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<meta name="Author"
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<title>FreeType 2 Tutorial</title>
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<h1 align=center>
FreeType 2 Tutorial<br>
Step 2 — managing glyphs
</h1>
<h3 align=center>
© 2009 David Turner
(<a href="mailto:david@freetype.org">david@freetype.org</a>)<br>
© 2009 The FreeType Development Team
(<a href="http://www.freetype.org">www.freetype.org</a>)
</h3>
<center>
<table width="70%">
<tr><td>
<hr>
<h2>
Introduction
</h2>
<p>This is the second section of the FreeType 2 tutorial. It
describes how to</p>
<ul>
<li>retrieve glyph metrics</li>
<li>easily manage glyph images</li>
<li>retrieve global metrics (including kerning)</li>
<li>render a simple string of text, with kerning</li>
<li>render a centered string of text (with kerning)</li>
<li>render a transformed string of text (with centering)</li>
<li>access metrics in design font units when needed,
and how to scale them to device space</li>
</ul>
<hr>
<h3>
1. Glyph metrics
</h3>
<p>Glyph metrics are, as their name suggests, certain distances
associated with each glyph in order to describe how to use it to layout
text.</p>
<p>There are usually two sets of metrics for a single glyph: Those used
to layout the glyph in horizontal text layouts (Latin, Cyrillic, Arabic,
Hebrew, etc.), and those used to layout the glyph in vertical text
layouts (Chinese, Japanese, Korean, etc.).</p>
<p>Note that only a few font formats provide vertical metrics. You can
test whether a given face object contains them by using the macro
<tt>FT_HAS_VERTICAL</tt>, which is true when appropriate.</p>
<p>Individual glyph metrics can be accessed by first loading the glyph
in a face's glyph slot, then accessing them through the
<tt>face->glyph->metrics</tt> structure, whose type is <a
href="../reference/ft2-base_interface.html#FT_Glyph_Metrics">
<tt>FT_Glyph_Metrics</tt></a>. We will discuss this in more detail
below; for now, we only note that it contains the following fields:</p>
<center><table width="90%" cellpadding=5>
<tr valign=top>
<td>
<tt>width</tt>
</td>
<td>
<p>This is the width of the glyph image's bounding box. It is
independent of the layout direction.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>height</tt>
</td>
<td>
<p>This is the height of the glyph image's bounding box. It is
independent of the layout direction. Be careful not to confuse it
with the ‘height’ field in the <a
href="../reference/ft2-base_interface.html#FT_Size_Metrics">
<tt>FT_Size_Metrics</tt></a> structure.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>horiBearingX</tt>
</td>
<td>
<p>For <em>horizontal text layouts</em>, this is the horizontal
distance from the current cursor position to the leftmost border of
the glyph image's bounding box.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>horiBearingY</tt>
</td>
<td>
<p>For <em>horizontal text layouts</em>, this is the vertical
distance from the current cursor position (on the baseline) to the
topmost border of the glyph image's bounding box.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>horiAdvance</tt>
</td>
<td>
<p>For <em>horizontal text layouts</em>, this is the horizontal
distance used to increment the pen position when the glyph is drawn
as part of a string of text.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>vertBearingX</tt>
</td>
<td>
<p>For <em>vertical text layouts</em>, this is the horizontal
distance from the current cursor position to the leftmost border of
the glyph image's bounding box.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>vertBearingY</tt>
</td>
<td>
<p>For <em>vertical text layouts</em>, this is the vertical distance
from the current cursor position (on the baseline) to the topmost
border of the glyph image's bounding box.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>vertAdvance</tt>
</td>
<td>
<p>For <em>vertical text layouts</em>, this is the vertical distance
used to increment the pen position when the glyph is drawn as part
of a string of text.</p>
</td>
</tr>
</table>
</center>
<p><font color="red">NOTE: As not all fonts do contain vertical
metrics, the values of <tt>vertBearingX</tt>, <tt>vertBearingY</tt> and
<tt>vertAdvance</tt> should not be considered reliable when
<tt>FT_HAS_VERTICAL</tt> is false.</font></p>
<p>The following graphics illustrate the metrics more clearly. First,
for horizontal metrics, where the baseline is the horizontal axis:</p>
<center>
<img src="metrics.png" alt="horizontal layout" width=388 height=253>
</center>
<p>For vertical text layouts, the baseline is vertical, identical to the
vertical axis:</p>
<center>
<img src="metrics2.png" alt="vertical layout" width=294 height=278>
</center>
<p>The metrics found in <tt>face->glyph->metrics</tt> are normally
expressed in 26.6 pixel format (i.e., 1/64th of pixels), unless you use
the <tt>FT_LOAD_NO_SCALE</tt> flag when calling <tt>FT_Load_Glyph</tt>
or <tt>FT_Load_Char</tt>. In this case, the metrics will be expressed
in original font units.</p>
<p>The glyph slot object has also a few other interesting fields that
will ease a developer's work. You can access them through
<tt>face->glyph->xxx</tt>, where <tt>xxx</tt> is one of the
following fields:</p>
<center><table width="90%" cellpadding=5>
<tr valign=top>
<td>
<tt>advance</tt>
</td>
<td>
<p>This field is a <tt>FT_Vector</tt> which holds the transformed
advance for the glyph. That is useful when you are using a transform
through <tt>FT_Set_Transform</tt>, as shown in the rotated text
example of section I. Other than that, its value is
by default (metrics.horiAdvance,0), unless you specify
<tt>FT_LOAD_VERTICAL</tt> when loading the glyph image;
it will then be (0,metrics.vertAdvance)</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>linearHoriAdvance</tt>
</td>
<td>
<p>This field contains the linearly scaled value of the glyph's
horizontal advance width. Indeed, the value of
<tt>metrics.horiAdvance</tt> that is returned in the glyph slot is
normally rounded to integer pixel coordinates (i.e., it will be a
multiple of 64) by the font driver used to load the glyph
image. <tt>linearHoriAdvance</tt> is a 16.16 fixed-point number
that gives the value of the original glyph advance width in
1/65536th of pixels. It can be use to perform pseudo
device-independent text layouts.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>linearVertAdvance</tt>
</td>
<td>
<p>This is the similar to <tt>linearHoriAdvance</tt> but for the
glyph's vertical advance height. Its value is only reliable if the
font face contains vertical metrics.</p>
</td>
</tr>
</table>
</center>
<hr>
<h3>
2. Managing glyph images
</h3>
<p>The glyph image that is loaded in a glyph slot can be converted into
a bitmap, either by using <tt>FT_LOAD_RENDER</tt> when loading it, or by
calling <tt>FT_Render_Glyph</tt>. Each time you load a new glyph image,
the previous one is erased from the glyph slot.</p>
<p>There are situations, however, where you may need to extract this
image from the glyph slot in order to cache it within your application,
and even perform additional transformations and measures on it before
converting it to a bitmap.</p>
<p>The FreeType 2 API has a specific extension which is capable of
dealing with glyph images in a flexible and generic way. To use it, you
first need to include the <a
href="../reference/ft2-header_file_macros.html#FT_GLYPH_H">
<tt>FT_GLYPH_H</tt></a> header file, as in:</p>
<div class="pre">
#include FT_GLYPH_H
</div>
<p>We will now explain how to use the functions defined in this
file:</p>
<h4>
a. Extracting the glyph image:
</h4>
<p>You can extract a single glyph image very easily. Here some code
that shows how to do it:</p>
<div class="pre">
FT_Glyph glyph; <span class="comment">/* a handle to the glyph image */</span>
...
