- Glyph Designer 2 1 – Bitmap Font Generator Free Download
- Glyph Designer 2 1 – Bitmap Font Generator Free Version
- Glyph Designer 2 1 – Bitmap Font Generator Free Downloads
- Glyph Designer 2 1 – Bitmap Font Generator Free Printable
A bitmap font is an image/texture file (just like a sprite sheet), and a text file with the glyphs coordinates. For each glyph, you will find its size and position on the texture file, and different parameters for the text positions when you write a sentence (the kernings for example). For most fonts there are 2 files (except fonts in ttf format): cg16b.dds (or tga): containig image with a matrix of glyphs (characters) cg16b.fnt: containing information about position and corrections of each glyph; For the purpose of this guide I'll use cg16b. Luckily you won't to mess with the second one. It will be automatically generated. A UK based indie company making innovative Mac apps and renowned for it's #1 particle design and bitmap font editing tools. Forum; Licenses; We are 71Squared A UK based indie company making innovative Mac apps. Deep Dream Generator App for Mac. Bitmap font generator for Mac. Particle Designer. GlyphTypeFace: Specifies a physical font face that corresponds to a font file on the disk., useful to parse a.TTF file and build glyphs from it. GlyphRun: Represents a sequence of glyphs from a single face of a single font at a single size, and with a single rendering style, with many usefull properties and methods (for example, you can build.
Posted: 17 Mar 2015 at 00:08 by CodeheadOne of the big problems OpenGL runs into after you've got your first few polygons flying around the screen is the lack of a standard method for generating text within the API.
A few techniques have evolved to tackle the problem:
Pre-generated string textures
The simplest and fastest method, a texture is pre-built for each piece of text that needs to be displayed. This is quick to render at run time, but isn't very flexible or efficient.
Polygon glyphs created from outline font definitions
This method produces high quality, scalable text, but this is also the slowest approach due to the overhead of generating and rendering the glyph polygons. Fl studio 10 demo mac.
WGL and GLUT extensions
These extensions do a great job of text rendering. However, these libraries are not universally available on all systems and I have a bad habit of trying to be portable and platform independent.
Bitmapped fonts
Bitmap fonts are fast, flexible and platform independent. However, there are some limitations: Quality suffers when scaling up the texture and the number of possible characters in a font bitmap is limited. Extended or Unicode character sets with accents or non-latin symbols are not well supported.
A bitmapped font is simply an atlas texture containing a collection of glyphs and symbols. (Note: the purple lines are a visual aid, they do not appear on the actual texture.)
The grid layout means that the calculation required to select any given character is quick and simple.
The area containing the selected characters can then be mapped onto a series of polygons to create dynamic strings of text.
Adding width information to the glyphs allows the textured quads to be overlapped to create better looking text with variable character widths.
There are quite a few bitmap font generators around, but I couldn't find one that provided all the features I wanted. So I wrote my own.
Raging bull game. Codehead's Bitmap Font Generator (CBFG) is now at version 1.45 and supports the following features:
- DIB rendering of font gives best font output, regardless of users screen settings
- Global or per character position and width adjustment
- Texture Sizes from 16×16 up to 4096×4096
- Zoom up to 400% for accurate tweaking of character positions
- Anti-aliasing or ClearType (XP+) for smoother looking fonts
- Control of font width
- Font preview option
- TGA export option
- BMP output option
- BFF output in 8, 24 and 32bit colour depths
- C++ example source code for loading and rendering BFF files
- Binary font data export
- Font info dump option
- User configurable colours and startup parameters
Many people have made useful suggestions that have been implemented in CBFG, and the tool has been used on the following projects:
- Floating Sandbox A 2D Physics Simulator developed by Gabriele Giuseppini.
- Beginning Android Games An APress book by Robert Green and Mario Zechner
- SkaPong by Einar
- SF2DBmpFont a font loader for 3DS homebrew by Flarn2006
- ByVac's [BV4629] Touchscreen LCD
Downloads
CBFG Packages
Windows Installer Package
Files only zip
Source Code
CBFG has been open sourced under the BSD licence. You can get v1.45 on GitHub
BFF Loading Code
C/C++ - included in zip/installer.
