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Derived from: none
Declared in: be/interface/Font.h
Library: libbe.so
A BFont object records a set of font attributes, such as the font's family, style, size, and so on. You can set most of these attributes to modify the font and then use the object to set the font of a BView. A BView's font determines how the characters that it draws (with the DrawString() and DrawChar() functions) will be rendered.
A BFont object can perform calculations based on the metrics of the particular font it represents. For example, it can tell you how much screen real estate it needs to display a given line of text.
To find which fonts are currently installed on the system, call get_font_family() and get_font_style().
A BFont object by itself doesn't do anything. To be able to draw characters in the font, the object must be passed to BView's SetFont() function (or BTextView's SetFontAndColor()).
A BFont object is always a full representation of a font; all attributes are always set. However, you can choose which of these attributes will modify a BView's current font by passing a mask to SetFont() (or SetFontAndColor()). For example, this code sets only the font shear and spacing:
BFont font; font.SetShear(60.0); font.SetSpacing(B_CHAR_SPACING); myView->SetFont(&font, B_FONT_SHEAR | B_FONT_SPACING);
Alternatively, the BView's font could have been modified and reset as follows:
BFont font; myView->GetFont(&font); font.SetShear(60.0); font.SetSpacing(B_CHAR_SPACING); myView->SetFont(&font);
Notice that we had to explicitly reset the view's font (through SetFont()) after changing the font's attributes.
The Interface Kit constructs three BFont objects (plain, bold, and fixed)for each application when the application starts up. The values of these fonts are set by the user through the FontPanel preferences application. You can get to these objects through global pointers :
const BFont *
be_plain_font
The font that's used to display most gadgets in the user interface, such as check box labels and menu items. All BControl objects use this font.
const BFont *
be_bold_font
The font that's used to display window titles and BBox labels.
const BFont *
be_fixed_font
The font that's used to display fixed-width characters.
The global fonts are const objects that can't be modified by your application, and aren't updated by the system, even if the user changes their definitions while your app is running. The new values take effect the next time your application is launched.
To use a system font in a view, simply call SetFont():
myView->SetFont(be_bold_font);
If you want to modify some attributes of a system font, you have to make a copy of it first (and modify the copy):
BFont font(be_bold_font); font.SetSize(13.0); myView->SetFont(&font);
Applications should respect the user's choices and base all font choices on these three system fonts, rather than hard-code font names into the application. You should not try to predict the fonts that will be installed on the user's machine.
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Initializes the new BFont object as a copy of another font. If no font is specified, be_plain_font is used.
The system BFont objects, including be_plain_font, are initialized only when you create a BApplication object for your application. Therefore, the default settings of BFont objects constructed before the BApplication object will be invalid.
See also: BView::SetFont(), BTextView::SetFontAndColor()
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Returns a unicode_block object that identifies which Unicode blocks the font supports. You can then use the unicode_block::Includes() function to determine if specific blocks are supported.
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Returns a BRect that can enclose the entire font in its current style and size.
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Direction() returns a font_direction constant that describes the direction in which the object's text is meant to be read:
| B_FONT_LEFT_TO_RIGHT |
| B_FONT_RIGHT_TO_LEFT |
This is an inherent property of the font and cannot be set.
The direction of the font affects the direction in which DrawString() draws the characters in a string, but not the direction in which it moves the pen.
See also: BView::DrawString()
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Returns the file format of the font (ie, whether it's a PostScript or TrueType font).
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GetBoundingBoxesAsGlyphs() returns an array of BRect objects indicating the bounding rectangles of all the characters in an array. Each BRect returned corresponds to one character's glyph.
GetBoundingBoxesAsString() returns an array of BRect objects indicating the bounding rectangles of each character in a string.
GetBoundingBoxesForStrings() returns an array of BRect objects indicating the bounding rectangles for an array of strings, one BRect per string. These rectangles enclose the entire string they represent.
In all cases, the mode indicates whether the rectangles should be returned in the screen's metric (B_SCREEN_METRIC), or in printing metrics (B_PRINTING_METRIC).
The delta argument for GetBoundingBoxesAsString() and the deltas argument for GetBoundingBoxesForStrings() indicate escapement deltas that should be applied when making the bounding box calculations. This lets you indicate that the characters should be closer together or further apart than normal, for example.
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These two functions provide the information required to precisely position characters on the screen or printed page. For each character passed in the charArray, they write information about the horizontal dimension of the character into the escapementArray or the edgeArray. Both functions provide this information in "escapement units" that yield standard coordinate units (72.0 per inch) when multiplied by the font size.