error = FT_Load_Glyph( face, glyph_index, FT_LOAD_NORMAL );
if ( error ) { ... }
error = FT_Get_Glyph( face->glyph, &glyph );
if ( error ) { ... }
</div>
<p>As you see, we have:</p>
<ul>
<li>
<p>Created a variable, named <tt>glyph</tt>, of type <a
href="../reference/ft2-glyph_management.html#FT_Glyph">
<tt>FT_Glyph</tt></a>. This is a handle (pointer) to an
individual glyph image.</p>
</li>
<li>
<p>Loaded the glyph image normally in the face's glyph slot. We
did not use <tt>FT_LOAD_RENDER</tt> because we want to grab a
scalable glyph image, in order to later transform it.</p>
</li>
<li>
<p>Copy the glyph image from the slot into a new <tt>FT_Glyph</tt>
object, by calling <a
href="../reference/ft2-glyph_management.html#FT_Get_Glyph">
<tt>FT_Get_Glyph</tt></a>. This function returns an error code
and sets <tt>glyph</tt>.</p>
</li>
</ul>
<p>It is important to note that the extracted glyph is in the same
format as the original one that is still in the slot. For example,
if we are loading a glyph from a TrueType font file, the glyph image
will really be a scalable vector outline.</p>
<p>You can access the field <tt>glyph->format</tt> if you want to
know exactly how the glyph is modeled and stored. A new glyph object
can be destroyed with a call to <a
href="../reference/ft2-glyph_management.html#FT_Done_Glyph">
<tt>FT_Done_Glyph</tt></a>.</p>
<p>The glyph object contains exactly one glyph image and a 2D vector
representing the glyph's advance in 16.16 fixed-point coordinates.
The latter can be accessed directly as <tt>glyph->advance</tt></p>
<p><font color="red">Note that unlike other FreeType objects, the
library doesn't keep a list of all allocated glyph objects. This
means you have to destroy them yourself instead of relying on
<tt>FT_Done_FreeType</tt> doing all the clean-up.</font></p>
<h4>
b. Transforming & copying the glyph image
</h4>
<p>If the glyph image is scalable (i.e., if <tt>glyph->format</tt>
is not equal to <tt>FT_GLYPH_FORMAT_BITMAP</tt>), it is possible to
transform the image anytime by a call to <a
href="../reference/ft2-glyph_management.html#FT_Glyph_Transform">
<tt>FT_Glyph_Transform</tt></a>.</p>
<p>You can also copy a single glyph image with <a
href="../reference/ft2-glyph_management.html#FT_Glyph_Copy">
<tt>FT_Glyph_Copy</tt></a>. Here is some example code:</p>
<div class="pre">
FT_Glyph glyph, glyph2;
FT_Matrix matrix;
FT_Vector delta;
... load glyph image in `glyph' ...
<span class="comment">/* copy glyph to glyph2 */</span>
error = FT_Glyph_Copy( glyph, &glyph2 );
if ( error ) { ... could not copy (out of memory) ... }
<span class="comment">/* translate `glyph' */</span>
delta.x = -100 * 64; <span class="comment">/* coordinates are in 26.6 pixel format */</span>
delta.y = 50 * 64;
FT_Glyph_Transform( glyph, 0, &delta );
<span class="comment">/* transform glyph2 (horizontal shear) */</span>
matrix.xx = 0x10000L;
matrix.xy = 0.12 * 0x10000L;
matrix.yx = 0;
matrix.yy = 0x10000L;
FT_Glyph_Transform( glyph2, &matrix, 0 );
</div>
<p>Note that the 2×2 transform matrix is always applied to the
16.16 advance vector in the glyph; you thus don't need to recompute
it.</p>
<h4>
c. Measuring the glyph image
</h4>
<p>You can also retrieve the control (bounding) box of any glyph image
(scalable or not) through the <a
href="../reference/ft2-glyph_management.html#FT_Glyph_Get_CBox">
<tt>FT_Glyph_Get_CBox</tt></a> function, as in:</p>
<div class="pre">
FT_BBox bbox;
...
FT_Glyph_Get_CBox( glyph, <em>bbox_mode</em>, &bbox );
</div>
<p>Coordinates are relative to the glyph origin (0,0), using the
y upwards convention. This function takes a special argument,
the <em>bbox mode</em>, to indicate how box coordinates are
expressed.</p>
<p>If the glyph has been loaded with <tt>FT_LOAD_NO_SCALE</tt>,
<tt>bbox_mode</tt> must be set to <tt>FT_GLYPH_BBOX_UNSCALED</tt> to
get unscaled font units in 26.6 pixel format. The value
<tt>FT_GLYPH_BBOX_SUBPIXELS</tt> is another name for this
constant.</p>
<p>Note that the box's maximum coordinates are exclusive, which means
that you can always compute the width and height of the glyph image,
be in in integer or 26.6 pixels, with:</p>
<div class="pre">
width = bbox.xMax - bbox.xMin;
height = bbox.yMax - bbox.yMin;
</div>
<p>Note also that for 26.6 coordinates, if
<tt>FT_GLYPH_BBOX_GRIDFIT</tt> is used as the bbox mode, the
coordinates will also be grid-fitted, which corresponds to</p>
<div class="pre">
bbox.xMin = FLOOR( bbox.xMin )
bbox.yMin = FLOOR( bbox.yMin )
bbox.xMax = CEILING( bbox.xMax )
bbox.yMax = CEILING( bbox.yMax )
</div>
<p>To get the bbox in <em>integer</em> pixel coordinates, set
<tt>bbox_mode</tt> to <tt>FT_GLYPH_BBOX_TRUNCATE</tt>.</p>
<p>Finally, to get the bounding box in grid-fitted pixel coordinates,
set <tt>bbox_mode</tt> to <tt>FT_GLYPH_BBOX_PIXELS</tt>.
