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|
<!doctype html public "-//w3c//dtd html 4.0 transitional//en"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">
<meta name="Author"
content="David Turner">
<title>FreeType 2 Tutorial</title>
</head>
<body text="#000000"
bgcolor="#FFFFFF"
link="#0000EF"
vlink="#51188E"
alink="#FF0000">
<h1 align=center>
FreeType 2.0 Tutorial<br>
Step 1 -- simple glyph loading
</h1>
<h3 align=center>
© 2000 David Turner
(<a href="mailto:david@freetype.org">david@freetype.org</a>)<br>
© 2000 The FreeType Development Team
(<a href="http://www.freetype.org">www.freetype.org</a>)
</h3>
<center>
<table width="75%">
<tr><td>
<hr>
<h2>
Introduction
</h2>
<p>This is the first part of the FreeType 2 tutorial. It will
teach you to do the following:</p>
<ul>
<li>initialize the library</li>
<li>open a font file by creating a new face object</li>
<li>select a character size in points or in pixels</li>
<li>load a single glyph image and convert it to a bitmap</li>
<li>render a very simple string of text</li>
<li>render a rotated string of text easily</li>
</ul>
<hr>
<h3>
1. Header files
</h3>
<p>To include the main FreeType header file, say</p>
<font color="blue">
<pre>
#include <freetype/freetype.h></pre>
</font>
<p>in your application code. Note that other files are available in the
FreeType include directory, most of them being included by
<tt>freetype.h</tt> and other (internal) files. Some of them will be
described later in this tutorial.</p>
<hr>
<h3>
2. Initialize the library
</h3>
<p>Simply create a variable of type <tt>FT_Library</tt> named, for
example, <tt>library</tt>, and call the function
<tt>FT_Init_FreeType()</tt> as in</p>
<font color="blue">
<pre>
#include <freetype/freetype.h>
FT_Library library;
...
{
...
error = FT_Init_FreeType( &library );
if ( error )
{
... an error occurred during library initialization ...
}
}</pre>
</font>
<p>This function is in charge of the following:</p>
<ul>
<li>
Creating a new instance of the FreeType 2 library, and set the
handle <tt>library</tt> to it.
</li>
<li>
Load each module that FreeType knows about in the library. This
means that by default, your new <tt>library</tt> object is able to
handle TrueType, Type 1, Windows FON, CID-keyed & OpenType/CFF
fonts gracefully.
</li>
</ul>
<p>As you can see, the function returns an error code, like most others
in the FreeType API. An error code of 0 <em>always</em> means that
the operation was successful; otherwise, the value describes the error,
and <tt>library</tt> is set to <tt>NULL</tt>.</p>
<hr>
<h3>
3. Load a font face
</h3>
<h4>
a. From a font file
</h4>
<p>Create a new <em>face</em> object by calling
<tt>FT_New_Face()</tt>. A <em>face</em> describes a given typeface
and style. For example, "Times New Roman Regular" and "Times New
Roman Italic" correspond to two different faces.</p>
<font color="blue">
<pre>
FT_Library library; /* handle to library */
FT_Face face; /* handle to face object */
error = FT_Init_FreeType( &library );
if ( error ) { ... }
error = FT_New_Face( library,
"/usr/share/fonts/truetype/arial.ttf",
0,
&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>
</font>
<p>As you can certainly imagine, <tt>FT_New_Face()</tt> opens a font
file, then tries to extract one face from it. Its parameters are</p>
<table cellpadding=5>
<tr valign="top">
<td>
<tt>library</tt>
</td>
<td>
<p>A handle to the FreeType library instance where the face
object is created</p>
</td>
</tr>
<tr valign="top">
<td>
<tt>filepathname</tt>
</td>
<td>
<p>The font file pathname (a standard C string).</p>
</td>
</tr>
<tr valign="top">
<td>
<tt>face_index</tt>
</td>
<td>
<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 will
be returned if its value is too large.</p>
<p>Index 0 always work though.</p>
</td>
</tr>
<tr valign="top">
<td>
<tt>face</tt>
</td>
<td>
<p>A <em>pointer</em> to the handle that will be set to describe
the new face object.</p>
<p>It is set to <tt>NULL</tt> in case of error.</p>
</td>
</tr>
</table>
<p>To know how many faces a given font file contains, load its first
face (use <tt>face_index</tt>=0), then check the value of
<tt>face->num_faces</tt> 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 in memory,
you can similarly create a new face object for it by calling
<tt>FT_New_Memory_Face()</tt> as in</p>
<font color="blue">
<pre>
FT_Library library; /* handle to library */
FT_Face face; /* handle to face object */
error = FT_Init_FreeType( &library );
if ( error ) { ... }
error = FT_New_Memory_Face( library,
buffer, /* first byte in memory */
size, /* size in bytes */
0, /* face_index */
&face );
if ( error ) { ... }</pre>
</font>
<p>As you can see, <tt>FT_New_Memory_Face()</tt> 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
<tt>FT_New_Face()</tt>.</p>
<h4>
c. From other sources (compressed files, network, etc.)