GetEscapements() and GetEdges() expect the character array they're passed to contain at least numChar characters; neither function checks the charArray for a null terminator. Because the array may hold multibyte characters (in B_UNICODE_UTF8 encoding), the number of bytes in the array may be greater than the number of characters specified. The escapementArray and edgeArray should be long enough to hold an output value for every input character.
You can optionally request that escapement information be returned as an array of BPoint objects.
A character's escapement measures the amount of horizontal space it requires. It includes the space needed to display the character itself, plus some extra room on the left and right edges to separate the character from its neighbors. The illustration below shows the approximate escapements for the letters 'l' and 'p'; the escapement for each character is the distance between the vertical lines:
GetEscapements() measures the same space that functions such as StringWidth() and BTextView's LineWidth() do, but it measures each character individually and records its width in per-point-size escapement units. To translate the escapement value to the width of the character, you must multiply by the point size of the font:
float width = escapementArray[i] * font.Size();
Because of rounding errors, there may be some difference between the value returned by StringWidth() and the width calculated from the individual escapements of the characters in the string.
The versions of GetEscapements() that use BPoints for the escapement value use the BPoint escapementArray to indicate a vector by which the pen is moved after drawing a character (this lets the escapement indicate both an X and a Y adjustment; the Y might need to be adjusted if the font is rotated, for example). The offsetArray is applied by the dynamic spacing in order to improve the relative position of the character's width with relation to another character, without altering the width.
The escapement value is scalable if the spacing mode of the font is B_CHAR_SPACING. In other words, given B_CHAR_SPACING and the same set of font characteristics, GetEscapements() will report the same measurement for a character regardless of the font size. You can cache one value per character and use it for all font sizes. For the other spacing modes, the reported escapement depends on the font size and therefore can't be scaled.
For most spacing modes, a character has a constant escapement in all contexts; it depends only on the font. However, for B_STRING_SPACING, each character's escapement is also contextually dependent on the string it's in. To find the escapement of a character within a particular string, you must pass the entire string in the input charArray.
In the B_BITMAP_SPACING and B_FIXED_SPACING modes, all characters have integral widths (without a fractional part). For these modes, multiplying an escapement by the font size should yield an integral value. In B_FIXED_SPACING mode, all characters have the same escapement.
If a delta argument is provided, GetEscapements() will adjust the escapements it reports so that, after multiplying by the font size, the character widths will include the specified increments. An escapement_delta structure contains two values:
float nonspace
The amount to add to the width of each character with a visible glyph.
float space
The amount to add to each whitespace character (characters like B_TAB and B_SPACE with an escapement but no visible glyph).
A similar argument can be passed to BView's DrawString() to adjust the spacing of the characters as they're drawn.
Edge values measure how far a character outline is inset from its left and right escapement boundaries. GetEdges() places the edge values into an array of edge_info structures. Each structure has a left and a right data member, as follows:
typedef struct {
float left;
float right;
} edge_info
Edge values, like escapements, are stated in per-point-size units that need to be multiplied by the font size.
The illustration below shows typical character edges. As in the illustration above, the solid vertical lines mark escapement boundaries. The dotted lines mark off the part of each escapement that's an edge, the distance between the character outline and the escapement boundary:
This is the normal case. The left edge is a positive value measured rightward from the left escapement boundary. The right edge is a negative value measured leftward from the right escapement boundary.
However, if the characters of a font overlap, the left edge can be a negative value and the right edge can be positive. This is illustrated below:
Note that the italic 'l' extends beyond its escapement to the right, and that the 'p' begins before its escapement to the left. In this case, instead of separating the adjacent characters, the edges determine how much they overlap.
Edge values are specific to each character and depend on nothing but the character and the font. They don't take into account any contextual information; for example, the right edge for italic 'l' would be the same no matter what letter followed. Edge values therefore aren't sufficient to decide how character pairs can be kerned. Kerning is contextually dependent on the combination of two particular characters.
See also: StringWidth(), SetSpacing()
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Given an array of characters, charArray, which contains numChars characters, and an array of BShape objects, glyphShapeArray, this function makes each element in the glyphShapeArray describe the shape of the corresponding glyph in the charArray.
This lets you create BShape objects in the shape of the outline of a font. You can then manipulate these BShapes to do interesting text effects.
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Fonts are drawn one pixel above the logical baseline; this affects BShape objects derived from fonts, too. The fonts are also one pixel above the baseline in the BShapes this function returns. If you want to apply a transform to these shapes, be sure to remove the offset before applying the transform, then add the offset back to the points before drawing the shape, or you won't get the expected results.