<h4>
d. Converting the glyph image to a bitmap
</h4>
<p>You may need to convert the glyph object to a bitmap once you have
conveniently cached or transformed it. This can be done easily with
the <a href="../reference/ft2-glyph_management.html">
<tt>FT_Glyph_To_Bitmap</tt></a> function. It is in charge of
converting any glyph object into a bitmap, as in:</p>
<div class="pre">
FT_Vector origin;
origin.x = 32; <span class="comment">/* 1/2 pixel in 26.6 format */</span>
origin.y = 0;
error = FT_Glyph_To_Bitmap(
&glyph,
<em>render_mode</em>,
&origin,
1 ); <span class="comment">/* destroy original image == true */</span>
</div>
<p>Some notes:</p>
<ul>
<li>
<p>The first parameter is the address of the source glyph's
handle. When the function is called, it reads its to access the
source glyph object. After the call, the handle will point to a
<em>new</em> glyph object that contains the rendered bitmap.</p>
</li>
<li>
<p>The second parameter is a standard render mode, that is used to
specify what kind of bitmap we want. It can be
<tt>FT_RENDER_MODE_DEFAULT</tt> for an 8-bit anti-aliased pixmap,
or <tt>FT_RENDER_MODE_MONO</tt> for a 1-bit monochrome bitmap.</p>
</li>
<li>
<p>The third parameter is a pointer to a two-dimensional vector
that is used to translate the source glyph image before the
conversion. Note that the source image will be translated back to
its original position (and will thus be left unchanged) after the
call. If you do not need to translate the source glyph before
rendering, set this pointer to 0.</p>
</li>
<li>
<p>The last parameter is a boolean that indicates whether the
source glyph object should be destroyed by the function. If
false, the original glyph object is never destroyed, even if its
handle is lost (it is up to client applications to keep it).</p>
</li>
</ul>
<p>The new glyph object always contains a bitmap (if no error is
returned), and you must <em>typecast</em> its handle to the
<tt>FT_BitmapGlyph</tt> type in order to access its content. This
type is a sort of ‘subclass’ of <tt>FT_Glyph</tt> that
contains additional fields (see <a
href="../reference/ft2-glyph_management.html#FT_BitmapGlyphRec">
<tt>FT_BitmapGlyphRec</tt></a>):</p>
<center>
<table width="80%" cellpadding=5>
<tr valign=top>
<td>
<tt>left</tt>
</td>
<td>
<p>Just like the <tt>bitmap_left</tt> field of a glyph slot, this
is the horizontal distance from the glyph origin (0,0) to the
leftmost pixel of the glyph bitmap. It is expressed in integer
pixels.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>top</tt>
</td>
<td>
<p>Just like the <tt>bitmap_top</tt> field of a glyph slot, this
is the vertical distance from the glyph origin (0,0) to the
topmost pixel of the glyph bitmap (more precise, to the pixel just
above the bitmap). This distance is expressed in integer pixels,
and is positive for upwards y.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>bitmap</tt>
</td>
<td>
<p>This is a bitmap descriptor for the glyph object, just like the
<tt>bitmap</tt> field in a glyph slot.</p>
</td>
</tr>
</table>
</center>
<hr>
<h3>
3. Global glyph metrics
</h3>
<p>Unlike glyph metrics, global metrics are used to describe distances
and features of a whole font face. They can be expressed either in 26.6
pixel format or in design ‘font units’ for scalable
formats.</p>
<h4>
a. Design global metrics
</h4>
<p>For scalable formats, all global metrics are expressed in font
units in order to be later scaled to the device space, according to
the rules described in the last chapter of this section of the
tutorial. You can access them directly as simple fields of a
<tt>FT_Face</tt> handle.</p>
<p>However, you need to check that the font face's format is scalable
before using them. One can do it by using the macro
<tt>FT_IS_SCALABLE</tt> which returns true when appropriate.</p>
<p>In this case, you can access the global design metrics as:</p>
<center>
<table width="90%" cellpadding=5>
<tr valign=top>
<td>
<tt>units_per_EM</tt>
</td>
<td>
<p>This is the size of the EM square for the font face. It is
used by scalable formats to scale design coordinates to device
pixels, as described in the last chapter of this section. Its
value usually is 2048 (for TrueType) or 1000 (for Type 1),
but others are possible too. It is set to 1 for fixed-size
formats like FNT/FON/PCF/BDF.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>bbox</tt>
</td>
<td>
<p>The global bounding box is defined as the largest rectangle
that can enclose all the glyphs in a font face.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>ascender</tt>
</td>
<td>
<p>The ascender is the vertical distance from the horizontal
baseline to the highest ‘character’ coordinate in a
font face. Unfortunately, font formats define the ascender
differently. For some, it represents the ascent of all capital
latin characters (without accents), for others it is the ascent of
the highest accented character, and finally, other formats define
it as being equal to <tt>bbox.yMax</tt>.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>descender</tt>
</td>
<td>
<p>The descender is the vertical distance from the horizontal
baseline to the lowest ‘character’ coordinate in a
font face. Unfortunately, font formats define the descender
differently. For some, it represents the descent of all capital
latin characters (without accents), for others it is the ascent of
the lowest accented character, and finally, other formats define
it as being equal to <tt>bbox.yMin</tt>. This field is
negative for values below the baseline.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>height</tt>
</td>
<td>
<p>This field is simply used to compute a <i>default</i> line
spacing (i.e., the baseline-to-baseline distance) when writing
text with this font. Note that it usually is larger than the sum
of the ascender and descender taken as absolute values. There is
also no guarantee that no glyphs extend above or below subsequent
baselines when using this distance.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>max_advance_width</tt>
</td>
<td>
<p>This field gives the maximum horizontal cursor advance for all
glyphs in the font. It can be used to quickly compute the maximum
advance width of a string of text. <em>It doesn't correspond to
the maximum glyph image width!</em></p>
</td>
</tr>
<tr valign=top>
<td>
<tt>max_advance_height</tt>
</td>
<td>
<p>Same as <tt>max_advance_width</tt> but for vertical text
layout.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>underline_position</tt>
</td>
<td>
<p>When displaying or rendering underlined text, this value
corresponds to the vertical position, relative to the baseline, of
the underline bar's center. It is negative if it is below the
baseline.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>underline_thickness</tt>
</td>
<td>
<p>When displaying or rendering underlined text, this value
corresponds to the vertical thickness of the underline.</p>
</td>
</tr>
</table>
</center>
<p>Notice how, unfortunately, the values of the ascender and the
descender are not reliable (due to various discrepancies in font
formats).</p>
<h4>
b. Scaled global metrics
</h4>
<p>Each size object also contains a scaled versions of some of the
global metrics described above. They can be accessed directly through
the <tt>face->size->metrics</tt> structure.</p>
<p>Note that these values correspond to scaled versions of the design
global metrics, <em>with no rounding or grid-fitting performed</em>.
