From Xlib...

Xlib datatypes do not follow a naming convention. They are documented in Xlib - C Language Interface.

Xft uses these names: Bool, Colormap, Display, Drawable, Pixmap, Region, Visual, and XRectangle.

Some datatypes are especially relevant to Xft:

Drawable

Declared in <X11/X.h>, this is an X resource ID, e.g., a window associated with a display. Both windows and pixmaps can be used as sources and destinations in graphics operations. These windows and pixmaps are collectively known as drawables. However, an InputOnly window cannot be used as a source or destination in a graphics operation.

Region

Declared in <X11/Xutil.h> and <X11/Xregion.h>, a Region is an arbitrary set of pixel locations which Xlib can manipulate. Internally, a Region is represented by the union of an arbitrary number of rectangles. Xlib maintains a rectangle which tells it the extent of this union.

Visual

Declared in <X11/Xutil.h>, this structure contains information about the possible color mapping.

From XRender...

The X Render Extension library datatypes are inspired by Xlib, but lack the corresponding documentation. Refer to the header file for details:

or read the source code (which provides an outline of libXrender).

Xft uses these names: Picture, XGlyphInfo, XRenderColor.

From Fontconfig...

Fontconfig datatypes follow a naming convention, prefixing all names with “Fc” which are documented in Fontconfig Developers Reference.

Xft uses these Fontconfig names: FcBool, FcChar8, FcChar16, FcChar32, FcCharSet, FcEndian, FcFontSet, FcPattern, and FcResult.

From FreeType 2...

FreeType 2 datatypes follow a naming convention, prefixing all names with “FT_” which are documented in FreeType API Reference.

Xft uses these names: FT_Face, FT_Library, and FT_UInt.

FreeType 2 uses FT_UInt (an unsigned integer) to represent glyphs.

XftFont

typedef struct _XftFont {
	int	 ascent;
	int	 descent;
	int	 height;
	int	 max_advance_width;
	FcCharSet	*charset;
	FcPattern	*pattern;
} XftFont;

An XftFont is the primary data structure of interest to programmers using Xft; it contains general font metrics and pointers to the Fontconfig character set and pattern associated with the font.

XftFonts are populated with any of XftFontOpen(), XftFontOpenName(), XftFontOpenXlfd(), XftFontOpenInfo(), or XftFontOpenPattern(). XftFontCopy() is used to duplicate XftFonts, and XftFontClose() is used to mark an XftFont as unused. XftFonts are internally allocated, reference-counted, and freed by Xft; the programmer does not ordinarily need to allocate or free storage for them.

XftDrawGlyphs(), the XftDrawString*() family, XftDrawCharSpec(), and XftDrawGlyphSpec() use XftFonts to render text to an XftDraw object, which may correspond to either a core X drawable or an X Rendering Extension drawable.

XftGlyphExtents() and the XftTextExtents*() family are used to determine the extents (maximum dimensions) of an XftFont.

An XftFont's glyph or character coverage can be determined with XftFontCheckGlyph() or XftCharExists(). XftCharIndex() returns the XftFont-specific character index corresponding to a given Unicode codepoint.

XftGlyphRender(), XftGlyphSpecRender(), XftCharSpecRender(), and the XftTextRender*() family use XftFonts to draw into X Rendering Extension Picture structures.

Note: XftDrawGlyphs(), the XftDrawString*() family, XftDrawCharSpec(), and XftDrawGlyphSpec() provide a means of rendering fonts that is independent of the availability of the X Rendering Extension on the X server.

XftFontInfo

is an opaque object that stores information about a font. XftFontInfo structures are created with XftFontInfoCreate(), freed with XftFontInfoDestroy(), and compared with XftFontInfoEqual(). XftFontInfo objects are internally allocated and freed by Xft; the programmer does not ordinarily need to allocate or free storage for them.

Each XftFontInfo structure in use is associated with a unique identifier, which can be retrieved with XftFontInfoHash(). An XftFont can be opened based on XftFontInfo data with XftFontOpenInfo().