Glyph Designer 2 1 – Bitmap Font Generator Free Download
Android by Codehead
O'Caml by Einar (local mirror)
SF2DBmpFont a font loader for SF2DLib by Flarn2006
The Future
CBFG hasn't been in active development for a few years now, but there are still a few features I always wanted to add:
ToDo List
- State save option
- Merge/Extract font image
Wish List
- Export in other font generator formats
- Edit font image
- Unicode support
Known Issues
Cleartype system setting can override antialias settings in application.
Please enable JavaScript to view the comments powered by Disqus.II. Managing Glyphs
1. Glyph Metrics
Glyph metrics are, as the name suggests, certain distances associated with each glyph that describe how to position this glyph while creating a text layout.
There are usually two sets of metrics for a single glyph: Those used to represent glyphs in horizontal text layouts (Latin, Cyrillic, Arabic, Hebrew, etc.), and those used to represent glyphs in vertical text layouts (Chinese, Japanese, Korean, Mongolian, etc.).
Note that only a few font formats provide vertical metrics. You can test whether a given face object contains them by using the macro FT_HAS_VERTICAL
, which returns true if appropriate.
Individual glyph metrics can be accessed by first loading the glyph in a face's glyph slot, then accessing them through the face->glyph->metrics
structure, whose type is FT_Glyph_Metrics
. We will discuss this in more detail below; for now, we only note that it contains the following fields.
- width
- This is the width of the glyph image's bounding box. It is independent of the layout direction.
- height
- 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
FT_Size_Metrics
structure. - horiBearingX
- For horizontal text layouts, this is the horizontal distance from the current cursor position to the leftmost border of the glyph image's bounding box.
- horiBearingY
- For horizontal text layouts, this is the vertical distance from the current cursor position (on the baseline) to the topmost border of the glyph image's bounding box.
- horiAdvance
- For horizontal text layouts, this is the horizontal distance to increment the pen position when the glyph is drawn as part of a string of text.
- vertBearingX
- For vertical text layouts, this is the horizontal distance from the current cursor position to the leftmost border of the glyph image's bounding box.
- vertBearingY
- For vertical text layouts, this is the vertical distance from the current cursor position (on the baseline) to the topmost border of the glyph image's bounding box.
- vertAdvance
- For vertical text layouts, this is the vertical distance used to increment the pen position when the glyph is drawn as part of a string of text.
As not all fonts do contain vertical metrics, the values of vertBearingX
, vertBearingY
and vertAdvance
should not be considered reliable if FT_HAS_VERTICAL
returns false.
The following graphics illustrate the metrics more clearly. In case a distance is directed, it is marked with a single arrow, indicating a positive value. The first image displays horizontal metrics, where the baseline is the horizontal axis.
For vertical text layouts, the baseline is vertical, identical to the vertical axis. Contrary to all other arrows, bearingX
shows a negative value in this image.
The metrics found in face->glyph->metrics
are normally expressed in 26.6 pixel format (i.e., 1/64th of pixels), unless you use the FT_LOAD_NO_SCALE
flag when calling FT_Load_Glyph
or FT_Load_Char
. In this case, the metrics are expressed in original font units.
The glyph slot object has also a few other interesting fields that eases a developer's work. You can access them through face->glyph->xxx
, where xxx
is one of the following fields.
- advance
- This field is a
FT_Vector
that holds the transformed advance for the glyph. That is useful when you are using a transformation throughFT_Set_Transform
, as shown in the rotated text example of part I. Other than that, its value is by default (metrics.horiAdvance,0), unless you specifyFT_LOAD_VERTICAL
when loading the glyph image; it is then (0,metrics.vertAdvance). - linearHoriAdvance
- This field contains the linearly scaled value of the glyph's horizontal advance width. Indeed, the value of
metrics.horiAdvance
that is returned in the glyph slot is normally rounded to integer pixel coordinates (i.e., being a multiple of 64) by the font driver that actually loads the glyph image.linearHoriAdvance
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. - linearVertAdvance
- This is the similar to
linearHoriAdvance
but for the glyph's vertical advance height. Its value is only reliable if the font face contains vertical metrics.