They are also completely independent of any hinting process. In other
words, don't rely on them to get exact metrics at the pixel level.
They are expressed in 26.6 pixel format.</p>
<center>
<table width="80%" cellpadding=5>
<tr valign=top>
<td>
<tt>ascender</tt>
</td>
<td>
<p>The scaled version of the original design ascender.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>descender</tt>
</td>
<td>
<p>The scaled version of the original design descender.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>height</tt>
</td>
<td>
<p>The scaled version of the original design text height (the
vertical distance from one baseline to the next). This is
probably the only field you should really use in this
structure.</p>
<p>Be careful not to confuse it with the ‘height’
field in the <a
href="../reference/ft2-base_interface.html#FT_Glyph_Metrics">
<tt>FT_Glyph_Metrics</tt></a> structure.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>max_advance</tt>
</td>
<td>
<p>The scaled version of the original design max advance.</p>
</td>
</tr>
</table>
</center>
<p>Note that the <tt>face->size->metrics</tt> structure contains
other fields that are used to scale design coordinates to device
space. They are described in the last chapter.</p>
<h4>
c. Kerning
</h4>
<p>Kerning is the process of adjusting the position of two subsequent
glyph images in a string of text in order to improve the general
appearance of text. Basically, it means that when the glyph for an
‘A’ is followed by the glyph for a ‘V’, the
space between them can be slightly reduced to avoid extra
‘diagonal whitespace’.</p>
<p>Note that in theory kerning can happen both in the horizontal and
vertical direction between two glyphs; however, it only happens in the
horizontal direction in nearly all cases except really extreme
ones.</p>
<p>Not all font formats contain kerning information, and not all
kerning formats are supported by FreeType; in particular, for TrueType
fonts, the API can only access kerning via the ‘kern’
table; <b>OpenType kerning via the ‘GPOS’ table is not
supported.</b> You need a higher-level library like <a
href="http://www.pango.org">Pango</a> or <a
href="http://www.icu-project.org">ICU</a> to handle that.</p>
<p>Sometimes, the font file is associated with an additional file that
contains various glyph metrics, including kerning, but no glyph
images. A good example is the Type 1 format where glyph images
are stored in a file with extension <tt>.pfa</tt> or <tt>.pfb</tt>,
and where kerning metrics can be found in a file with extension
<tt>.afm</tt> or <tt>.pfm</tt>.</p>
<p>FreeType 2 allows you to deal with this, by providing the <a
href="../reference/ft2-base_interface.html#FT_Attach_File">
<tt>FT_Attach_File</tt></a> and <a
href="../reference/ft2-base_interface.html#FT_Attach_Stream">
<tt>FT_Attach_Stream</tt></A> APIs. Both functions are used to load
additional metrics into a face object by reading them from an
additional format-specific file. For example, you could open a
Type 1 font by doing the following:</p>
<div class="pre">
error = FT_New_Face( library, "/usr/shared/fonts/cour.pfb",
0, &face );
if ( error ) { ... }
error = FT_Attach_File( face, "/usr/shared/fonts/cour.afm" );
if ( error )
{ ... could not read kerning and additional metrics ... }
</div>
<p>Note that <tt>FT_Attach_Stream</tt> is similar to
<tt>FT_Attach_File</tt> except that it doesn't take a C string to
name the extra file but a <tt>FT_Stream</tt> handle. Also,
<em>reading a metrics file is in no way mandatory</em>.</p>
<p>Finally, the file attachment APIs are very generic and can be used
to load any kind of extra information for a given face. The nature of
the additional content is entirely font format specific.</p>
<p>FreeType 2 allows you to retrieve the kerning information for
two glyphs through the <tt>FT_Get_Kerning</tt> function, whose
interface looks like:</p>
<div class="pre">
FT_Vector kerning;
...
error = FT_Get_Kerning( face, <span class="comment">/* handle to face object */</span>
left, <span class="comment">/* left glyph index */</span>
right, <span class="comment">/* right glyph index */</span>
<em>kerning_mode</em>, <span class="comment">/* kerning mode */</span>
&kerning ); <span class="comment">/* target vector */</span>
</div>
<p>As you see, the function takes a handle to a face object, the
indices of the left and right glyph for which the kerning value is
desired, as well as an integer, called the <em>kerning mode</em>, and
a pointer to a destination vector that receives the corresponding
distances.</p>
<p>The kerning mode is very similar to the <em>bbox mode</em>
described in a previous chapter. It is a enumeration that indicates
how the kerning distances are expressed in the target vector.</p>
<p>The default value is <tt>FT_KERNING_DEFAULT</tt> which has
value 0. It corresponds to kerning distances expressed in 26.6
grid-fitted pixels (which means that the values are multiples of 64).
