[Freetype-wiki-commit] [A freetype Wiki] Update of "FreeType 2
tutorial/part 1"
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The following page has been changed by WernerLemberg:
http://freetype.freedesktop.org/wiki/FreeType_202_20tutorial_2fpart_201
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#pragma section-numbers on
= Simple glyph loading =
----
[[TableOfContents(3)]]
----
== Introduction ==
This is the first section of the Free''''''Type[[nbsp]]2 tutorial. It
will teach you how to
* initialize the library
* open a font file by creating a new face object
* select a character size in points or in pixels
* load a single glyph image and convert it to a bitmap
* render a very simple string of text
* render a rotated string of text easily
----
== Header files ==
The following are instructions required to compile an application that
uses the Free''''''Type[[nbsp]]2 library. ''Please read them
carefully; we have changed a few things since the last release!''
1. '''Locate the Free''''''Type[[nbsp]]2 `include` directory.'''
You have to add it to your compilation include path. Note that on
Unix systems, you can now run the `freetype-config` script with the
`--cflags` 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.
1. '''Include the file named `ft2build.h`.'''
It contains various macro declarations that are later used to
`#include` the appropriate public Free''''''Type[[nbsp]]2 header
files.
1. '''Include the main Free''''''Type[[nbsp]]2 API header file.'''
You should do that using the macro `FT_FREETYPE_H`, like in the
following example:
{{{#!cplusplus
#include <ft2build.h>
#include FT_FREETYPE_H
}}}
`FT_FREETYPE_H` is a special macro defined in the file `ftheader.h`.
It contains some installation-specific macros to name other public
header files of the Free''''''Type[[nbsp]]2 API.
You can read
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-header_file_macros.html this section of the FreeType 2 API Reference]
for a complete listing of the header macros.
The use of macros in `#include` statements is ANSI-compliant. It is
used for several reasons:
* It avoids some painful conflicts with the
Free''''''Type[[nbsp]]1.x public header files.
* The macro names are not limited to the DOS[[nbsp]]8.3 file naming
limit; names like `FT_MULTIPLE_MASTERS_H` or `FT_SFNT_NAMES_H` are a
lot more readable and explanatory than the real file names `ftmm.h`
and `ftsnames.h`.
* It allows special installation tricks that will not be discussed
here.
'''Note''': Starting with Free''''''Type 2.1.6, the old header file
inclusion scheme is no longer supported. This means that you now get
an error if you do something like the following:
{{{#!cplusplus
#include <freetype/freetype.h>
#include <freetype/ftglyph.h>
...
}}}
----
== Initialize the library ==
Simply create a variable of type
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Library FT_Library]
named, for example, `library`, and call the function
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Init_FreeType FT_Init_FreeType]
as in
{{{#!cplusplus
#include <ft2build.h>
#include FT_FREETYPE_H
FT_Library library;
...
error = FT_Init_FreeType( &library );
if ( error )
{
... an error occurred during library initialization ...
}
}}}
This function is in charge of the following:
* It creates a new instance of the Free''''''Type[[nbsp]]2 library,
and sets the handle `library` to it.
* It loads each module that Free''''''Type knows about in the
library. Among others, your new `library` object is able to handle
True''''''Type, Type[[nbsp]]1, CID-keyed & Open''''''Type/CFF fonts
gracefully.
As you can see, the function returns an error code, like most others
in the Free''''''Type API. An error code of[[nbsp]]0 ''always'' means
that the operation was successful; otherwise, the value describes the
error, and `library` is set to NULL.
----
== Load a font face ==
=== From a font file ===
Create a new `face` object by calling
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_New_Face FT_New_Face].
A ''face'' describes a given typeface and style. For example, ‘Times
New Roman Regular’ and ‘Times New Roman Italic’ correspond to two
different faces.
{{{#!cplusplus
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 simply that it is broken...
}
}}}
As you can certainly imagine, `FT_New_Face` opens a font file, then
tries to extract one face from it. Its parameters are
library:: A handle to the Free''''''Type library instance where the face object is created.
filepathname:: The font file pathname (a standard C string).
face_index:: 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 will be returned if its value is too large. Index[[nbsp]]0 always work, though.
face:: A ''pointer'' to the handle that will be set to describe the new face object. It is set to NULL in case of error.
To know how many faces a given font file contains, simply load its
first face (this is, `face_index` should be set to zero), then check
the value of `face->num_faces` which indicates how many faces are
embedded in the font file.
