NAME¶
Font::FreeType::Glyph - glyphs from font typefaces loaded from Font::FreeType
SYNOPSIS¶
use Font::FreeType;
my $freetype = Font::FreeType->new;
my $face = $freetype->face('Vera.ttf');
$face->set_char_size(24, 24, 100, 100);
my $glyph = $face->glyph_from_char('A');
my $glyph = $face->glyph_from_char_code(65);
# Render into an array of strings, one byte per pixel.
my ($bitmap, $left, $top) = $glyph->bitmap;
# Read vector outline.
$glyph->outline_decompose(
move_to => sub { ... },
line_to => sub { ... },
conic_to => sub { ... },
cubic_to => sub { ... },
);
DESCRIPTION¶
This class represents an individual glyph (character image) loaded from a font.
See Font::FreeType::Face for how to obtain a glyph object, in particular the
"glyph_from_char_code()" and "glyph_from_char()" methods.
Things you an do with glyphs include:
- •
- Get metadata about the glyph, such as the size of its image and other
metrics.
- •
- Render a bitmap image of the glyph (if it's from a vector font) or extract
the existing bitmap (if it's from a bitmap font), using the
"bitmap()" method.
- •
- Extract a precise description of the lines and curves that make up the
glyph's outline, using the "outline_decompose()" method.
For a detailed description of the meaning of glyph metrics, and the structure of
vectorial outlines, see
<
http://freetype.sourceforge.net/freetype2/docs/glyphs/>
METHODS¶
Unless otherwise stated, all methods will die if there is an error, and the
metrics are scaled to the size of the font face.
- bitmap([render-mode])
- If the glyph is from a bitmap font, the bitmap image is returned. If it is
from a vector font, then the outline is rendered into a bitmap at the
face's current size.
Three values are returned: the bitmap itself, the number of pixels from the
origin to where the left of the area the bitmap describes, and the number
of pixels from the origin to the top of the area of the bitmap (positive
being up).
The bitmap value is a reference to an array. Each item in the array
represents a line of the bitmap, starting from the top. Each item is a
string of bytes, with one byte representing one pixel of the image,
starting from the left. A value of 0 indicates background (outside the
glyph outline), and 255 represents a point inside the outline.
If antialiasing is used then shades of grey between 0 and 255 may occur.
Antialiasing is performed by default, but can be turned off by passing the
"FT_RENDER_MODE_MONO" option.
The size of the bitmap can be obtained as follows:
my ($bitmap, $left, $top) = $glyph->bitmap;
my $width = length $bitmap->[0];
my $height = @$bitmap;
The optional "render_mode" argument can be any one of the
following:
- FT_RENDER_MODE_NORMAL
- The default. Uses antialiasing.
- FT_RENDER_MODE_LIGHT
- Changes the hinting algorithm to make the glyph image closer to it's real
shape, but probably more fuzzy.
Only available with Freetype version 2.1.4 or newer.
- FT_RENDER_MODE_MONO
- Render with antialiasing disabled. Each pixel will be either 0 or
255.
- FT_RENDER_MODE_LCD
- Render in colour for an LCD display, with three times as many pixels
across the image as normal. This mode probably won't work yet.
Only available with Freetype version 2.1.3 or newer.
- FT_RENDER_MODE_LCD_V
- Render in colour for an LCD display, with three times as many rows down
the image as normal. This mode probably won't work yet.
Only available with Freetype version 2.1.3 or newer.
- bitmap_magick([render_mode])
- A simple wrapper around the "bitmap()" method. Renders the
bitmap as normal and returns it as an Image::Magick object, which can then
be composited onto a larger bitmapped image, or manipulated using any of
the features available in Image::Magick.
The image is in the 'gray' format, with a depth of 8 bits.
The left and top distances in pixels are returned as well, in the same way
as for the "bitmap()" method.
This method, particularly the use of the left and top offsets for correct
positioning of the bitmap, is demonstrated in the magick.pl example
program.
- bitmap_pgm([render_mode])
- A simple wrapper around the "bitmap()" method. It renders the
bitmap and constructs it into a PGM (portable grey-map) image file, which
it returns as a string. The optional render-mode is passed directly
to the "bitmap()" method.
The PGM image returned is in the 'binary' format, with one byte per pixel.
It is not an efficient format, but can be read by many image manipulation
programs. For a detailed description of the format see
<http://netpbm.sourceforge.net/doc/pgm.html>
The left and top distances in pixels are returned as well, in the same way
as for the "bitmap()" method.
The render-glyph.pl example program uses this method.
- char_code()
- The character code (in Unicode) of the glyph. Could potentially return
codes in other character sets if the font doesn't have a Unicode character
mapping, but most modern fonts do.