For scalable formats, this means that the design kerning distance is
scaled, then rounded.</p>
<p>The value <tt>FT_KERNING_UNFITTED</tt> corresponds to kerning
distances expressed in 26.6 unfitted pixels (i.e., that do not
correspond to integer coordinates). It is the design kerning distance
that is scaled without rounding.</p>
<p>Finally, the value <tt>FT_KERNING_UNSCALED</tt> is used to return
the design kerning distance, expressed in font units. You can later
scale it to the device space using the computations explained in the
last chapter of this section.</p>
<p>Note that the ‘left’ and ‘right’ positions
correspond to the <em>visual order</em> of the glyphs in the string of
text. This is important for bidirectional text, or simply when
writing right-to-left text.</p>
<hr>
<h3>
4. Simple text rendering: kerning + centering
</h3>
<p>In order to show off what we just learned, we will now demonstrate
how to modify the example code that was provided in section I to
render a string of text, and enhance it to support kerning and delayed
rendering.</p>
<h4>
a. Kerning support
</h4>
<p>Adding support for kerning to our code is trivial, as long as we
consider that we are still dealing with a left-to-right script like
Latin. We simply need to retrieve the kerning distance between two
glyphs in order to alter the pen position appropriately. The code
looks like:</p>
<div class="pre">
FT_GlyphSlot slot = face->glyph; <span class="comment">/* a small shortcut */</span>
FT_UInt glyph_index;
FT_Bool use_kerning;
FT_UInt previous;
int pen_x, pen_y, n;
... initialize library ...
... create face object ...
... set character size ...
pen_x = 300;
pen_y = 200;
use_kerning = FT_HAS_KERNING( face );
previous = 0;
for ( n = 0; n < num_chars; n++ )
{
<span class="comment">/* convert character code to glyph index */</span>
glyph_index = FT_Get_Char_Index( face, text[n] );
<span class="comment">/* retrieve kerning distance and move pen position */</span>
if ( use_kerning && previous && glyph_index )
{
FT_Vector delta;
FT_Get_Kerning( face, previous, glyph_index,
FT_KERNING_DEFAULT, &delta );
pen_x += delta.x >> 6;
}
<span class="comment">/* load glyph image into the slot (erase previous one) */</span>
error = FT_Load_Glyph( face, glyph_index, FT_LOAD_RENDER );
if ( error )
continue; <span class="comment">/* ignore errors */</span>
<span class="comment">/* now draw to our target surface */</span>
my_draw_bitmap( &slot->bitmap,
pen_x + slot->bitmap_left,
pen_y - slot->bitmap_top );
<span class="comment">/* increment pen position */</span>
pen_x += slot->advance.x >> 6;
<span class="comment">/* record current glyph index */</span>
previous = glyph_index;
}
</div>
<p>We are done. Some notes:</p>
<ul>
<li>
<p>As kerning is determined from glyph indices, we need to
explicitly convert our character codes into glyph indices, then
later call <tt>FT_Load_Glyph</tt> instead of
<tt>FT_Load_Char</tt>.</p>
</li>
<li>
<p>We use a boolean named <tt>use_kerning</tt> which is set with
the result of the macro <tt>FT_HAS_KERNING</tt>. It is certainly
faster not to call <tt>FT_Get_Kerning</tt> when we know that the
font face does not contain kerning information.</p>
</li>
<li>
<p>We move the position of the pen <em>before</em> a new glyph is
drawn.</p>
</li>
<li>
<p>We initialize the variable <tt>previous</tt> with the
value 0, which always corresponds to the ‘missing
glyph’ (also called <tt>.notdef</tt> in the Postscript
world). There is never any kerning distance associated with this
glyph.</p>
</li>
<li>
<p>We do not check the error code returned by
<tt>FT_Get_Kerning</tt>. This is because the function always sets
the content of <tt>delta</tt> to (0,0) when an error occurs.</p>
</li>
</ul>
<h4>
b. Centering
</h4>
<p>Our code begins to become interesting but it is still a bit too
simple for normal use. For example, the position of the pen is
determined before we do the rendering; normally, you would rather
layout the text and measure it before computing its final position
(centering, etc.) or perform things like word-wrapping.</p>
<p>Let us now decompose our text rendering function into two distinct
but successive parts: The first one will position individual glyph
images on the baseline, while the second one will render the glyphs.
As we will see, this has many advantages.</p>
<p>We will thus start by storing individual glyph images, as well as
their position on the baseline. This can be done with code like:</p>
<div class="pre">
FT_GlyphSlot slot = face->glyph; <span class="comment">/* a small shortcut */</span>
FT_UInt glyph_index;
FT_Bool use_kerning;
FT_UInt previous;
int pen_x, pen_y, n;
FT_Glyph glyphs[MAX_GLYPHS]; <span class="comment">/* glyph image */</span>
FT_Vector pos [MAX_GLYPHS]; <span class="comment">/* glyph position */</span>
FT_UInt num_glyphs;
... initialize library ...
... create face object ...
... set character size ...