</h4>
<p>There are cases where using a file pathname or preloading the file
in memory is not sufficient. With FreeType 2, it is possible to
provide your own implementation of I/O routines.</p>
<p>This is done through the <tt>FT_Open_Face()</tt> 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 refer to the
FreeType 2 API reference in order to learn how to use it.</p>
<p>Note that providing a custom stream might also be used to access a
TrueType font embedded in a Postscript Type 42 wrapper.</p>
<hr>
<h3>
4. Accessing face contents
</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</p>
<table cellpadding=5>
<tr valign="top">
<td>
<tt>face->num_glyphs</tt>
</td>
<td>
<p>Gives the number of <em>glyphs</em> available in the font face.
A glyph is simply a character image. It doesn't necessarily
correspond to a <em>character code</em> though.</p>
</td>
</tr>
<tr valign="top">
<td>
<tt>face->flags</tt>
</td>
<td>
<p>A 32-bit integer containing bit flags used to describe some
face properties. For example, the flag
<tt>FT_FACE_FLAG_SCALABLE</tt> is used to indicate 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="#">FreeType 2 API Reference</a>.</p>
</td>
</tr>
<tr valign="top">
<td>
<tt>face->units_per_EM</tt>
</td>
<td>
<p>This field is only valid for scalable formats (it is set
to 0 otherwise). It indicates the number of font units
covered by the EM.</p>
</td>
</tr>
<tr valign="top">
<td>
<tt>face->num_fixed_sizes</tt>
</td>
<td>
<p>This field gives the number of embedded bitmap <em>strikes</em>
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 14. Note
that even scalable font formats can have embedded bitmap
strikes!</p>
</td>
</tr>
<tr valign="top">
<td>
<tt>face->fixed_sizes</tt>
</td>
<td>
<p>This is a pointer to an array of <tt>FT_Bitmap_Size</tt>
elements. Each <tt>FT_Bitmap_Size</tt> indicates the horizontal
and vertical <em>pixel sizes</em> for each of the strikes that are
present in the face.</p>
</td>
</tr>
</table>
<p>For a complete listing of all face properties and fields, please read
the <a href="#">FreeType 2 API Reference</a>.<p>
<hr>
<h3>
5. Setting the current pixel size
</h3>
<p>FreeType 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 will hold the value of certain metrics like the ascender or text
height, expressed in 1/64th of a pixel, for a character size of
12 points.</p>
<p>When the <tt>FT_New_Face()</tt> function is called (or one of its
cousins), it <em>automatically</em> creates a new size object for the
returned face. This size object is directly accessible as
<tt>face->size</tt>.</p>
<p><em>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 have decided to simplify the API for the most common use
(i.e. one size per face), while keeping this feature available through
additional functions.</em></p>
<p>When a new face object is created, its size object defaults to the
character size of 10 pixels (both horizontally and vertically) for
scalable formats. For fixed-sizes formats, the size is more or less
undefined, which is why you must set it before trying to load a
glyph.</p>
<p>To do that, simply call <tt>FT_Set_Char_Size()</tt>. Here is an
example where the character size is set to 16pt for a 300x300 dpi
device:</p>
<font color="blue">
<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>
</font>
<p>You will notice that</p>
<ul>
<li>
The character width and heights are specified in 1/64th of points.