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Given an array of characters in charArray (of which there are numChars members), this function fills out the array of booleans specified by hasArray such that each entry in hasArray is true if the corresponding character in charArray has a glyph in the font, and false if the character doesn't have a glyph.
This way, you can determine if you can use one or more characters without the user seeing "no glyph" symbols.
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GetHeight() writes the three components that determine the height of the font into the structure that the height argument refers to. A font_height structure has the following fields:
float
ascent
How far characters can ascend above the baseline.
float
descent
How far characters can descend below the baseline.
float
leading
How much space separates lines (the distance between the descent of the line above and the ascent of the line below).
If you need to round the font height, or any of its components, to an integral value (to figure the spacing between lines of text on-screen, for example), you should always round them up to reduce the amount of vertical character overlap.
See also: BView::GetFontHeight()
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GetTruncatedStrings() Ttruncates a set of strings so that each one (and an ellipsis to show where the string was cut) will fit into the maxWidth horizontal space. This function is useful for shortening long strings that are displayed to the user—for showing path names in a list, for example.
The numStrings argument states how many strings in the inputStringArray should be shortened. The mode argument states where the string should be cut. It can be:
| B_TRUNCATE_BEGINNING | Cut from the beginning of the string until it fits within the specified width. |
| B_TRUNCATE_MIDDLE | Cut from the middle of the string. |
| B_TRUNCATE_END | Cut from the end of the string. |
| B_TRUNCATE_SMART | Cut anywhere, but do so intelligently, so that all the strings remain different after being cut. For example, if a set of similar path names are passed in the inputStringArray, this mode would attempt to cut from the identical parts of the path names and preserve the parts that are different. This mode also pays attention to word boundaries, separators, punctuation, and the like. However, it's not implemented for the current release. |
Each output string is written to the truncatedStringArray—into memory that the caller must provide—at an index that matches the index of the full string in the inputStringArray. The truncatedStringArray is a list of pointers to string buffers. Each buffer should be allocated separately and should be at least 3 bytes longer than the matching input string. The 3 bytes allow for the worst-case scenario: GetTruncatedStrings() cuts a one-byte character from the input string and replaces it with an ellipsis character, which takes three bytes in UTF-8 encoding, for a net gain of 2 bytes. It then adds a null terminator for the third byte.
TruncateString() truncates the BString inOutString to be no longer than the width specified by maxWidth, using the given truncation mode.
The output strings are null-terminated. The input strings should likewise be null-terminated.
See also: StringWidth()
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These functions are used to get information about fonts that have been "tuned" to look good when displayed on-screen. A tuned font is a set of character bitmaps, originally produced from the standard outline font and then modified so that the characters are well proportioned and spaced when displayed at the low resolution of the screen (1 pixel per point).
Because it's a bitmap font, a tuned font captures a specific configuration of font attributes, including size, style, shear, and rotation. A tuned font is a counterpart to an outline font with the same settings. If a BView's current font has a tuned counterpart, DrawString() automatically chooses it when drawing on-screen. Tuned fonts are not used for printing.
CountTuned() returns how many tuned fonts there are for the family and style represented by the BFont object. GetTunedInfo() writes information about the tuned font at index into the structure the info argument refers to. Indices begin at 0 and count only tuned fonts for the BFont's family and style.
With this information, you can set the BFont to values that match those of a tuned font. When a BView draws to the screen, it picks a tuned font if there's one that corresponds to its current font in all respects.
See also: get_font_family()
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Returns true if the font is fixed; false otherwise.
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This function is not yet supported.
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Writes the following information about the font to the standard output (on a single line):
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These functions set and return the encoding that maps character values to characters. The following encodings are supported:
| B_UNICODE_UTF8 (UTF-8) | B_ISO_8859_6 (Latin/Arabic) |
| B_ISO_8859_1 (Latin 1) | B_ISO_8859_7 (Latin/Greek) |
| B_ISO_8859_2 (Latin 2) | B_ISO_8859_8 (Latin/Hebrew) |
| B_ISO_8859_3 (Latin 3) | B_ISO_8859_9 (Latin 5) |
| B_ISO_8859_4 (Latin 4) | B_ISO_8859_10 (Latin 6) |
| B_ISO_8859_5 (Latin/Cyrillic) | B_MACINTOSH_ROMAN |
UTF-8 is an 8-bit encoding for Unicode and is part of the Unicode standard. It matches ASCII values for all 7-bit character codes, but uses multibyte characters for values over 127. The other encodings take only a single byte to represent a character; they therefore necessarily encompass a far smaller set of characters. Most of them represent standards in the ISO/IEC 8859 family of character codes that extend the ASCII set. B_MACINTOSH_ROMAN stands for the standard encoding used by the Mac OS.