pen_x = 0; <span class="comment">/* start at (0,0) */</span>
pen_y = 0;
num_glyphs = 0;
use_kerning = FT_HAS_KERNING( face );
previous = 0;
for ( n = 0; n < num_chars; n++ )
{
<span class="comment">/* convert character code to glyph index */</span>
glyph_index = FT_Get_Char_Index( face, text[n] );
<span class="comment">/* retrieve kerning distance and move pen position */</span>
if ( use_kerning && previous && glyph_index )
{
FT_Vector delta;
FT_Get_Kerning( face, previous, glyph_index,
FT_KERNING_DEFAULT, &delta );
pen_x += delta.x >> 6;
}
<span class="comment">/* store current pen position */</span>
pos[num_glyphs].x = pen_x;
pos[num_glyphs].y = pen_y;
<span class="comment">/* load glyph image into the slot without rendering */</span>
error = FT_Load_Glyph( face, glyph_index, FT_LOAD_DEFAULT );
if ( error )
continue; <span class="comment">/* ignore errors, jump to next glyph */</span>
<span class="comment">/* extract glyph image and store it in our table */</span>
error = FT_Get_Glyph( face->glyph, &glyphs[num_glyphs] );
if ( error )
continue; <span class="comment">/* ignore errors, jump to next glyph */</span>
<span class="comment">/* increment pen position */</span>
pen_x += slot->advance.x >> 6;
<span class="comment">/* record current glyph index */</span>
previous = glyph_index;
<span class="comment">/* increment number of glyphs */</span>
num_glyphs++;
}
</div>
<p>This is a very slight variation of our previous code where we
extract each glyph image from the slot, and store it, along with the
corresponding position, in our tables.</p>
<p>Note also that <tt>pen_x</tt> contains the total advance for the
string of text. We can now compute the bounding box of the text
string with a simple function like:</p>
<div class="pre">
void compute_string_bbox( FT_BBox *abbox )
{
FT_BBox bbox;
FT_BBox glyph_bbox;
<span class="comment">/* initialize string bbox to "empty" values */</span>
bbox.xMin = bbox.yMin = 32000;
bbox.xMax = bbox.yMax = -32000;
<span class="comment">/* for each glyph image, compute its bounding box, */</span>
<span class="comment">/* translate it, and grow the string bbox */</span>
for ( n = 0; n < num_glyphs; n++ )
{
FT_Glyph_Get_CBox( glyphs[n], ft_glyph_bbox_pixels,
&glyph_bbox );
glyph_bbox.xMin += pos[n].x;
glyph_bbox.xMax += pos[n].x;
glyph_bbox.yMin += pos[n].y;
glyph_bbox.yMax += pos[n].y;
if ( glyph_bbox.xMin < bbox.xMin )
bbox.xMin = glyph_bbox.xMin;
if ( glyph_bbox.yMin < bbox.yMin )
bbox.yMin = glyph_bbox.yMin;
if ( glyph_bbox.xMax > bbox.xMax )
bbox.xMax = glyph_bbox.xMax;
if ( glyph_bbox.yMax > bbox.yMax )
bbox.yMax = glyph_bbox.yMax;
}
<span class="comment">/* check that we really grew the string bbox */</span>
if ( bbox.xMin > bbox.xMax )
{
bbox.xMin = 0;
bbox.yMin = 0;
bbox.xMax = 0;
bbox.yMax = 0;
}
<span class="comment">/* return string bbox */</span>
*abbox = bbox;
}
</div>
<p>The resulting bounding box dimensions are expressed in integer
pixels and can then be used to compute the final pen position before
rendering the string as in:</p>
<div class="pre">
<span class="comment">/* compute string dimensions in integer pixels */</span>
string_width = string_bbox.xMax - string_bbox.xMin;
string_height = string_bbox.yMax - string_bbox.yMin;
<span class="comment">/* compute start pen position in 26.6 cartesian pixels */</span>
start_x = ( ( my_target_width - string_width ) / 2 ) * 64;
start_y = ( ( my_target_height - string_height ) / 2 ) * 64;
for ( n = 0; n < num_glyphs; n++ )
{
FT_Glyph image;
FT_Vector pen;
image = glyphs[n];
pen.x = start_x + pos[n].x;
pen.y = start_y + pos[n].y;
error = FT_Glyph_To_Bitmap( &image, FT_RENDER_MODE_NORMAL,
&pen, 0 );
if ( !error )
{
FT_BitmapGlyph bit = (FT_BitmapGlyph)image;
my_draw_bitmap( bit->bitmap,
bit->left,
my_target_height - bit->top );
FT_Done_Glyph( image );
}
}
</div>
<p>Some remarks:</p>
<ul>
<li>
<p>The pen position is expressed in the cartesian space (i.e.,
y upwards).</p>
</li>
<li>
<p>We call <tt>FT_Glyph_To_Bitmap</tt> with the <tt>destroy</tt>
parameter set to 0 (false), in order to avoid destroying the
original glyph image. The new glyph bitmap is accessed through
<tt>image</tt> after the call and is typecast to
<tt>FT_BitmapGlyph</tt>.</p>
</li>
<li>
<p>We use translation when calling <tt>FT_Glyph_To_Bitmap</tt>.
This ensures that the <tt>left</tt> and <tt>top</tt> fields of the
bitmap glyph object are already set to the correct pixel
coordinates in the cartesian space.</p>
</li>
<li>
<p>Of course, we still need to convert pixel coordinates from
cartesian to device space before rendering, hence the
<tt>my_target_height - bitmap->top</tt> in the call to
<tt>my_draw_bitmap</tt>.</p>
</li>
</ul>
<p>The same loop can be used to render the string anywhere on our
display surface, without the need to reload our glyph images each
time. We could also decide to implement word wrapping, and only
draw</p>
<hr>
<h3>
5. Advanced text rendering: transformation + centering + kerning
</h3>
<p>We are now going to modify our code in order to be able to easily
transform the rendered string, for example to rotate it. We will start
by performing a few minor improvements:</p>
<h4>
a. packing & translating glyphs
</h4>
<p>We start by packing the information related to a single glyph image
into a single structure instead of parallel arrays. We thus define
the following structure type:</p>
<div class="pre">
typedef struct TGlyph_
{
FT_UInt index; <span class="comment">/* glyph index */</span>
FT_Vector pos; <span class="comment">/* glyph origin on the baseline */</span>
FT_Glyph image; <span class="comment">/* glyph image */</span>
} TGlyph, *PGlyph;
</div>
<p>We also translate each glyph image directly after it is loaded to
its position on the baseline at load time. As we will see, this has
several advantages. Our glyph sequence loader thus becomes:</p>
<div class="pre">
FT_GlyphSlot slot = face->glyph; <span class="comment">/* a small shortcut */</span>
FT_UInt glyph_index;
FT_Bool use_kerning;
FT_UInt previous;
int pen_x, pen_y, n;
TGlyph glyphs[MAX_GLYPHS]; <span class="comment">/* glyphs table */</span>
PGlyph glyph; <span class="comment">/* current glyph in table */</span>
FT_UInt num_glyphs;
... initialize library ...
... create face object ...
... set character size ...