2. Managing Glyph Images
The glyph image that is loaded in a glyph slot can be converted into a bitmap, either by using FT_LOAD_RENDER
when loading it, or by calling FT_Render_Glyph
. Each time you load a new glyph image, the previous one is erased from the glyph slot.
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.
The FreeType 2 API has a specific extension that is capable of dealing with glyph images in a flexible and generic way. To use it, you first need to include the FT_GLYPH_H
header file.
a.Extracting the Glyph Image
You can extract a single glyph image very easily. Here some code that shows how to do it.
The following steps are performed. Mac dvd converter pro.
- Create a variable named
glyph
, of typeFT_Glyph
. This is a handle (pointer) to an individual glyph image. - Load the glyph image in the normal way into the face's glyph slot. We don't use
FT_LOAD_RENDER
because we want to grab a scalable glyph image that we can transform later on. - Copy the glyph image from the slot into a new
FT_Glyph
object by callingFT_Get_Glyph
. This function returns an error code and setsglyph
.
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 is really a scalable vector outline. You can access the field glyph->format
if you want to know exactly how the glyph is modeled and stored.
A new glyph object can be destroyed with a call to FT_Done_Glyph
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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 glyph->advance
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 FT_Done_FreeType
doing all the clean-up.
b. Transforming & Copying the Glyph Image
If the glyph image is scalable (i.e., if glyph->format
is not equal to FT_GLYPH_FORMAT_BITMAP
), it is possible to transform the image anytime by a call to FT_Glyph_Transform
.
You can also copy a single glyph image with FT_Glyph_Copy
.
Note that the 2×2 transformation matrix is always applied to the 16.16 advance vector in the glyph; you thus don't need to recompute it.
c. Measuring the Glyph Image
You can also retrieve the control (bounding) box of any glyph image (scalable or not) through the FT_Glyph_Get_CBox
function.
Coordinates are relative to the glyph origin (0,0), using the y upwards convention. This function takes a special argument, the bbox mode, to indicate how box coordinates are expressed.
If the glyph has been loaded with FT_LOAD_NO_SCALE
, bbox_mode
must be set to FT_GLYPH_BBOX_UNSCALED
to get unscaled font units in 26.6 pixel format. The value FT_GLYPH_BBOX_SUBPIXELS
is another name for this constant.
Note that the box's maximum coordinates are exclusive, which means that you can always compute the width and height of the glyph image (regardless of using integer or 26.6 coordinates) with a simple subtraction.
Note also that for 26.6 coordinates, if FT_GLYPH_BBOX_GRIDFIT
is used as the bbox mode, the coordinates are also grid-fitted, which corresponds to the following four lines of pseudo-code.
To get the bbox in integer pixel coordinates, set bbox_mode
to FT_GLYPH_BBOX_TRUNCATE
.
Finally, to get the bounding box in grid-fitted pixel coordinates, set bbox_mode
to FT_GLYPH_BBOX_PIXELS
.
[Computing exact bounding boxes can be done with function FT_Outline_Get_BBox
, at the cost of slower execution. You probably don't need it with the possible exception of rotated glyphs.] Commander 3 1 – advanced two pane file manager description.
d. Converting the Glyph Image to a Bitmap
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 FT_Glyph_To_Bitmap
function, which handles any glyph object.
Some notes.
- The first parameter is the address of the source glyph's handle. When the function is called, it reads it to access the source glyph object. After the call, the handle points to a new glyph object that contains the rendered bitmap.