XftColor

typedef struct _XftColor {
	unsigned long	 pixel;
	XRenderColor	 color;
} XftColor;

An XftColor object permits text and other items to be rendered in a particular color (or the closest approximation offered by the X visual in use).

XftColorAllocName() and XftColorAllocValue() request a color allocation from the X server (if necessary) and initialize the members of XftColor. XftColorFree() instructs the X server to free the color currently allocated for an XftColor.

Once an XftColor has been initialized, XftDrawSrcPicture(), XftDrawGlyphs(), the XftDrawString*() family, XftDrawCharSpec(), XftDrawCharFontSpec(), XftDrawGlyphSpec(), XftDrawGlyphFontSpec(), and XftDrawRect() may be used to draw various objects using it.

XftDraw

is an opaque object which holds information used to render to an X drawable using either the core protocol or the X Rendering extension.

XftDraw objects are created with any of XftDrawCreate() (which associates an XftDraw with an existing X drawable), XftDrawCreateBitmap(), or XftDrawCreateAlpha(), and destroyed with XftDrawDestroy(). The X drawable associated with an XftDraw can be changed with XftDrawChange(). XftDraw objects are internally allocated and freed by Xft; the programmer does not ordinarily need to allocate or free storage for them.

The X Display, Drawable, Colormap, and Visual properties of an XftDraw can be queried with XftDrawDisplay(), XftDrawDrawable(), XftDrawColormap(), and XftDrawVisual(), respectively.

Several functions use XftDraw objects: XftDrawCharFontSpec(), XftDrawCharSpec(), XftDrawGlyphFontSpec(), XftDrawGlyphSpec(), XftDrawGlyphs(), XftDrawRect(), XftDrawSetClip(), XftDrawSetClipRectangles(), XftDrawSetSubwindowMode(), and the XftDrawString*() family.

The X Rendering Extension Picture associated with an XftDraw is returned by XftDrawPicture(), and XftDrawSrcPicture(). It is used by XftCharFontSpecRender(), XftCharSpecRender(), XftGlyphFontSpecRender(), XftGlyphRender(), XftGlyphSpecRender(), and the XftTextRender*() family.

XftCharSpec

typedef struct _XftCharSpec {
	FcChar32	 ucs4;
	short	 x;
	short	 y;
} XftCharSpec;

XftCharSpec is used by XftDrawCharSpec(), and XftCharSpecRender().

XftCharFontSpec

typedef struct _XftCharFontSpec {
	XftFont	*font;
	FcChar32	 ucs4;
	short	 x;
	short	 y;
} XftCharFontSpec;

XftCharFontSpec is used by XftCharFontSpecRender().

XftGlyphSpec

typedef struct _XftGlyphSpec {
	FT_UInt	  glyph;
	short	  x;
	short	  y;
} XftGlyphSpec;

XftGlyphSpec is used by XftDrawGlyphSpec().

XftGlyphFontSpec

typedef struct _XftGlyphFontSpec {
	XftFont	*font;
	FT_UInt	 glyph;
	short	 x;
	short	 y;
} XftGlyphFontSpec;

XftGlyphFontSpec is used by XftDrawGlyphFontSpec(), and XftGlyphFontSpecRender().

Initialization

A typical application using Xft does not explicitly initialize the library. That is usually done as a side-effect of opening a font.

When Xft initializes, it collects information about the display, and stores some of that information in a Fontconfig pattern (essentially a collection of properties with typed values). The calling application can modify that pattern to change the library's behavior.

Not all of the collected information is stored in a pattern. The remainder is stored in internal data structures. Xft makes some of that available to the application via functions.

Bool XftDefaultHasRender (

	Display	*dpy);

Obtain information about the display dpy if not done already, and return true if Xft found that the display supports the X Render extension, and if it is able to find a suitable XRenderPictFormat (X Render's datatype which is analogous to Xlib's Visual) on the display.