The encoding affects both input and output functions of the BView. It determines how DrawString() interprets the character values it's passed and also how KeyDown() encodes character values for the keys the user pressed.
UTF-8 is the preferred encoding and the one that's most compatible with objects defined in the software kits. For example, a BTextView expects all text it takes from the clipboard or from a dragged and dropped message to be UTF-8 encoded. If it isn't, the results are not defined. The more that applications stick with UTF-8 encoding, the more freely they'll be able to exchange data.
See also: "Character Encoding" on page48 of this chapter, convert_to_utf8(), BView::DrawString(), BView::KeyDown()
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These functions set and return a mask that record secondary characteristics of the font, such as whether characters are underlined or drawn in outline. The values that form the face mask are:
B_ITALIC_FACE
Characters are drawn italicized.
B_UNDERSCORE_FACE
Characters are drawn underlined.
B_NEGATIVE_FACE
Characters are drawn in the low color, while the background is drawn in the high color.
B_OUTLINED_FACE
Characters are drawn hollow, with a line around their border, but unfilled.
B_STRIKEOUT_FACE
Characters are drawn "struck-out," with a line drawn horizontally through the middle.
B_BOLD_FACE
Characters are drawn in boldface.
B_REGULAR_FACE
Characters are drawn normally.
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Sets the family and face of the font. The family passed to this function must be one of the families enumerated by the get_font_family() global function and face must be a combination of the face values described under SetFace() on page125. If the family is NULL, SetFamilyAndFace() sets only the face.
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SetFamilyAndStyle() sets the family and style of the font. The family passed to this function must be one of the families enumerated by the get_font_family() global function and style must be one of the styles associated with that family, as reported by get_font_style(). If the family is NULL, SetFamilyAndStyle() sets only the style; if style is NULL, it sets only the family.
GetFamilyAndStyle() writes the names of the current family and style into the font_value and font_style variables provided.
Internally, the BFont class encodes each family and style combination as a unique integer. FamilyAndStyle() returns that code, which can then be passed to SetFamilyAndStyle() to set another BFont object. The integer code is not persistent; its meaning may change when the list of installed fonts changes and when the machine is rebooted.
See also: get_font_family()
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These functions set and return a mask that records various behaviors of the font. There are two flags: B_DISABLE_ANTIALIASING, which turns off all antialiasing for characters displayed in the font, and B_FORCE_ANTIALIASING, which forces all font rendering to be anti-aliased. The default mask has antialiasing turned on.
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These functions set and return the rotation of the baseline for characters displayed in the font. The baseline rotates counterclockwise from an axis on the left side of the character. The default (horizontal) baseline is at 0 °. For example, this code
BFont font;
font.SetRotation(45.0);
myView->SetFont(&font, B_FONT_ROTATION);
myView->DrawString("to the northeast");
would draw a string that extended upwards and to the right.
Rotation is not supported by some Interface Kit classes, including BTextView.
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These functions set and return the angle at which characters are drawn relative to the baseline. The default (perpendicular) shear for all font styles, including oblique and italic ones, is 90.0 °. The shear is measured counterclockwise and can be adjusted within the range 45.0 ° (slanted to the right) through 135.0 ° (slanted to the left). If the shear passed falls outside this range, it will be adjusted to the closest value within range.
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These functions set and return the size of the font in points. Valid sizes range from less than 1.0 point through 10,000 points.
See also: BView::SetSize()
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These functions set and return the mode that determines how characters are horizontally spaced relative to each other when they're drawn. The mode also affects the width or "escapement" of each character as reported by GetEscapements().
There are four spacing modes:
B_CHAR_SPACING
Positions each character according to its own inherent width, without adjustment. This produces good results on high-resolution devices like printers, and is the best mode to use for printing. However, when character widths are rounded for the screen, the results are generally poor. Characters are not well-separated and can collide or overlap at small font sizes.
B_STRING_SPACING
Keeps the string at the same width as it would have for B_CHAR_SPACING, but optimizes the position of each character within that space. The position of a character depends on the surrounding characters and the overall width of the string. Collisions are unlikely in this mode, but because the width of the string constrains what can be done, characters may touch each other.