- The second parameter is a standard render mode to specify what kind of bitmap we want. For example, it can be
FT_RENDER_MODE_DEFAULT
for an 8-bit anti-aliased pixmap, orFT_RENDER_MODE_MONO
for a 1-bit monochrome bitmap. - The third parameter is a pointer to a two-dimensional vector to translate the source glyph image before the conversion. After the call, the source image is translated back to its original position (and is thus left unchanged). If you do not need to translate the source glyph before rendering, set this pointer to NULL.
- 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).
The new glyph object always contains a bitmap (if no error is returned), and you must typecast its handle to the FT_BitmapGlyph
type in order to access its content. This type is a sort of ‘subclass' of FT_Glyph
that contains additional fields (see FT_BitmapGlyphRec
).
- left
- Just like the
bitmap_left
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. - top
- Just like the
bitmap_top
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. - bitmap
- This is a bitmap descriptor for the glyph object, just like the
bitmap
field in a glyph slot.
3. Global Glyph Metrics
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 (unscaled) font units for scalable formats.
a. Design global metrics
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 section of this tutorial part. You can access them directly as fields of an FT_Face
handle.
However, you need to check that the font face's format is scalable before using them. One can do it with macro FT_IS_SCALABLE
, which returns true when appropriate.
Here a table of the global design metrics for scalable faces.
- units_per_EM
- 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 section of this tutorial part. Its value usually is 2048 (for TrueType) or 1000 (for Type 1 or CFF), but other values are possible, too. It is set to 1 for fixed-size formats like FNT, FON, PCF, or BDF.
- bbox
- The global bounding box is defined as the smallest rectangle that can enclose all the glyphs in a font face.
- ascender
- The ascender is the vertical distance from the horizontal baseline to the highest ‘character' coordinate in a font face. Unfortunately, font formats don't define the ascender in a uniform way. For some formats, 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
bbox.yMax
. - descender
- The descender is the vertical distance from the horizontal baseline to the lowest ‘character' coordinate in a font face. Unfortunately, font formats don't define the descender in a uniform way. For some formats, 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
bbox.yMin
. This field is negative for values below the baseline. - height
- This field represents a default 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 – think of it as a value the designer of the font finds appropriate.
- max_advance_width
- 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. It doesn't correspond to the maximum glyph image width!
- max_advance_height
- Same as
max_advance_width
but for vertical text layout. - underline_position
- 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.
- underline_thickness
- When displaying or rendering underlined text, this value corresponds to the vertical thickness of the underline.
Notice that the values of the ascender and the descender are not reliable (due to various discrepancies in font formats), unfortunately.
b. Scaled Global Metrics
Each size object also contains a scaled version of some of the global metrics described above, to be directly accessed through the face->size->metrics
structure (of type FT_Size_Metrics
). No grid-fitting is performed for those values. 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 but rounded for historical reasons.
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. It is rounded to an integer value.
Be careful not to confuse it with the ‘height' field in the FT_Glyph_Metrics
structure.
Note that the face->size->metrics
structure contains other fields that are used to scale design coordinates to device space. They are described in the last section.
c. Kerning
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. For example, if a glyph for an uppercase ‘A' is followed by a glyph for an uppercase ‘V', the space between the two glyphs can be slightly reduced to avoid extra ‘diagonal whitespace'.
Note that in theory kerning can happen both in the horizontal and vertical direction between two glyphs; however, it only happens in a single direction in nearly all cases.
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. OpenType kerning via the ‘GPOS' table is not supported! You need a higher-level library like HarfBuzz, Pango, or ICU, since GPOS kerning requires contextual string handling.
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 files with extension .pfa
or .pfb
, while kerning metrics can be found in files with extension .afm
or .pfm
.
FreeType 2 allows you to deal with this, by providing the FT_Attach_File
and FT_Attach_Stream
APIs. Both functions are used to load additional metrics into a face object by reading them from an additional format-specific file. Here an example, opening a Type 1 font.
Note that FT_Attach_Stream
is similar to FT_Attach_File
except that it doesn't take a C string to name the extra file but an FT_Stream
handle. Also, reading a metrics file is in no way mandatory.