Bool XftDefaultSet (

	Display	*dpy,
	FcPattern	*defaults);

Obtain information about the display dpy if not done already, and set the Fontconfig pattern holding default properties which Xft will use for this display.

Xft uses those properties initially to obtain these limits:

Xft also uses these default properties in XftDefaultSubstitute().

void XftDefaultSubstitute (

	Display	*dpy,
	int	 screen,
	FcPattern	*pattern);

Xft fills in missing properties in the given pattern using default properties for the specified display dpy, e.g., as set in XftDefaultSet().

Typical Xft applications use this function to help Fontconfig choose a suitable font. These properties are substituted before calling FcDefaultSubstitute():

FcBool XftInit (

	_Xconst char	*config);

Initializes the Fontconfig library (calling FcInit()).

The config parameter is unused.

Xft does not deinitialize the Fontconfig library when it is done.

FcBool XftInitFtLibrary (void);

Initializes the FreeType library (calling FT_Init_FreeType() to create a library object) if it has not already been initialized. This is needed before using the FreeType library to read font data from a file.

Xft calls XftInitFtLibrary() internally via XftFontInfoCreate() and XftFontOpenPattern().

Xft does not discard the library object (e.g., using FT_Done_FreeType()) when it is done.

int XftGetVersion (void);

Return XftVersion, enabling an application to determine the actual version of Xft which is in use.

Opening and Matching Fonts

XftFont *XftFontOpen (

	Display	*dpy,
	int	 screen,
	...);

XftFontOpen takes a list of pattern element triples of the form field, type, value (terminated with a NULL), matches that pattern against the available fonts, and opens the matching font, sizing it correctly for screen number screen on display dpy. Return the matched font, or NULL if no match is found.

Example:

    font = XftFontOpen (dpy, screen,
                        XFT_FAMILY, XftTypeString, "charter",
                        XFT_SIZE, XftTypeDouble, 12.0,
                        NULL);

This opens the “charter” font at 12 points. The point size is automatically converted to the correct pixel size based on the resolution of the monitor.

XftFont *XftFontOpenName (

	Display	*dpy,
	int	 screen,
	_Xconst char	*name);

XftFontOpenName behaves as XftFontOpen does, except that it takes a Fontconfig pattern string (which is passed to the Fontconfig library's FcNameParse() function).

XftFont *XftFontOpenXlfd (

	Display	*dpy,
	int	 screen,
	_Xconst char	*xlfd)

XftFontOpenXlfd behaves as XftFontOpen does, except that it takes a string containing an X Logical Font Description (XLFD), and uses the XftXlfdParse() function.

FcPattern *XftFontMatch (

	Display	*dpy,
	int	 screen,
	_Xconst FcPattern	*pattern,
	FcResult	*result);

Also used internally by the XftFontOpen* functions, XftFontMatch can also be used directly to determine the Fontconfig font pattern resulting from an Xft font open request.

FcPattern *XftXlfdParse (

	_Xconst char	*xlfd_orig,
	Bool	ignore_scalable,
	Bool	complete);

XftXlfdParse parses the xlfd_orig parameter according to the X Logical Font Description Conventions document, but ignores some of the fields: setwidth_name, add_style_name, spacing, and average_width.

XftXlfdParse creates a Fontconfig pattern, setting the property XFT_XLFD to the xlfd_orig value, and maps the collected information to Fontconfig properties. Empty or “*” fields are ignored:

Families of Functions

Xft provides groups of drawing functions which differ according to the way the data is encoded, e.g., 8-bit (ISO-8859-1) versus UTF-8. Here is a summary of these related functions:

Determining Text Extents

Xft provides several functions for determining the required height and width for displaying a text-string. After accounting for the offset, in cases where the string will be shifted up, down, left or right, these numbers are referred to as text extents.

void XftTextExtents8 (

	Display	*dpy,
	XftFont	*font,
	_Xconst FcChar8	*string,
	int	 len,
	XGlyphInfo	*extents);

XftTextExtents8 computes the pixel extents on display dpy of no more than len glyphs of a string consisting of eight-bit characters when drawn with font, storing them in extents.