- has_outline()
- True if the glyph has a vector outline, in which case it is safe to call
"outline_decompose()". Otherwise, the glyph only has a bitmap
image.
- height()
- The height of the glyph.
- horizontal_advance()
- The distance from the origin of this glyph to the place where the next
glyph's origin should be. Only applies to horizontal layouts. Always
positive, so for right-to-left text (such as Hebrew) it should be
subtracted from the current glyph's position.
- index()
- The glyph's index number in the font. This number is determined by the
FreeType library, and so isn't necessarily the same as any special index
number used by the font format.
- left_bearing()
- The left side bearing, which is the distance from the origin to the left
of the glyph image. Usually positive for horizontal layouts and negative
for vertical ones.
- name()
- The name of the glyph, if the font format supports glyph names, otherwise
undef.
- outline_bbox()
- The bounding box of the glyph's outline. This box will enclose all the
'ink' that would be laid down if the outline were filled in. It is
calculated by studying each segment of the outline, so may not be
particularly efficient.
The bounding box is returned as a list of four values, so the method should
be called as follows:
my ($xmin, $ymin, $xmax, $ymax) = $glyph->outline_bbox();
- outline_decompose(%callbacks)
- This method can be used to extract a description of the glyph's outline,
scaled to the face's current size. It will die if the glyph doesn't have
an outline (if it comes from a bitmap font).
Vector outlines of glyphs are represented by a sequence of operations. Each
operation can start a new curve (by moving the imaginary pen position), or
draw a line or curve from the current position of the pen to a new
position. This Perl interface will walk through the outline calling
subroutines (through code references you supply) for each operation.
Arguments are passed to your subroutines as normal, in @_.
Note: when you intend to extract the outline of a glyph, always pass the
"FT_LOAD_NO_HINTING" option when creating the face object, or
the hinting will distort the outline.
The %callbacks parameter should contain three or four
of the following keys, each with a reference to a "sub" as it's
value. The "conic_to" handler is optional, but the others are
required.
- "move_to"
- Move the pen to a new position, without adding anything to the outline.
The first operation should always be "move_to", but characters
with disconnected parts, such as "i", might have several of
these.
The x and y coordinates of the new pen position are
supplied.
- "line_to"
- Move the pen to a new position, drawing a straight line from the old
position.
The x and y coordinates of the new pen position are supplied.
Depending you how you are using this information you may have to keep
track of the previous position yourself.
- "conic_to"
- Move the pen to a new position, drawing a conic Bezier arc (also known as
a quadratic Bezier curve) from the old position, using a single control
point.
If you don't supply a "conic_to" handler, all conic curves will be
automatically translated into cubic curves.
The x and y coordinates of the new pen position are supplied,
followed by the x and y coordinates of the control
point.
- "cubic_to"
- Move the pen to a new position, drawing a cubic Bezier arc from the old
position, using two control points.
Cubic arcs are the ones produced in PostScript by the "curveto"
operator.
The x and y coordinates of the new pen position are supplied,
followed by the x and y coordinates of the first control
point, then the same for the second control point.
Note that TrueType fonts use conic curves and PostScript ones use cubic
curves.
- postscript([file-handle])
- Generate PostScript code to draw the outline of the glyph. More precisely,
the output will construct a PostScript path for the outline, which can
then be filled in or stroked as you like.
The glyph-to-eps.pl example program shows how to wrap the output in
enough extra code to generate a complete EPS file.
If you pass a file-handle to this method then it will write the PostScript
code to that file, otherwise it will return it as a string.
- right_bearing()
- The distance from the right edge of the glyph image to the place where the
origin of the next character should be (i.e., the end of the advance
width). Only applies to horizontal layouts. Usually positive.
- svg_path()
- Turn the outline of the glyph into a string in a format suitable for
including in an SVG graphics file, as the "d" attribute of a
"path" element. Note that because SVG's coordinate system has
its origin in the top left corner the outline will be upside down. An SVG
transformation can be used to flip it.
The glyph-to-svg.pl example program shows how to wrap the output in
enough XML to generate a complete SVG file, and one way of transforming
the outline to be the right way up.
If you pass a file-handle to this method then it will write the path string
to that file, otherwise it will return it as a string.
- vertical_advance()
- The distance from the origin of the current glyph to the place where the
next glyph's origin should be, moving down the page. Only applies to
vertical layouts. Always positive.
- width()
- The width of the glyph. This is the distance from the left side to the
right side, not the amount you should move along before placing the next
glyph when typesetting. For that, see the "horizontal_advance()"
method.
SEE ALSO¶
Font::FreeType, Font::FreeType::Face
AUTHOR¶
Geoff Richards <qef@laxan.com>
COPYRIGHT¶
Copyright 2004, Geoff Richards.
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.