=== From memory ===
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
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_New_Memory_Face FT_New_Memory_Face]
as in
{{{#!cplusplus
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 ) { ... }
}}}
As you can see, `FT_New_Memory_Face` simply 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 `FT_New_Face`.
=== From other sources (compressed files, network, etc.) ===
There are cases where using a file pathname or preloading the file
into memory is simply not sufficient. With Free''''''Type[[nbsp]]2,
it is possible to provide your own implementation of I/O routines.
This is done through the
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Open_Face FT_Open_Face]
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 Free''''''Type[[nbsp]]2 reference manual in order to
learn how to use it.
----
== Accessing face content ==
A ''face object'' models all information that globally describes the
face. Usually, this data can be accessed directly by dereferencing a
handle, like in `face−>num_glyphs`.
The complete list of available fields in in the
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_FaceRec FT_FaceRec]
structure description. However, we describe here a few of them in
more details:
num_glyphs:: This variable gives the number of ''glyphs'' available in the font face. A glyph is simply a character image. It doesn't necessarily correspond to a ''character code'', though.
flags:: A 32-bit integer containing bit flags used to describe some face properties. For example, the flag `FT_FACE_FLAG_SCALABLE` 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 [http://freetype.freedesktop.org/freetype2/docs/reference/ft2-index.html FreeType 2 API Reference].
units_per_EM:: 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.
num_fixed_sizes:: This field gives the number of embedded bitmap strikes in the current face. A ''strike'' is simply 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!
fixed_sizes:: A pointer to an array of `FT_Bitmap_Size` elements. Each `FT_Bitmap_Size` 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.'''
----
== Setting the current pixel size ==
Free''''''Type[[nbsp]]2 uses ''size objects'' 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[[nbsp]]points.
When the `FT_New_Face` function is called (or one of its cousins), it
''automatically'' creates a new size object for the returned face.
This size object is directly accessible as `face−>size`.
'''''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 simplify the API for the
most common use (i.e., one size per face) while keeping this feature
available through additional functions.''
When a new face object is created, its size object defaults to the
character size of 10[[nbsp]]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.
To do that, simply call
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Set_Char_Size FT_Set_Char_Size].
Here is an example where the character size is set to 16pt for a
300×300[[nbsp]]dpi device:
{{{#!cplusplus
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 */
}}}
Some notes:
* 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.
* The horizontal and vertical device resolutions are expressed in
''dots-per-inch'', or ''dpi''. Normal 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.
* A value of[[nbsp]]0 for the character width means ‘same as
character height’, a value of[[nbsp]]0 for the character height
means ‘same as character width’. Otherwise, it is possible to
specify different character widths and heights.
* Using a value of[[nbsp]]0 for the horizontal or vertical
resolution means 72[[nbsp]]dpi, which is the default.
* The first argument is a handle to a face object, not a size
object.
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
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Set_Pixel_Sizes FT_Set_Pixel_Sizes],
as in
{{{#!cplusplus
error = FT_Set_Pixel_Sizes(
face, /* handle to face object */
0, /* pixel_width */
16 ); /* pixel_height */
}}}
This example will set the character pixel sizes to 16×16 pixels. As
previously, a value of[[nbsp]]0 for one of the dimensions means ‘same
as the other’.
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
`face->fixed_sizes` array.
----
== Loading a glyph image ==
=== Converting a character code into a glyph index ===
Usually, 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 point 65 represents
character ‘A’ in ASCII encoding.
A face object contains one or more tables, called ''charmaps'', that
are used to convert character codes to glyph indices. For example,
most True''''''Type 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). 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, it selects a Unicode
charmap. Free''''''Type tries to emulate 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, including symbol fonts and (older)
fonts for Asian scripts, no Unicode emulation is possible at all.
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 a call to `FT_New_Face`. To convert
a Unicode character code to a font glyph index, we use
`FT_Get_Char_Index`, as in
{{{#!cplusplus
glyph_index = FT_Get_Char_Index( face, charcode );
}}}
This will look up the glyph index corresponding to the given
`charcode` in the charmap that is currently selected for the face. If
no charmap was selected, the function simply returns the charcode.
Note that this is one of the rare Free''''''Type functions that do not
return an error code. However, when a given character code has no
glyph image in the face, the 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.