A point is a <em>physical</em> distance, equaling 1/72th of an inch;
it is not a pixel.
</li>
<li>
Horizontal and vertical device resolutions are expressed in
<em>dots-per-inch</em>, or <em>dpi</em>. You can use 72 or
96 dpi for display devices like the screen. The resolution is
used to compute the character pixel size from the character point
size.
</li>
<li>
A value of 0 for the character width means <em>same as
character height</em>, a value of 0 for the character height
means <em>same as character width</em>. Otherwise, it is possible
to specify different char widths and heights.
</li>
<li>
Using a value of 0 for the horizontal or vertical resolution
means 72 dpi, which is the default.
</li>
<li>
The first argument is a handle to a face object, not a size object.
This behaviour must be seen as a convenience.
</li>
</ul>
<p>This function computes the character pixel size that corresponds to
the character width and height and device resolutions. However, if you
want to specify the pixel sizes yourself, you can simply call
<tt>FT_Set_Pixel_Sizes()</tt>, as in</p>
<font color="blue">
<pre>
error = FT_Set_Pixel_Sizes(
face, /* handle to face object */
0, /* pixel_width */
16 ); /* pixel_height */</pre>
</font>
<p>This example will set the character pixel sizes to 16x16 pixels.
As previously, a value of 0 for one of the dimensions means
<em>same as the other</em>.</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
<tt>face->fixed_sizes</tt> array.</p>
<hr>
<h3>
6. Loading a glyph image
</h3>
<h4>
a. Converting a character code into a glyph index
</h4>
<p>Usually, 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, the character
code 65 in ASCII encoding represents letter `A'.</p>
<p>A face object contains one or more tables, called
<em>charmaps</em>, that are used to convert character codes to glyph
indices. For example, most TrueType fonts contain two charmaps. One
is used to convert Unicode character codes to glyph indices, the other
is used to convert Apple Roman encoding into glyph indices. Such
fonts can then be used either on Windows (which uses Unicode) and
Macintosh (which uses Apple Roman usually). 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, it lists all the
charmaps contained in the font face and selects the one that supports
Unicode character codes if it finds one. Otherwise, it tries to find
support for Latin-1, then ASCII.</p>
<p>We will describe later how to look for specific charmaps in a face.
For now, we will assume that the face contains at least a Unicode
charmap that was selected during <tt>FT_New_Face()</tt>. To convert a
Unicode character code to a font glyph index, we use
<tt>FT_Get_Char_Index()</tt> as in</p>
<font color="blue">
<pre>
glyph_index = FT_Get_Char_Index( face, charcode );</pre>
</font>
<p>This will look up the glyph index corresponding to the given
<tt>charcode</tt> in the charmap that is currently selected for the
face.
<p>Note that this is one of the rare FreeType functions that do not
return an error code. If a given character code has no glyph image in
the face, the value 0 is returned. By convention, it always
corresponds to a special glyph image called the <em>missing
glyph</em>, which usually is represented 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 Type 1 use vectorial shapes,
named <em>outlines</em>, to describe each glyph. Some formats may have
even more exotic ways of representing glyphs (e.g. MetaFont).