void XftTextExtents16 (

	Display	*dpy,
	XftFont	*font,
	_Xconst FcChar16	*string,
	int	 len,
	XGlyphInfo	*extents);

XftTextExtents16 computes the pixel extents on display dpy of no more than len glyphs of a string consisting of sixteen-bit characters when drawn with font, storing them in extents.

void XftTextExtents32 (

	Display	*dpy,
	XftFont	*font,
	_Xconst FcChar32	*string,
	int	 len,
	XGlyphInfo	*extents);

XftTextExtents32 computes the pixel extents on display dpy of no more than len glyphs of a string consisting of thirty-two-bit characters when drawn with font, storing them in extents.

void XftTextExtentsUtf8 (

	Display	*dpy,
	XftFont	*font,
	_Xconst FcChar8	*string,
	int	 len,
	XGlyphInfo	*extents);

XftTextExtentsUtf8 computes the pixel extents on display dpy of no more than len bytes of a UTF-8 encoded string when drawn with font, storing them in extents.

void XftTextExtentsUtf16 (

	Display	*dpy,
	XftFont	*font,
	_Xconst FcChar8	*string,
	FcEndian	 endian,
	int	 len,
	XGlyphInfo	*extents);

XftTextExtentsUtf16 computes the pixel extents on display dpy of no more than len bytes of a UTF-16LE- or UTF-16BE-encoded string when drawn with font, storing them in extents. The endianness of string must be specified in endian.

void XftGlyphExtents (

	Display	*dpy,
	XftFont	*font,
	_Xconst FT_UInt	*glyphs,
	int	 nglyphs,
	XGlyphInfo	*extents);

Also used internally by the XftTextExtents*() functions, XftGlyphExtents computes the pixel extents on display dpy of no more than nglyphs in the array glyphs drawn with font, storing them in extents.

If any of the glyphs are missing (determined by a check with XftFontCheckGlyph()), the corresponding entry in extents is filled with zeroes.

Managing XftColor

Bool XftColorAllocName (

	Display	*dpy,
	_Xconst Visual	*visual,
	Colormap	 cmap,
	_Xconst char	*name,
	XftColor	*result);

Use XAllocNamedColor() to look up the named color name for the screen associated with the colormap cmap.

The visual parameter is unused.

Bool XftColorAllocValue (

	Display	*dpy,
	Visual	*visual,
	Colormap	 cmap,
	_Xconst XRenderColor	*color,
	XftColor	*result);

Allocate a color value:

void XftColorFree (

	Display	*dpy,
	Visual	*visual,
	Colormap	 cmap,
	XftColor	*color);

If the visual class is not TrueColor, Xft calls XFreeColors() to free the entry from the colormap cmap whose pixel value in the color parameter was allocated by XftColorAllocName().

Managing XftDraw

XftDraw *XftDrawCreate (

	Display	*dpy,
	Drawable	 drawable,
	Visual	*visual,
	Colormap	 colormap);

XftDrawCreate creates a structure that can be used to render text and rectangles using the specified drawable, visual, and colormap on display.

XftDraw *XftDrawCreateBitmap (

	Display	*dpy,
	Pixmap	 bitmap);

XftDrawCreateBitmap behaves as XftDrawCreate(), except that it uses an X pixmap of color depth 1 instead of an X drawable.

XftDraw * XftDrawCreateAlpha (

	Display	*dpy,
	Pixmap	 pixmap,
	int	 depth);

XftDrawCreateAlpha behaves as XftDrawCreate(), except that it uses an X pixmap of color depth depth instead of an X drawable.

void XftDrawChange (

	XftDraw	*draw,
	Drawable	 drawable);

XftDrawChange changes the X drawable association of the existing Xft draw object draw from its current value to drawable.

Display *XftDrawDisplay (

	XftDraw	*draw);

XftDrawDisplay returns a pointer to the display associated with the Xft draw object draw.