pen_x = 0; <span class="comment">/* start at (0,0) */</span>
pen_y = 0;
num_glyphs = 0;
use_kerning = FT_HAS_KERNING( face );
previous = 0;
glyph = glyphs;
for ( n = 0; n < num_chars; n++ )
{
glyph->index = FT_Get_Char_Index( face, text[n] );
if ( use_kerning && previous && glyph->index )
{
FT_Vector delta;
FT_Get_Kerning( face, previous, glyph->index,
FT_KERNING_MODE_DEFAULT, &delta );
pen_x += delta.x >> 6;
}
<span class="comment">/* store current pen position */</span>
glyph->pos.x = pen_x;
glyph->pos.y = pen_y;
error = FT_Load_Glyph( face, glyph_index, FT_LOAD_DEFAULT );
if ( error ) continue;
error = FT_Get_Glyph( face->glyph, &glyph->image );
if ( error ) continue;
<span class="comment">/* translate the glyph image now */</span>
FT_Glyph_Transform( glyph->image, 0, &glyph->pos );
pen_x += slot->advance.x >> 6;
previous = glyph->index;
<span class="comment">/* increment number of glyphs */</span>
glyph++;
}
<span class="comment">/* count number of glyphs loaded */</span>
num_glyphs = glyph - glyphs;
</div>
<p>Note that translating glyphs now has several advantages. The first
one is that we don't need to translate the glyph bbox when we compute
the string's bounding box. The code becomes:</p>
<div class="pre">
void compute_string_bbox( FT_BBox *abbox )
{
FT_BBox bbox;
bbox.xMin = bbox.yMin = 32000;
bbox.xMax = bbox.yMax = -32000;
for ( n = 0; n < num_glyphs; n++ )
{
FT_BBox glyph_bbox;
FT_Glyph_Get_CBox( glyphs[n], ft_glyph_bbox_pixels,
&glyph_bbox );
if (glyph_bbox.xMin < bbox.xMin)
bbox.xMin = glyph_bbox.xMin;
if (glyph_bbox.yMin < bbox.yMin)
bbox.yMin = glyph_bbox.yMin;
if (glyph_bbox.xMax > bbox.xMax)
bbox.xMax = glyph_bbox.xMax;
if (glyph_bbox.yMax > bbox.yMax)
bbox.yMax = glyph_bbox.yMax;
}
if ( bbox.xMin > bbox.xMax )
{
bbox.xMin = 0;
bbox.yMin = 0;
bbox.xMax = 0;
bbox.yMax = 0;
}
*abbox = bbox;
}
</div>
<p>Now take a closer look: The <tt>compute_string_bbox</tt> function
can now compute the bounding box of a transformed glyph string. For
example, we can do something like:</p>
<div class="pre">
FT_BBox bbox;
FT_Matrix matrix;
FT_Vector delta;
... load glyph sequence ...
... set up "matrix" and "delta" ...
<span class="comment">/* transform glyphs */</span>
for ( n = 0; n < num_glyphs; n++ )
FT_Glyph_Transform( glyphs[n].image, &matrix, &delta );
<span class="comment">/* compute bounding box of transformed glyphs */</span>
compute_string_bbox( &bbox );
</div>
<h4>
b. Rendering a transformed glyph sequence
</h4>
<p>However, directly transforming the glyphs in our sequence is not a
good idea if we want to reuse them in order to draw the text string
with various angles or transformations. It is better to perform the
affine transformation just before the glyph is rendered, as in the
following code:</p>
<div class="pre">
FT_Vector start;
FT_Matrix matrix;
FT_Glyph image;
FT_Vector pen;
FT_BBox bbox;
<span class="comment">/* get bbox of original glyph sequence */</span>
compute_string_bbox( &string_bbox );
<span class="comment">/* compute string dimensions in integer pixels */</span>
string_width = (string_bbox.xMax - string_bbox.xMin) / 64;
string_height = (string_bbox.yMax - string_bbox.yMin) / 64;
<span class="comment">/* set up start position in 26.6 cartesian space */</span>
start.x = ( ( my_target_width - string_width ) / 2 ) * 64;
start.y = ( ( my_target_height - string_height ) / 2 ) * 64;
<span class="comment">/* set up transform (a rotation here) */</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 );
pen = start;
for ( n = 0; n < num_glyphs; n++ )
{
<span class="comment">/* create a copy of the original glyph */</span>
error = FT_Glyph_Copy( glyphs[n].image, &image );
if ( error ) continue;
<span class="comment">/* transform copy (this will also translate it to the */</span>
<span class="comment">/* correct position */</span>
FT_Glyph_Transform( image, &matrix, &pen );
<span class="comment">/* check bounding box; if the transformed glyph image */</span>
<span class="comment">/* is not in our target surface, we can avoid rendering it */</span>
FT_Glyph_Get_CBox( image, ft_glyph_bbox_pixels, &bbox );
if ( bbox.xMax <= 0 || bbox.xMin >= my_target_width ||
bbox.yMax <= 0 || bbox.yMin >= my_target_height )
continue;
<span class="comment">/* convert glyph image to bitmap (destroy the glyph copy!) */</span>
error = FT_Glyph_To_Bitmap(
&image,
FT_RENDER_MODE_NORMAL,
0, <span class="comment">/* no additional translation */</span>
1 ); <span class="comment">/* destroy copy in "image" */</span>
if ( !error )
{
FT_BitmapGlyph bit = (FT_BitmapGlyph)image;
my_draw_bitmap( bit->bitmap,
bit->left,
my_target_height - bit->top );
<span class="comment">/* increment pen position -- */</span>
<span class="comment">/* we don't have access to a slot structure, */</span>
<span class="comment">/* so we have to use advances from glyph structure */</span>
<span class="comment">/* (which are in 16.16 fixed float format) */</span>
pen.x += image.advance.x >> 10;
pen.y += image.advance.y >> 10;
FT_Done_Glyph( image );
}
}
</div>
<p>There are a few changes compared to the original version of this
code:</p>
<ul>
<li>
<p>We keep the original glyph images untouched; instead, we
transform a copy.</p>
</li>
<li>
<p>We perform clipping computations in order to avoid rendering
& drawing glyphs that are not within our target surface</p>
</li>
<li>
<p>We always destroy the copy when calling
<tt>FT_Glyph_To_Bitmap</tt> in order to get rid of the transformed
scalable image. Note that the image is not destroyed if the
function returns an error code (which is why
<tt>FT_Done_Glyph</tt> is only called within the compound
statement.</p>
</li>
<li>
<p>The translation of the glyph sequence to the start pen position
is integrated in the call to <tt>FT_Glyph_Transform</tt> instead
of <tt>FT_Glyph_To_Bitmap</tt>.</p>
</li>
</ul>
<p>It is possible to call this function several times to render the
string width different angles, or even change the way <tt>start</tt>
is computed in order to move it to different place.</p>
<p>This code is the basis of the FreeType 2 demonstration program
named <tt>ftstring.c</tt>. It could be easily extended to perform
advanced text layout or word-wrapping in the first part, without
changing the second one.</p>
<p>Note, however, that a normal implementation would use a glyph cache
in order to reduce memory needs. For example, let us assume that our
text string is ‘FreeType&rsquo'. We would store three identical
glyph images in our table for the letter ‘e’, which isn't
optimal (especially when you consider longer lines of text, or even
whole pages).</p>
<hr>
<h3>
6. Accessing metrics in design font units, and scaling them
</h3>
<p>Scalable font formats usually store a single vectorial image, called
an <em>outline</em>, for each glyph in a face. Each outline is defined
in an abstract grid called the <em>design space</em>, with coordinates
expressed in nominal <em>font units</em>. When a glyph image is loaded,
the font driver usually scales the outline to device space according to
the current character pixel size found in a <tt>FT_Size</tt> object.
