL );
  if ( error )
    continue;

<span class="comment">/* now, draw to our target surface */</span>
  my_draw_bitmap( &amp;slot-&gt;bitmap,
                  pen_x + slot-&gt;bitmap_left,
                  pen_y - slot-&gt;bitmap_top );

<span class="comment">/* increment pen position */</span>
  pen_x += slot-&gt;advance.x >> 6;
  pen_y += slot-&gt;advance.y >> 6; <span class="comment">/* not useful for now */</span>
}</pre>

<p>This code needs a few explanations.</p>

<ul>
            <li>We define a handle named <code>slot</code> that points
              to the face object's glyph slot.  (The
              type <a href="../reference/ft2-base_interface.html#FT_GlyphSlot"><code>FT_GlyphSlot</code></a>
              is a pointer).  That is a convenience to avoid using
              <code>face-&gt;glyph-&gt;XXX</code> every time.</li>

<li>We increment the pen position with the vector
              <code>slot-&gt;advance</code>, which correspond to the
              glyph's <em>advance width</em> (also known as
              its <em>escapement</em>).  The advance vector is
              expressed in 1/64th of pixels, and is truncated to
              integer pixels on each iteration.</li>

<li>The function <code>my_draw_bitmap</code> is not part
              of FreeType but must be provided by the application to
              draw the bitmap to the target surface.  In this example,
              it takes a pointer to
              an <a href="../reference/ft2-basic_types.html#FT_Bitmap"><code>FT_Bitmap</code></a>
              descriptor and the position of its top-left corner as
              arguments.  For ideal rendering on a screen this
              function should perform linear blending with gamma
              correction, using the bitmap as an alpha channel.</li>

<li>The value of <code>slot-&gt;bitmap_top</code> is
              positive for an <em>upwards</em> vertical distance.
              Assuming that the coordinates taken
              by <code>my_draw_bitmap</code> use the opposite
              convention (increasing&nbsp;Y corresponds to downwards
              scanlines), we subtract it from <code>pen_y</code>,
              instead of adding to it.</li>
          </ul>

<h4>b.Refined code</h4>

<p>The following code is a refined version of the example
            above.  It uses features and functions of FreeType that
            have not yet been introduced, and which are explained
            below.</p>

<pre>
FT_GlyphSlot  slot = face-&gt;glyph;  <span class="comment">/* a small shortcut */</span>
FT_UInt       glyph_index;
int           pen_x, pen_y, n;

... initialize library ...
... create face object ...
... set character size ...

pen_x = 300;
pen_y = 200;

for ( n = 0; n &lt; num_chars; n++ )
{
  <span class="comment">/* load glyph image into the slot (erase previous one) */</span>
  error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
  if ( error )
    continue;  <span class="comment">/* ignore errors */</span>

<span class="comment">/* increment pen position */</span>
  pen_x += slot-&gt;advance.x >> 6;
}</pre>

<p>We have reduced the size of our code, but it does exactly
            the same thing.</p>

<ul>
            <li>We use the
              function <a href="../reference/ft2-base_interface.html#FT_Load_Char"><code>FT_Load_Char</code></a>
              instead of <code>FT_Load_Glyph</code>.  As you probably
              imagine, it is equivalent to
              calling <code>FT_Get_Char_Index</code>, then
              <code>FT_Load_Glyph</code>.</li>

<li>
              <p>We do not use <code>FT_LOAD_DEFAULT</code> for the
                loading mode, but the bit
                flag <code>FT_LOAD_RENDER</code>.  It indicates that
                the glyph image must be immediately converted to an
                anti-aliased bitmap.  This is of course a shortcut
                that avoids calling <code>FT_Render_Glyph</code>
                explicitly but is strictly equivalent.</p>

<p>Note that you can also specify that you want a
                monochrome bitmap instead by using the
                additional <code>FT_LOAD_MONOCHROME</code> load
                flag.</p>
            </li>
          </ul>

<h4 id="transformed-text">c. More Advanced Rendering</h4>

<p>Let us try to render transformed text now (for example
            through a rotation).  We can do this
            using <code>FT_Set_Transform</code>.</p>

<pre>
FT_GlyphSlot  slot;
FT_Matrix     matrix;              <span class="comment">/* transformation matrix */</span>
FT_UInt       glyph_index;
FT_Vector     pen;                 <span class="comment">/* untransformed origin */</span>
int           n;

... initialize library ...
... create face object ...
... set character size ...

slot = face-&gt;glyph;                <span class="comment">/* a small shortcut */</span>

<span class="comment">/* set up matrix */</span>
matrix.xx = (FT_Fixed)( cos( angle ) * 0x10000L );
matrix.xy = (FT_Fixed)(-sin( angle ) * 0x10000L );
matrix.yx = (FT_Fixed)( sin( angle ) * 0x10000L );
matrix.yy = (FT_Fixed)( cos( angle ) * 0x10000L );

<span class="comment">/* the pen position in 26.6 cartesian space coordinates */</span>
<span class="comment">/* start at (300,200)                                   */</span>
pen.x = 300 * 64;
pen.y = ( my_target_height - 200 ) * 64;

for ( n = 0; n &lt; num_chars; n++ )
{
  <span class="comment">/* set transformation */</span>
  FT_Set_Transform( face, &amp;matrix, &amp;pen );

<span class="comment">/* load glyph image into the slot (erase previous one) */</span>
  error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
  if ( error )
    continue;  <span class="comment">/* ignore errors */</span>

<span class="comment">/* now, draw to our target surface (convert position) */</span>
  my_draw_bitmap( &amp;slot-&gt;bitmap,
                  slot-&gt;bitmap_left,
                  my_target_height - slot-&gt;bitmap_top );

<span class="comment">/* increment pen position */</span>
  pen.x += slot-&gt;advance.x;
  pen.y += slot-&gt;advance.y;
}</pre>

<p>Some remarks.</p>

<ul>
            <li>We now use a vector of type <code>FT_Vector</code> to
              store the pen position, with coordinates expressed as
              1/64th of pixels, hence a multiplication.  The position
              is expressed in cartesian space.</li>

<li>Glyph images are always loaded, transformed, and
              described in the cartesian coordinate system within
              FreeType (which means that increasing&nbsp;Y corresponds
              to upper scanlines), unlike the system typically used
              for bitmaps (where the topmost scanline has
              coordinate&nbsp;0).  We must thus convert between the
              two systems when we define the pen position, and when we
              compute the topleft position of the bitmap.</li>

<li>We set the transformation on each glyph to indicate
              the rotation matrix as well as a delta that moves the
              transformed image to the current pen position (in
              cartesian space, not bitmap space).  As a consequence,
              the values of <code>bitmap_left</code>
              and <code>bitmap_top</code> correspond to the bitmap
              origin in target space pixels.  We thus don't
              add <code>pen.x</code> or <code>pen.y</code> to their
              values when calling <code>my_draw_bitmap</code>.</li>

<li>The advance width is always returned transformed,
              which is why it can be directly added to the current pen
              position.  Note that it is <em>not</em> rounded this
              time.</li>
          </ul>

<p>A complete source code example can be found
            <a href="example1.c">here</a>.</p>

<p>It is important to note that, while this example is a bit
            more complex than the previous one, it is strictly
            equivalent for the case where the transformation is the
            identity.  Hence it can be used as a replacement (but a
            more powerful one).</p>

<p>The still present few shortcomings will be explained, and
            solved, in the next part of this tutorial.</p>
        </div>

<div class="updated">
          <p>Last update: 13-Feb-2018</p>
        </div>
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