Fortunately, FreeType 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 <tt>face->glyph</tt>.</p>
<p>Loading a glyph image into the slot is performed by calling
<tt>FT_Load_Glyph()</tt> as in</p>
<font color="blue">
<pre>
error = FT_Load_Glyph(
face, /* handle to face object */
glyph_index, /* glyph index */
load_flags ); /* load flags, see below */</pre>
</font>
<p>The <tt>load_flags</tt> value is a set of bit flags used to
indicate some special operations. The default value
<tt>FT_LOAD_DEFAULT</tt> is 0.</p>
<p>This function will try to load the corresponding glyph image from
the face. Basically, this means that</p>
<ul>
<li>
<p>If a bitmap is found for the corresponding glyph and pixel
size, it will be loaded into the slot. Embedded bitmaps are
always favored over native image formats, because we assume that
they are higher-quality versions of the same glyph. This can be
changed by using the <tt>FT_LOAD_NO_BITMAP</tt> flag.</p>
</li>
<li>
<p>Otherwise, a native image for the glyph will be loaded. It
will also be scaled to the current pixel size as well as hinted
for certain formats like TrueType and Type 1.</p>
</li>
</ul>
<p>The field <tt>glyph->format</tt> describes the format used to store
the glyph image in the slot. If it is not
<tt>ft_glyph_format_bitmap</tt>, it is possible to immedialy convert
it to a bitmap through <tt>FT_Render_Glyph()</tt>, as in</p>
<font color="blue">
<pre>
error = FT_Render_Glyph(
face->glyph, /* glyph slot */
render_mode ); /* render mode */</pre>
</font>
<p>The parameter <tt>render_mode</tt> specifies how to render the
glyph image. Set it <tt>ft_render_mode_normal</tt> to render a
high-quality anti-aliased (256 gray levels) bitmap. You can
alternatively use <tt>ft_render_mode_mono</tt> if you want to generate
a 1-bit monochrome bitmap.</p>
<p>Once you have a bitmapped glyph image, you can access it directly
through <tt>glyph->bitmap</tt> (a simple bitmap descriptor), and
position it with <tt>glyph->bitmap_left</tt> and
<tt>glyph->bitmap_top</tt>.</p>
<p>Note that <tt>bitmap_left</tt> is the horizontal distance from the
current pen position to the left-most border of the glyph bitmap,
while <tt>bitmap_top</tt> is the vertical distance from the pen
position (on the baseline) to the top-most border of the glyph bitmap.
<em>It is positive to indicate an upwards distance</em>.</p>
<p>The second part of the tutorial describes the contents of a glyph
slot and how to access specific glyph information (including
metrics).</p>
<h4>
c. Using other charmaps
</h4>
<p>As said before, when a new face object is created, it will look for
a Unicode, Latin-1, or ASCII charmap and select it. The currently
selected charmap is accessed via <tt>face->charmap</tt>. This field
is <tt>NULL</tt> if no charmap is selected, which typically happens
when you create a new <tt>FT_Face</tt> object from a font file that
doesn't contain an ASCII, Latin-1, or Unicode charmap (rare
stuff).</p>
<p>There are two ways to select a different charmap with
FreeType 2. The easiest is if the encoding you need already has
a corresponding enumeration defined in <tt>freetype/freetype.h</tt>,
as <tt>ft_encoding_big5</tt>. In this case, you can simply call
<tt>FT_Select_CharMap()</tt> as in</p>
<font color="blue"><pre>
error = FT_Select_CharMap(
face, /* target face object */
ft_encoding_big5 ); /* encoding */</pre>
</font>
<p>Another way is to manually parse the list of charmaps for the face;
this is accessible through the fields <tt>num_charmaps</tt> and
<tt>charmaps</tt> (notice the final 's') of the face object. As
expected, 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 used to describe it more
precisely. Mainly, one will look at <tt>charmap->platform_id</tt> and
<tt>charmap->encoding_id</tt> which define a pair of values that can
be used to describe the charmap in a rather generic way.</p>
<p>Each value pair corresponds to a given encoding. For example, the
pair (3,1) corresponds to Unicode (on the Windows platform). A list
of such pairs is defined in the TrueType specification, but you can
also use the file <tt><freetype/ttnameid.h></tt> which defines