Drawable XftDrawDrawable (

	XftDraw	*draw);

XftDrawDrawable returns the X drawable associated with the Xft draw object draw.

Colormap XftDrawColormap (

	XftDraw	*draw);

XftDrawColormap() returns the colormap associated with the Xft draw object draw.

Visual *XftDrawVisual (

	XftDraw	*draw);

XftDrawVisual returns a pointer to the visual associated with the Xft draw object draw.

Picture XftDrawPicture (

	XftDraw	*draw);

XftDrawPicture returns the picture associated with the Xft draw object draw.

If the the X server does not support the X Rendering Extension, 0 is returned.

Picture XftDrawSrcPicture (

	XftDraw	*draw,
	_Xconst XftColor	*color);

Return an X Render Picture object, which is used for rendering glyphs, e.g., with XftGlyphRender(), XftGlyphSpecRender(), or XftGlyphFontSpecRender(), by XftDrawGlyphs(), XftDrawGlyphSpec(), XftDrawGlyphFontSpec(), respectively.

If the X server does not support the X Render extension, those functions use XftGlyphCore(), XftGlyphSpecCore(), or XftGlyphFontSpecCore().

void XftDrawDestroy (

	XftDraw	*draw);

XftDrawDestroy destroys draw (created by one of the XftDrawCreate*() functions) and frees the memory that was allocated for it.

Bool XftDrawSetClip (

	XftDraw	*draw,
	Region	 r);

Set up clipping for the given XftDraw parameter draw starting with a Region:

XftDrawSetClip() returns True if no change was necessary, or if the operation succeeded. It returns False if it was unable to create the new Region().

Bool XftDrawSetClipRectangles (

	XftDraw	*draw,
	int	 xOrigin,
	int	 yOrigin,
	_Xconst XRectangle	*rects,
	int	 n);

Like XftDrawSetClip(), XftDrawSetClipRectangles() sets up clipping for the given XftDraw parameter draw but uses a set of n rectangles (the rects parameter) which could be used to construct a Region .

Xft sets the clip_type for draw to XftClipTypeRectangles and uses XSetClipRectangles() for core (X11) clipping and XRenderSetPictureClipRectangles() for X Render clipping.

void XftDrawSetSubwindowMode (

	XftDraw	*draw,
	int	 mode);

Sets the subwindow-mode for the given XftDraw parameter draw. The mode can be either ClipByChildren (the default), or IncludeInferiors:

In addition to the subwindow-mode maintained by Xft, it updates the subwindow mode for any associated graphics context GC using XSetSubwindowMode() as well as for an X Render Picture using XRenderChangePicture().

Drawing Strings

void XftDrawString8 (

	XftDraw	*d,
	_Xconst XftColor	*color,
	XftFont	*font,
	int	 x,
	int	 y,
	_Xconst FcChar8	*string,
	int	 len);

XftDrawString8 draws no more than len glyphs of string to Xft drawable d using font in color at position x, y.

Drawing Other Things

void XftDrawRect (

	XftDraw	*d,
	_Xconst XftColor	*color,
	int	 x,
	int	 y,
	unsigned int	 width,
	unsigned int	 height);

XftDrawRect draws a solid rectangle of the specified color, width, and height at position x, y to Xft drawable d.

void XftCharFontSpecRender (

	Display	*dpy,
	int	 op,
	Picture	 src,
	Picture	 dst,
	int	 srcx,
	int	 srcy,
	_Xconst XftCharFontSpec	*chars,
	int	 len);

XftCharFontSpecRender() converts the chars parameter from XftCharFontSpec to XftGlyphFontSpec, passing the converted array along with the other parameters unchanged to XftGlyphFontSpecRender() to render the data.

void XftDrawGlyphFontSpec (

	XftDraw	*draw,
	_Xconst XftColor	*color,
	_Xconst XftGlyphFontSpec	*glyphs,
	int	 len);

Draw a list of glyphs associated with fonts at specified coordinates, passed as an array of len XftGlyphFontSpec structures via the parameter glyphs. All of the glyphs are drawn using the color specified in the color parameter.

