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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>

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

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

You have to add it to your compilation include
 path.

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.

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

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

to get the compilation flags.
 </li>

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

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

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

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

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

<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.

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.
 </li>
 </ol>

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

<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>

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>.

<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>

This function is in charge of

<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>

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>) always means that the
 operation was successful; otherwise, the value describes
 the error, and <code>library</code> is set to NULL.

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

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

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 face 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.

<pre>
FT_Library library; /* handle to library */
FT_Face face; /* handle to face object */

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>

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.

<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>
 Certain font formats allow several font faces to be
 embedded in a single file.

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

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

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

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

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.

<h4>b. From Memory</h4>

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>.

<pre>
FT_Library library; /* handle to library */
FT_Face face; /* handle to face object */

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

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

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>.

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>.

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

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.

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.

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

A face object 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>.

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.

<dl>
 <dt>num_glyphs</dt>
 <dd>This variable gives the number of glyphs
 available in the font face. A glyph is a character
 image, nothing more – it thus doesn't necessarily
 correspond to a character code.</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 strike 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>
 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 character pixel
 sizes for each of the strikes that are present in
 the face.

Note that, generally speaking, these
 are not the cell size of the bitmap
 strikes.
 </dd>
 </dl>

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

FreeType&nbsp;2 uses size objects 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).

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

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.

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:

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

Some notes.

<ul>
 <li>The character widths and heights are specified in
 1/64th of points. A point is a physical
 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 dots-per-inch, or dpi.
 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>

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 ppem (pixel per em).

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>.

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

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;.

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.

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.

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

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

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

A face object contains one or more tables, called
 charmaps, 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.

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.

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>.

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

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>.

If no charmap was selected, the function returns
 the charcode.

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 missing glyph, which is commonly displayed as
 a box or a space.

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

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
 (outlines) 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.

The glyph image is always stored in a special object called a
 glyph slot. 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.

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>.

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

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.

This function tries to load the corresponding glyph image
 from the face.

<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>

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>.

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

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 pixmap), 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.

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.

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. It is positive to indicate an upwards
 distance.

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

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).

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>.

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

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 a table
 of pointers to the charmaps embedded in the face.

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).

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

<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 ) { ... }

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

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>.

<h4>d. Glyph Transformations</h4>

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.

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

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 after the 2&times;2
 transformation.

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.

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).

The transformation is applied to every
 glyph that is loaded through <code>FT_Load_Glyph</code>
 and is completely independent of any hinting
 process. 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).

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.

Rotation usually disables hinting.

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

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

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

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.

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

The following code performs our simple text rendering
 with the functions previously described.

<pre>
FT_GlyphSlot slot = face-&gt;glyph; /* a small shortcut */
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;

/* retrieve glyph index from character code */
 glyph_index = FT_Get_Char_Index( face, text[n] );

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

/* convert to an anti-aliased bitmap */
 error = FT_Render_Glyph( face-&gt;glyph, FT_RENDER_MODE_NORMAL );
 if ( error )
 continue;

/* now, draw to our target surface */
 my_draw_bitmap( &amp;slot-&gt;bitmap,
 pen_x + slot-&gt;bitmap_left,
 pen_y - slot-&gt;bitmap_top );

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

This code needs a few explanations.

<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 advance width (also known as
 its escapement). 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 upwards 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>

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.

<pre>
FT_GlyphSlot slot = face-&gt;glyph; /* a small shortcut */
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++ )
{
 /* load glyph image into the slot (erase previous one) */
 error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
 if ( error )
 continue; /* ignore errors */

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

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

<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>
 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.

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

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

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

<pre>
FT_GlyphSlot slot;
FT_Matrix matrix; /* transformation matrix */
FT_UInt glyph_index;
FT_Vector pen; /* untransformed origin */
int n;

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

slot = face-&gt;glyph; /* a small shortcut */

/* set up matrix */
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 );

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

for ( n = 0; n &lt; num_chars; n++ )
{
 /* set transformation */
 FT_Set_Transform( face, &amp;matrix, &amp;pen );

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

/* now, draw to our target surface (convert position) */
 my_draw_bitmap( &amp;slot-&gt;bitmap,
 slot-&gt;bitmap_left,
 my_target_height - slot-&gt;bitmap_top );

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

Some remarks.

<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 not rounded this
 time.</li>
 </ul>

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

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).

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

<div class="updated">
 Last update: 2-May-2017
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