several helpful constants to deal with them.</p>
<p>Note that some pid/eid pairs are <em>artificial</em>; such values
have been created by FreeType to identify platforms resp. encodings
not covered by the original TrueType specification.</p>
<p>To look up a specific encoding you need to find a corresponding
value pair in the specification, then look for it in the
<tt>charmaps</tt> list. Bear in mind that some encodings correspond
to several values pairs (yes, it's a real mess, but blame Apple and
Microsoft on such stupidity). Here some code to do it:</p>
<font color="blue">
<pre>
FT_CharMap found = 0;
FT_CharMap charmap;
int n;
for ( n = 0; n < face->num_charmaps; n++ )
{
charmap = face->charmaps[n];
if ( charmap->platform_id == my_platform_id &&
charmap->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>
</font>
<p>Once a charmap has been selected, either through
<tt>FT_Select_CharMap()</tt> or <tt>FT_Set_CharMap()</tt>, it is used
by all subsequent calls to <tt>FT_Get_Char_Index()</tt>.</p>
<h4>
d. Glyph transformations
</h4>
<p>It is possible to specify an affine transformation to be applied to
glyph images when they are loaded. Of course, this will only work for
scalable (vectorial) font formats.</p>
<p>To do that, simply call <tt>FT_Set_Transform()</tt>, as in</p>
<font color="blue">
<pre>
error = FT_Set_Transform(
face, /* target face object */
&matrix, /* pointer to 2x2 matrix */
&delta ); /* pointer to 2d vector */</pre>
</font>
<p>This function will set the current transformation for a given face
object. Its second parameter is a pointer to an <tt>FT_Matrix</tt>
structure that describes a 2x2 affine matrix. The third
parameter is a pointer to an <tt>FT_Vector</tt> structure that
describes a simple 2d vector that is used to translate the glyph
image <em>after</em> the 2x2 transformation.</p>
<p>Note that the matrix pointer can be set to <tt>NULL</tt>, in which
case the identity transformation will be used. Coefficients of the
matrix are otherwise in 16.16 fixed float units.</p>
<p>The vector pointer can also be set to <tt>NULL</tt> in which case a
delta vector of (0,0) will be used. The vector coordinates are
expressed in 1/64th of a pixel (also known as 26.6 fixed floats).</p>
<p><em>The transformation is applied to every glyph that is loaded
through <tt>FT_Load_Glyph()</tt> and is <b>completely independent of
any hinting process.</b> This means that you won't get the same
results if you load a glyph at the size of 24 pixels, or a glyph
at the size at 12 pixels scaled by 2 through a
transformation, because hints will have been computed differently
(unless hints have been disabled, of course).</em></p>
<p>If you ever need to use a non-orthogonal transformation with
optimal hints, you first need 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
<tt>FT_Set_Transform()</tt>. This is explained in details in a later
section of this tutorial.</p>
<p>Note also that loading a glyph bitmap with a non-identity
transformation will produce an error.</p>
<hr>
<h3>
7. Simple text rendering
</h3>
<p>We will now present a very simple example used 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 will, on each iteration, load one
glyph image, convert it to an anti-aliased bitmap, draw it on the target
surface, then increment the current pen position.</p>
<h4>
a. basic code
</h4>
<p>The following code performs our simple text rendering with the
functions previously described.</p>
<font color="blue">
<pre>
FT_GlyphSlot slot = face->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 < 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->glyph, ft_render_mode_normal );
if ( error ) continue;
/* now, draw to our target surface */
my_draw_bitmap( &slot->bitmap,
pen_x + slot->bitmap_left,
pen_y - slot->bitmap_top );
/* increment pen position */
pen_x += slot->advance.x >> 6;
pen_y += slot->advance.y >> 6; /* not useful for now */
}</pre>
</font>
<p>This code needs a few explanations:</p>
<ul>
<li>
We define a handle named <tt>slot</tt> that points to the face
object's glyph slot. (The type <tt>FT_GlyphSlot</tt> is a
pointer.) This is a convenience to avoid using
<tt>face->glyph->XXX</tt> every time.