For each entry in the glyphs array:

void XftGlyphFontSpecRender (

	Display	*dpy,
	int	 op,
	Picture	 src,
	Picture	 dst,
	int	 srcx,
	int	 srcy,
	_Xconst XftGlyphFontSpec	*glyphs,
	int	 nglyphs);

This involves several steps:

Manipulating patterns

FcFontSet *XftListFonts (

	Display	*dpy,
	int	 screen,
	...);

Xft uses FcPatternVapBuild() and FcObjectSetVapBuild() to process the variable-length parameter list, and FcFontList() to obtain a list of matching Fontconfig patterns, which it returns to the caller. The caller can dispose of the return value using FcPatternDestroy().

FcPattern *XftNameParse (

	_Xconst char	*name);

Xft uses Fontconfig to parse the name, passing the name to FcNameParse(), returning the result.

FcBool XftNameUnparse (

	FcPattern	*pat,
	char	*dest,
	int	 len);

Like XfgNameParse(), Xft uses Fontconfig. In this case, it uses FcNameUnparse(), which converts the pattern pat back into a string that can be parsed. XftNameUnparse() stores the result via the caller's pointer dest, but checks first if it will fit, using the len parameter. If it fits, Xft copies the string and returns FcTrue, otherwise it returns FcFalse.

Manipulating Font data

void XftFontLoadGlyphs (

	Display	*dpy,
	XftFont	*pub,
	FcBool	 need_bitmaps,
	_Xconst FT_UInt	*glyphs,
	int	 nglyph);

Using FT_Load_Glyph(), load nglyphs for the glyph indices (Unicode values) listed in the array glyphs from the given font pub.

Loading a glyph entails more than just reading data into memory. Xft uses the Fontconfig pattern associated with the display dpy (e.g., via XftDefaultSet()) to determine whether to use a bounding box, clip the glyphs into those bounds, scale the glyphs, compute font metrics, and add it to the X Render extension using XRenderAddGlyphs().

void XftFontUnloadGlyphs (

	Display	*dpy,
	XftFont	*pub,
	_Xconst FT_UInt	*glyphs,
	int	 nglyph);

Discards data for up to nglyph glyphs whose glyph indices (Unicode values) are listed in the array glyphs for the given font pub. If the glyphs were added to the X Render extension, Xft removes those using XRenderFreeGlyphs(). Xft keeps track of the amount of memory used for glyphs, and updates the usage associated with the display dpy.

FT_Face XftLockFace (

	XftFont	*pub);

If no FreeType 2 “face” (in-memory representation of a given typeface in a given style) has been created for the pub font, create one using FT_New_Face(). Face-locks are a reference count used by Xft to ensure that only one face is created, and that it is retained until the font is no longer used.

Face-locking is used directly in XftCharIndex() and XftFontLoadGlyphs(), which in turn are used in many functions of Xft.

Face-locking was introduced in version 1 (October 2002). A few applications, such as Gdk/Gimp relied upon these functions. In version 2.1.9 (June 2006), face-locking was retained as part of the public API when improved shared-library configurations provided for hiding private symbols.

void XftUnlockFace (

	XftFont	*pub);

Decrements the reference count for the FreeType 2 “face” associated with the font.

FT_Face objects are deallocated using FT_Done_Face(). Xft does this in XftFontInfoDestroy() and when cleaning up on failure in XftFontInfoCreate() and XftFontOpenPattern().

Xft 1.x Header File

#include <X11/Xft/XftCompat.h>

Xft 1.x Data Types

XftPattern

holds a set of names with associated value lists; each name refers to a property of a font. XftPatterns are used as inputs to the matching code as well as holding information about specific fonts.

XftFontSet

contains a list of XftPatterns. Internally, Xft uses this data structure to hold sets of fonts. Externally, Xft returns the results of listing fonts in this format.

XftObjectSet

holds a set of names and is used to specify which fields from fonts are placed in the the list of returned patterns when listing fonts.