=== Loading a glyph from the face ===
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 True''''''Type or Type[[nbsp]]1 use vectorial
shapes, named ''outlines'' to describe each glyph. Some formats may
have even more exotic ways of representing glyphs (e.g.,
Meta''''''Font — but this format is not supported). Fortunately,
Free''''''Type[[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 simply 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 `face->glyph`. Its fields are explained by
the
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_GlyphSlotRec FT_GlyphSlotRec]
structure documentation.
Loading a glyph image into the slot is performed by calling
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Load_Glyph FT_Load_Glyph]
as in
{{{#!cplusplus
error = FT_Load_Glyph(
face, /* handle to face object */
glyph_index, /* glyph index */
load_flags ); /* load flags, see below */
}}}
The `load_flags` value is a set of bit flags used to indicate some
special operations. The default value `FT_LOAD_DEFAULT` is[[nbsp]]0.
This function will try to load the corresponding glyph image from the
face:
* 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 `FT_LOAD_NO_BITMAP` flag.
* 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 True''''''Type and Type[[nbsp]]1.
The field `face−>glyph−>format` describes the format used to store the
glyph image in the slot. If it is not `FT_GLYPH_FORMAT_BITMAP`, one
can immediately convert it to a bitmap through
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Render_Glyph FT_Render_Glyph]
as in:
{{{#!cplusplus
error = FT_Render_Glyph( face->glyph, /* glyph slot */
render_mode ); /* render mode */
}}}
The parameter `render_mode` is a set of bit flags used to specify how
to render the glyph image. Set it to `FT_RENDER_MODE_NORMAL` to
render a high-quality anti-aliased (256 gray levels) bitmap, as this
is the default. You can alternatively use `FT_RENDER_MODE_MONO` if
you want to generate a 1-bit monochrome bitmap.
Once you have a bitmapped glyph image, you can access it directly
through `glyph->bitmap` (a simple bitmap descriptor), and position it
through `glyph->bitmap_left` and `glyph->bitmap_top`.
Note that `bitmap_left` is the horizontal distance from the current
pen position to the leftmost border of the glyph bitmap, while
`bitmap_top` 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''.
The next section will give more details on the contents of a glyph
slot and how to access specific glyph information (including metrics).
=== Using other charmaps ===
As said before, when a new face object is created, it will look for a
Unicode charmap and select it. The currently selected charmap is
accessed via `face->charmap`. This field is NULL when no charmap is
selected, which typically happens when you create a new `FT_Face`
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
Free''''''Type[[nbsp]]2. The easiest is when the encoding you need
already has a corresponding enumeration defined in `FT_FREETYPE_H`,
for example `FT_ENCODING_BIG5`. In this case, you can simply call
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Select_CharMap FT_Select_CharMap]
as in:
{{{#!cplusplus
error = FT_Select_CharMap(
face, /* target face object */
FT_ENCODING_BIG5 ); /* encoding */
}}}
Another way is to manually parse the list of charmaps for the face;
this is accessible through the fields `num_charmaps` and `charmaps`
(notice the ‘s’) 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 used to describe it more
precisely. Mainly, one will look at `charmap->platform_id` and
`charmap->encoding_id` that define a pair of values that can be used
to 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
True''''''Type specification but you can also use the file
`FT_TRUETYPE_IDS_H` which defines several helpful constants to deal
with them.
To select a specific encoding, you need to find a corresponding value
pair in the specification, then look for it in the charmaps list.
Don't forget that there are encodings which correspond to several
value pairs due to historical reasons. Here some code to do it:
{{{#!cplusplus
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 ) { ... }
}}}
Once a charmap has been selected, either through `FT_Select_CharMap`
or `FT_Set_CharMap`, it is used by all subsequent calls to
`FT_Get_Char_Index`.
=== Glyph transformations ===
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.
To do that, simply call
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-base_interface.html#FT_Set_Transform FT_Set_Transform], as in:
{{{#!cplusplus
error = FT_Set_Transform(
face, /* target face object */
&matrix, /* pointer to 2x2 matrix */
&delta ); /* pointer to 2d vector */
}}}
This function will set the current transform for a given face object.
Its second parameter is a pointer to a simple
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-basic_types.html#FT_Matrix FT_Matrix]
structure that describes a 2×2 affine matrix. The third parameter is
a pointer to a
[http://freetype.freedesktop.org/freetype2/docs/reference/ft2-basic_types.html#FT_Vector FT_Vector]
structure that describes a simple two-dimensional vector that is used
to translate the glyph image ''after'' the 2×2 transformation.