This mode is preferred when it's important to have the screen match the printed page—for example, to have lines break on-screen where they will break when the display is printed. As the user types new characters into a line of text, the application must redraw the entire line to add each character. The characters in the line may therefore appear to "jiggle" or jump around as new ones are added. New optimal positions are calculated for each character as the width and composition of the string changes.
B_BITMAP_SPACING
Calculates the width of each character according to its bitmap appearance on-screen. The widths are chosen for optimal spacing, so that characters never collide and rarely touch. This mode increases the B_CHAR_SPACING width of a string if necessary to keep characters separated. (For a small-sized bold font, it may increase the string width substantially.)
In this mode, the spacing between characters is regular and not contextually dependent. Character widths are integral values. This is the best mode for drawing small amounts of text in the user interface; it's the mode that BTextView objects use and it works for both proportional and fixed-width fonts. However, the spacing of text shown on-screen won't correspond to the spacing when the text is printed in B_CHAR_SPACING mode.
B_FIXED_SPACING
Positions characters according to a constant, integral width. This mode can only be used with fixed-width fonts (fonts with the B_IS_FIXED flag set); trying to use B_FIXED_SPACING on other fonts will result in B_CHAR_SPACING being used by default. All characters have the same escapement.
The B_CHAR_SPACING mode is the preferred mode for printing. It's also somewhat faster than B_STRING_SPACING or B_BITMAP_SPACING. In all modes other than B_STRING_SPACING, it's possible to change the character displayed at the end of a string by erasing it and drawing a new character. However, in B_STRING_SPACING mode, it's necessary to erase the entire string and redraw it. The longer the string, the better the results.
The B_STRING_SPACING and B_BITMAP_SPACING modes are relevant only for font sizes in a range of about 7.0 points to 18.0 points. Above that range, B_CHAR_SPACING achieves reasonable results on-screen and may be used even where one of the other two modes is specified. Below that range, the screen resolution isn't great enough for the different modes to produce significantly different results, so again B_CHAR_SPACING is used.
In addition, B_CHAR_SPACING is always used for rotated or sheared text and when antialiasing is disabled.
See also: BView::DrawString(), GetEscapements()
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StringWidth() returns how much room is required to draw a string in the font. It measures the characters encoded in length bytes of the string—or, if no length is specified, the entire string up to the null character, '0', which terminates it. The return value totals the width of all the characters in coordinate units; it's the length of the baseline required to draw the string.
GetStringWidth() provides the same information for a group of strings. It works its way through the stringArray looking at a total of numStrings. For each string, it gets the length at the corresponding index from the lengthArray and places the width of the string in the widthArray at the same index.
These functions take all the attributes of the font—including family, style, size, and spacing—into account.
See also: BView::StringWidth()
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Assigns one BFont object to another. After the assignment, the two objects are identical to each other and do not share any data.
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These operators test whether two BFont objects are identical in all respects. If all settable font attributes are the same in both objects, they're equal. If not, they're unequal.
Declared in: <be/interface/Font.h>
| Constant | Description |
|---|---|
| B_SCREEN_METRIC | The screen metric. |
| B_PRINTING_METRIC | The printing metric. |
The font_metric_mode constants above indicate whether a font calculation should be done with the screen or the printer in mind.
Declared in: <be/interface/Font.h>
| Constant | Description |
|---|---|
| B_TRUETYPE_WINDOWS | Microsoft Windows format TrueType font. |
| B_POSTSCRIPT_TYPE1_WINDOWS | Microsoft Windows format PostScript Type 1 font. |
The font_file_format constants are used to specify what type of file a font was loaded from. Currently, only Microsoft Windows-format TrueType and PostScript Type 1 fonts are supported.
<be/interface/Font.h>
class unicode_block {
public:
inline unicode_block();
inline unicode_block(uint64 block2, uint64 block1);
inline bool Includes(const unicode_block &block) const;
inline unicode_block operator&(const unicode_block &block) const;
inline unicode_block operator|(const unicode_block &block) const;
inline unicode_block &operator=(const unicode_block &block);
inline unicode_block operator==(const unicode_block &block) const;
inline unicode_block operator!=(const unicode_block &block) const;
private:
fData[2];
};
The unicode_block class describes the ranges of Unicode characters a font supports. You can get a unicode_block object for a font by calling the Blocks() function. Once you have this, you can check to see if a particular block is supported, or compare it to another block to see if it's inclusive, equal, unequal, and so forth.
In general, you won't instantiate a unicode_block object on your own.
The unicode_block::Includes() function lets you determine if another block is a subset of the unicode_block object.
There are a number of predefined Unicode blocks, as follows:
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