The driver may also modify the scaled outline in order to significantly
improve its appearance on a pixel-based surface (a process known as
<em>hinting</em> or <em>grid-fitting</em>).</p>
<p>This chapter describes how design coordinates are scaled to the
device space, and how to read glyph outlines and metrics in font units.
This is important for a number of things:</p>
<ul>
<li>
<p>‘true’ WYSIWYG text layout</p>
</li>
<li>
<p>accessing font content for conversion or analysis purposes</p>
</li>
</ul>
<h4>
a. Scaling distances to device space
</h4>
<p>Design coordinates are scaled to the device space using a simple
scaling transformation whose coefficients are computed with the help
of the <em>character pixel size</em>:</p>
<div class="example">
device_x = design_x * x_scale
device_y = design_y * y_scale
x_scale = pixel_size_x / EM_size
y_scale = pixel_size_y / EM_size
</div>
<p>Here, the value <tt>EM_size</tt> is font-specific and corresponds
to the size of an abstract square of the design space (called the
<em>EM</em>), which is used by font designers to create glyph images.
It is thus expressed in font units. It is also accessible directly
for scalable font formats as <tt>face->units_per_EM</tt>. You
should check that a font face contains scalable glyph images by using
the <tt>FT_IS_SCALABLE</tt> macro, which returns true when
appropriate.</p>
<p>When you call the function <tt>FT_Set_Pixel_Sizes</tt>, you are
specifying the value of <tt>pixel_size_x</tt> and
<tt>pixel_size_y</tt> FreeType shall use. The library will
immediately compute the values of <tt>x_scale</tt> and
<tt>y_scale</tt>.</p>
<p>When you call the function <tt>FT_Set_Char_Size</tt>, you are
specifying the character size in physical <em>points</em>, which is
used, along with the device's resolutions, to compute the character
pixel size and the corresponding scaling factors.</p>
<p>Note that after calling any of these two functions, you can access
the values of the character pixel size and scaling factors as fields
of the <tt>face->size->metrics</tt> structure. These fields
are:</p>
<center>
<table width="80%" cellpadding="5">
<tr valign=top>
<td>
<tt>x_ppem</tt>
</td>
<td>
<p>The field name stands for ‘x pixels per EM’;
this is the horizontal size in integer pixels of the EM square,
which also is the <em>horizontal character pixel size</em>, called
<tt>pixel_size_x</tt> in the above example.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>y_ppem</tt>
</td>
<td>
<p>The field name stands for ‘y pixels per EM’;
this is the vertical size in integer pixels of the EM square,
which also is the <em>vertical character pixel size</em>, called
<tt>pixel_size_y</tt> in the above example.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>x_scale</tt>
</td>
<td>
<p>This is a 16.16 fixed-point scale that is used to directly
scale horizontal distances from design space to 1/64th of device
pixels.</p>
</td>
</tr>
<tr valign=top>
<td>
<tt>y_scale</tt>
</td>
<td>
<p>This is a 16.16 fixed-point scale that is used to directly
scale vertical distances from design space to 1/64th of device
pixels.</p>
</td>
</tr>
</table>
</center>
<p>You can scale a distance expressed in font units to 26.6 pixel
format directly with the help of the <tt>FT_MulFix</tt> function, as
in:</p>
<div class="pre">
<span class="comment">/* convert design distances to 1/64th of pixels */</span>
pixels_x = FT_MulFix( design_x, face->size->metrics.x_scale );
pixels_y = FT_MulFix( design_y, face->size->metrics.y_scale );
</div>
<p>However, you can also scale the value directly with more accuracy
by using doubles:</p>
<div class="pre">
FT_Size_Metrics* metrics = &face->size->metrics; <span class="comment">/* shortcut */</span>
double pixels_x, pixels_y;
double em_size, x_scale, y_scale;
<span class="comment">/* compute floating point scale factors */</span>
em_size = 1.0 * face->units_per_EM;
x_scale = metrics->x_ppem / em_size;
y_scale = metrics->y_ppem / em_size;
<span class="comment">/* convert design distances to floating point pixels */</span>
pixels_x = design_x * x_scale;
pixels_y = design_y * y_scale;
</div>
<h4>
b. Accessing design metrics (glyph & global)
</h4>
<p>You can access glyph metrics in font units simply by specifying the
<tt>FT_LOAD_NO_SCALE</tt> bit flag in <tt>FT_Load_Glyph</tt> or
<tt>FT_Load_Char</tt>. The metrics returned in
<tt>face->glyph->metrics</tt> will all be in font units.</p>
<p>You can access unscaled kerning data using the
<tt>FT_KERNING_MODE_UNSCALED</tt> mode.</p>
<p>Finally, a few global metrics are available directly in font units
as fields of the <tt>FT_Face</tt> handle, as described in
chapter 3 of this section.</p>
<hr>
<h3>
Conclusion
</h3>
<p>This is the end of the second section of the FreeType 2
tutorial. You are now able to access glyph metrics, manage glyph
images, and render text much more intelligently (kerning, measuring,
transforming & caching).</p>
<p>You have now sufficient knowledge to build a pretty decent text
service on top of FreeType 2, and you could possibly stop here if
you want.</p>
<p>The demo programs in the ‘ft2demos’ bundle (especially
‘ftview’) are a kind of reference implementation, and are a
good resource to turn to for answers. They also show how to use
additional features, such as the glyph stroker and cache.</p>
<p>The next section will deal with FreeType 2 internals (like
modules, vector outlines, font drivers, renderers), as well as a few
font format specific issues (mainly, how to access certain TrueType or
Type 1 tables).</p>
</td></tr>
</table>
</center>
<h3 align=center>
<a href="step3.html">FreeType 2 Tutorial Step 3</a>
</h3>
<p><font size=-3>Last update: 10-Apr-2013</font></p>
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