</li>
<li>
We increment the pen position with the vector
<tt>slot->advance</tt>, which corresponds 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 <tt>my_draw_bitmap()</tt> 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
<tt>FT_Bitmap</tt> descriptor and the position of its top-left
corner as arguments.
</li>
<li>
The value of <tt>slot->bitmap_top</tt> is positive for an
<em>upwards</em> vertical distance. Assuming that the coordinates
taken by <tt>my_draw_bitmap()</tt> use the opposite convention
(increasing Y corresponds to downwards scanlines), we substract it
to <tt>pen_y</tt> instead of adding 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 2 that have not yet been
introduced, and which will be explained below.</p>
<font color="blue">
<pre>
FT_GlyphSlot slot = face->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 < 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 */
/* now, draw to our target surface */
my_draw_bitmap( &slot->bitmap,
pen_x + slot->bitmap_left,
pen_y - slot->bitmap_top );
/* increment pen position */
pen_x += slot->advance.x >> 6;
}</pre>
</font>
<p>We have reduced the size of our code, but it does exactly the same
thing.</p>
<ul>
<li>
<p>We use the function <tt>FT_Load_Char()</tt> instead of
<tt>FT_Load_Glyph()</tt>. As you probably imagine, it is
equivalent to calling <tt>FT_Get_Char_Index()</tt> followed by
<tt>FT_Get_Load_Glyph()</tt>.</p>
</li>
<li>
<p>We do not use <tt>FT_LOAD_DEFAULT</tt> for the loading mode but
the bit flag <tt>FT_LOAD_RENDER</tt>. It indicates that the glyph
image must be immediately converted to an anti-aliased bitmap.
This is of course a shortcut that avoids calling
<tt>FT_Render_Glyph()</tt> explicitly but is strictly
equivalent.</p>
<p>Note that you can also specify that you want a monochrome
bitmap by using the <tt>FT_LOAD_MONOCHROME</tt> load flag
instead.</p>
</li>
</ul>
<h4>c. more advanced rendering</h4>
<p>We now render transformed text (for example through a rotation).
To do that we use <tt>FT_Set_Transform()</tt>:</p>
<font color="blue">
<pre>
FT_GlyphSlot slot = face->glyph; /* a small shortcut */
FT_Matrix matrix; /* transformation matrix */
FT_UInt glyph_index;
FT_Vector pen; /* untransformed origin */
int n;
.. initialize library ..
.. create face object ..
.. set character size ..
/* 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 */
pen.x = 300 * 64;
pen.y = ( my_target_height - 200 ) * 64;
for ( n = 0; n < num_chars; n++ )
{
/* set transformation */
FT_Set_Transform( face, &matrix, &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( &slot->bitmap,
slot->bitmap_left,
my_target_height - slot->bitmap_top );
/* increment pen position */
pen.x += slot->advance.x;
pen.y += slot->advance.y;
}</pre>
</font>
<p>Notes:</p>
<ul>
<li>
We now use a vector of type <tt>FT_Vector</tt> 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>
In FreeType, glyph images are always loaded, transformed, and
described in the cartesian coordinate system (which means that
increasing Y corresponds to upper scanlines), unlike the
system typically used for bitmaps (where the top-most scanline has
coordinate 0). We must thus convert between the two systems
when we define the pen position, and when we compute the top-left
position of the bitmap.
</li>
<li>
We apply the transformation matrix on each glyph to indicate
rotation as well as a delta vector that will move the transformed
image to the current pen position (in cartesian space, not bitmap
space).
</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>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>It has, however, a few shortcomings that we will explain, and
solve, in the next part of this tutorial.</p>
<hr>
<h3>
Conclusion
</h3>
<p>In this first section, you have learned the basics of FreeType 2
as well as sufficient knowledge how to render rotated text.</p>
<p>The next part will dive into more details of the API in order to let
you access glyph metrics and images directly, how to deal with scaling,
hinting, kerning, etc.</p>
<p>The third part will discuss issues like modules, caching, and a few
other advanced topics like how to use multiple size objects with a
single face.</p>
</td></tr>
</table>
</center>
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