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.
FreeType 2 allows you to retrieve the kerning information between two glyphs through the FT_Get_Kerning
function.
This function takes a handle to a face object, the indices of the left and right glyph for which the kerning value is desired, an integer, called the kerning mode, and a pointer to a destination vector that receives the corresponding distances.
The kerning mode is very similar to the bbox mode described in a previous section. It is a enumeration that indicates how the kerning distances are expressed in the target vector.
The default value is FT_KERNING_DEFAULT
, 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.
The value FT_KERNING_UNFITTED
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.
Finally, the value FT_KERNING_UNSCALED
indicates 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 section of this part.
Note that the ‘left' and ‘right' positions correspond to the visual order of the glyphs in the string of text. This is important for bidirectional or right-to-left text.
4. Simple Text Rendering: Kerning and Centering
In order to show off what we have just learned, we now demonstrate how to modify the example code that was provided in part I to render a string of text, and enhance it to support kerning and delayed rendering.
a. Kerning Support
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.
We are done. Some notes.
- As kerning is determined by glyph indices, we need to explicitly convert our character codes into glyph indices, then later call
FT_Load_Glyph
instead ofFT_Load_Char
. - We use a boolean named
use_kerning
, which is set to the result of the macroFT_HAS_KERNING
. It is certainly faster not to callFT_Get_Kerning
when we know that the font face does not contain kerning information. - We move the position of the pen before a new glyph is drawn.
- We initialize the variable
previous
with the value 0, which always corresponds to the ‘missing glyph' (also called.notdef
in the PostScript world). There is never any kerning distance associated with this glyph. - We do not check the error code returned by
FT_Get_Kerning
. This is because the function always sets the content ofdelta
to (0,0) if an error occurs.
b. Centering
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 determine the layout of the text and measure it before computing its final position (centering, etc.), or perform things like word-wrapping.
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Let us now decompose our text rendering function into two distinct but successive parts: The first one positions individual glyph images on the baseline, while the second one renders the glyphs. As we will see, this has many advantages.
We thus start by storing individual glyph images, as well as their position on the baseline.
This is a very slight variation of our previous code; we extract each glyph image from the slot, then store it, along with the corresponding position, in our tables.
Note also that pen_x
contains the total advance for the string of text. We can now compute the bounding box of the text string with a simple function.
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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.
In general, the above function does not compute an exact bounding box of a string! As soon as hinting is involved, glyph dimensions must be derived from the resulting outlines. For anti-aliased pixmaps, FT_Outline_Get_BBox
then yields proper results. In case you need 1-bit monochrome bitmaps, it is even necessary to actually render the glyphs because the rules for the conversion from outline to bitmap can also be controlled by hinting instructions (cf. dropout control).
Some remarks.
- The pen position is expressed in the Cartesian space (i.e., y upwards).
- We call
FT_Glyph_To_Bitmap
with thedestroy
parameter set to 0 (false), in order to avoid destroying the original glyph image. The new glyph bitmap is accessed throughimage
after the call and is typecast toFT_BitmapGlyph
. - We use translation when calling
FT_Glyph_To_Bitmap
. This ensures that theleft
andtop
fields of the bitmap glyph object are already set to the correct pixel coordinates in the Cartesian space. - Of course, we still need to convert pixel coordinates from Cartesian to device space before rendering, hence the
my_target_height - bitmap->top
in the call tomy_draw_bitmap
.
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.
5. Advanced Text Rendering: Transformation and Centering and Kerning
We are now going to modify our code in order to be able to easily transform the rendered string, for example, to rotate it. First, some minor improvements.
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a. Packing and Translating Glyphs
We start by packing the information related to a single glyph image into a single structure instead of parallel arrays.
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. Here is our new glyph sequence loader.
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.
With the above modifications, the compute_string_bbox
function can now compute the bounding box of a transformed glyph string, which allows further code simplications.
b. Rendering a Transformed Glyph Sequence
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.
There are a few changes compared to the original version of this code.