Note that the matrix pointer can be set to NULL, in which case the
identity transform will be used. Coefficients of the matrix are
otherwise in 16.16 fixed float units.
The vector pointer can also be set to NULL (in which case a delta of
(0,0) will be used). The vector coordinates are expressed in 1/64th
of a pixel (also known as 26.6 fixed floats).
'''''Note''': The transformation is applied to every glyph that is
loaded through `FT_Load_Glyph` 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 at 12[[nbsp]]pixels scaled by[[nbsp]]2 through a transform,
because the hints will have been computed differently (except 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
`FT_Set_Transform`. This is explained in details in a later section
of this tutorial.
Note also that loading a glyph bitmap with a non-identity
transformation produces an error.
----
== Simple text rendering ==
We 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.
The idea is to create a loop that loads one glyph image on each
iteration, converts it to an anti-aliased bitmap, draws it on the
target surface, then increments the current pen position.
=== Basic code ===
The following code performs our simple text rendering with the
functions previously described.
{{{#!cplusplus
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 */
}
}}}
This code needs a few explanations:
* We define a handle named `slot` that points to the face object's
glyph slot. (The type `FT_GlyphSlot` is a pointer.) That is a
convenience to avoid using `face->glyph->XXX` every time.
* We increment the pen position with the vector `slot->advance`,
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.
* The function `my_draw_bitmap` is not part of Free''''''Type but
must be provided by the application to draw the bitmap to the target
surface. In this example, it takes a pointer to an `FT_Bitmap`
descriptor and the position of its top-left corner as arguments.
* The value of `slot->bitmap_top` is positive for an ''upwards''
vertical distance. Assuming that the coordinates taken by
`my_draw_bitmap` use the opposite convention (increasing[[nbsp]]Y
corresponds to downwards scanlines), we substract it from `pen_y`,
instead of adding to it.
=== Refined code ===
The following code is a refined version of the example above. It uses
features and functions of Free''''''Type[[nbsp]]2 that have not yet
been introduced, and which are explained below:
{{{#!cplusplus
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;
}
}}}
We have reduced the size of our code, but it does exactly the same thing:
* We use the function `FT_Load_Char` instead of `FT_Load_Glyph`. As
you probably imagine, it is equivalent to calling
`FT_Get_Char_Index` then `FT_Get_Load_Glyph`.
* We do not use `FT_LOAD_DEFAULT` for the loading mode, but the bit
flag `FT_LOAD_RENDER`. It indicates that the glyph image must be
immediately converted to an anti-aliased bitmap. This is of course
a shortcut that avoids calling `FT_Render_Glyph` explicitly but is
strictly equivalent.
Note that you can also specify that you want a monochrome bitmap
instead by using the addition `FT_LOAD_MONOCHROME` load flag.
=== More advanced rendering ===
Let us try to render transformed text now (for example through a
rotation). We can do this using `FT_Set_Transform`. Here is how to
do it:
{{{#!cplusplus
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->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 < 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;
}
}}}
Some remarks:
* We now use a vector of type `FT_Vector` to store the pen position,
with coordinates expressed as 1/64th of pixels, hence a
multiplication. The position is expressed in cartesian space.
* Glyph images are always loaded, transformed, and described in the
cartesian coordinate system in Free''''''Type (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.
* We set the transformation on each glyph to indicate the rotation
matrix as well as a delta that will move the transformed image to
the current pen position (in cartesian space, not bitmap space).
As a consequence, the values of `bitmap_left` and `bitmap_top`
correspond to the bitmap origin in target space pixels. We thus
don't add `pen.x` or `pen.y` to their values when calling
`my_draw_bitmap`.
* 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.
A complete source code example can be found
[http://freetype.freedesktop.org/freetype2/docs/tutorial/example1.c here].
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 transform is the identity. Hence it can be used as a replacement
(but a more powerful one).
It has however a few shortcomings that we will explain, and solve, in
the next part of this tutorial.
----
== Conclusion ==
In this first section, you have learned the basics of
Free''''''Type[[nbsp]]2, as well as sufficient knowledge how to render
rotated text.
The next section will dive into more details of the API in order to
let you access glyph metrics and images directly, as well as how to
deal with scaling, hinting, kerning, etc.
The third section will discuss issues like modules, caching and a few
other advanced topics like how to use multiple size objects with a
single face. [This part hasn't been written yet.]
["../part 2"]
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