- We keep the original glyph images untouched; instead, we transform a copy.
- We perform clipping computations in order to avoid rendering and drawing glyphs that are not within our target surface.
- We always destroy the copy when calling
FT_Glyph_To_Bitmap
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 whyFT_Done_Glyph
is only called within the compound statement). - The translation of the glyph sequence to the start pen position is integrated into the call to
FT_Glyph_Transform
instead ofFT_Glyph_To_Bitmap
.
It is possible to call this function several times to render the string with different angles, or even change the way start
is computed in order to move it to different place.
This code is the basis of the FreeType 2 demonstration program named ftstring.c
. It could be easily extended to perform advanced text layout or word-wrapping in the first part, without changing the second one.
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'. 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).
A FreeType demo program that shows how glyph caching can be implemented is ftview.c
. In general, ‘ftview' is the main program used by the FreeType developer team to check the validity of loading, parsing, and rendering fonts.
Another very useful demo program is ftdiff.c
, demonstrating the use and the optical results of the various rendering and hinting modes provided by FreeType. In particular, it also demonstrates how to do sub-pixel positioning (for unhinted glyphs and ‘light' hinting mode) – all code in this tutorial assumes integer coordinates.
6. Accessing Metrics in Design Font Units, and Scaling Them
Scalable font formats usually store a single vectorial image, called an outline, for each glyph in a face. Each outline is defined in an abstract grid called the design space, with coordinates expressed in font units. 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 an FT_Size
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 hinting or grid-fitting).
This section 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.
- ‘True' WYSIWYG text layout.
- Accessing font content for conversion or analysis purposes.
a. Scaling Distances to Device Space
Design coordinates are scaled to the device space using a simple scaling transformation whose coefficients are computed with the help of the character pixel size.
Here, the value EM_size
is font-specific and corresponds to the size of an abstract square of the design space (called the 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 face->units_per_EM
. You should check that a font face contains scalable glyph images by using the FT_IS_SCALABLE
macro, which returns true if appropriate.
When you call the function FT_Set_Pixel_Sizes
, you are specifying integer values of pixel_size_x
and pixel_size_y
FreeType shall use. The library will immediately compute the values of x_scale
and y_scale
.
When you call the function FT_Set_Char_Size
, you are specifying the character size in physical points, which is used, along with the device's resolutions, to compute the character pixel size and the corresponding scaling factors. Here, the scaling factors can correspond to fractional ppem values.
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 face->size->metrics
structure.
- x_ppem
- The field name stands for ‘x pixels per EM'; this is the horizontal size rounded to integer pixels of the EM square, which also is the horizontal character pixel size, called
pixel_size_x
in the above example. - y_ppem
- The field name stands for ‘y pixels per EM'; this is the vertical size rounded to integer pixels of the EM square, which also is the vertical character pixel size, called
pixel_size_y
in the above example. - x_scale
- This is a 16.16 fixed-point scale to directly scale horizontal distances from design space to 1/64th of device pixels.
- y_scale
- This is a 16.16 fixed-point scale to directly scale vertical distances from design space to 1/64th of device pixels.
You can scale a distance expressed in font units to 26.6 pixel format directly with the help of the FT_MulFix
function.
Alternatively, you can also scale the value directly by using doubles.
b. Accessing Design Metrics (Glyph & Global)
You can access glyph metrics in font units simply by specifying the FT_LOAD_NO_SCALE
bit flag in FT_Load_Glyph
or FT_Load_Char
. The metrics returned in face->glyph->metrics
will all be in font units.
You can access unscaled kerning data using the FT_KERNING_MODE_UNSCALED
mode.
Finally, a few global metrics are available directly in font units as fields of the FT_Face
handle, as described in section 3 of this part.
Conclusion
This is the end of the second part of the FreeType tutorial. You are now able to access glyph metrics, manage glyph images, and render text much more intelligently (kerning, measuring, transforming & caching); this is sufficient knowledge to build a pretty decent text service on top of FreeType.
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.