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This manual documents MIT/GNU Scheme Pucked Pango 0.13.
Copyright © 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 Matthew Birkholz
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”
| • Introduction: | ||
| • API Reference: | ||
| • GNU Free Documentation License: |
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The Pango system is a collection of Scheme data types and procedures providing a Schemely interface to the Pango text layout library. Very little of the library’s API has been wrapped — just what is listed herein. As one might expect of a “Schemely” interface, all toolkit resources are protected from “leaking” by the garbage collector. When Scheme’s representative of a toolkit resource is dropped and collected, the toolkit resource is freed, just as the C/Unix FFI’s malloced aliens are automatically freed.
The Pango library is built “on top” of GLib, which is not ready for
multiple threads. To ensure that just one Scheme thread is “in” the
toolkits, the with-glib-lock procedure should be used, else
every callout will write a warning line to stderr.
See with-glib-lock in GLib Plugin Manual.
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All of the Pango system’s public bindings can be found in the
(pango) package and are described here.
PangoLayouts are GObjects and so are represented by instances of a new
subclass of <gobject>: <pango-layout>s. Other Pango
objects are represented by simple aliens. In either case when a
plugin procedure returns an object that must be freed, it arranges to
do so automatically, after the representative is garbage collected.
A direct subclass of gobject representing a reference to a PangoLayout.
Type guarantor.
The layout’s context, a PangoContext alien.
Re-lays-out layout according to the (new) state of its context.
Layout’s font description, a PangoFontDescription alien, or a null alien if the font description is set in layout’s context. The description is owned by the layout and must not be modified nor freed.
Sets layout’s default font to font, a PangoFontDescription alien.
Sets layout’s text to string. The new text will be laid out, possibly changing layout’s dimensions.
Sets layout’s text to markup, a simplified XML string.
Markup is XML with the following simplifications.
The markup format does support:
& < > " '
Valid elements are:
bBold
bigMakes font relatively larger, equivalent to <span size="larger">.
iItalic
sStrikethrough
subSubscript
supSuperscript
smallMakes font relatively smaller. Equivalent to <span size="smaller">.
ttMonospace font
uUnderline
spanGeneral form with many attributes listed below.
Valid attributes for the span element are:
font, font_descA font description string acceptable to
pango-font-description-from-string (e.g. Sans Italic
12). Note that any other span attributes will override this
description. If you have font="Sans Italic" and also
style="normal", you will get Sans normal, not italic.
font_family, faceA font family name.
font_size, sizeFont size in 1024ths of a point, or one of the absolute sizes
xx-small, x-small, small, medium,
large, x-large, xx-large, or one of the relative
sizes smaller or larger. If you want to specify a
absolute size, it is usually easier to take advantage of the ability
to specify a partial font description using font; you can use
font="12.5" rather than size="12800".
font_style, styleOne of normal, oblique, italic.
font_weight, weightOne of ultralight, light, normal, bold,
ultrabold, heavy, or a numeric weight.
font_variant, variantOne of normal or smallcaps.
font_stretch, stretchOne of ultracondensed, extracondensed, condensed,
semicondensed, normal, semiexpanded,
expanded, extraexpanded, ultraexpanded.
foreground, fgcolor, colorAn RGB color specification such as #00FF00 or a color name such
as red.
background, bgcolorAn RGB color specification such as #00FF00 or a color name such
as red.
underlineOne of none, single, double, low,
error.
underline_colorThe color of underlines; an RGB color specification such as
#00FF00 or a color name such as red.
riseVertical displacement, in 10000ths of an em. Can be negative for subscript, positive for superscript.
strikethroughtrue or false whether to strike through the text.
strikethrough_colorThe color of strikethrough lines; an RGB color specification such as
#00FF00 or a color name such as red
fallbackTrue or false whether to enable fallback. If disabled,
then characters will only be used from the closest matching font on
the system. No fallback will be done to other fonts on the system that
might contain the characters in the text. Fallback is enabled by
default. Most applications should not disable fallback.
langA language code (e.g. en for english), indicating the text
language.
letter_spacingInter-letter spacing in 1024ths of a point.
gravityOne of south, east, north, west, auto.
gravity_hintOne of natural, strong, line.
The y position (in pixels, not pangos) of the baseline of the first line in layout.
Applies receiver to layout’s width and height.
Applies receiver to the x and y coordinates (relative to the upper-left corner of layout) and the width and height of the character at index.
Returns the byte index of the character at position (x, y)
within layout. X and y should be given in pixels
relative to the top left of the layout. Returns #f if x
or y are not inside layout.
A new PangoFontDescription alien. If it is garbage collected, the
toolkit object will be freed with pango-font-description-free.
String can have three whitespace separated parts:
family-list style-options size.
Family-list can be a comma separated list of families optionally
terminated by a comma.
Style-options can be a whitespace separated list of
words where each word describes one of style, variant, weight,
stretch, or gravity.
Size can be a decimal number (size in points) or an absolute
size followed by the unit modifier px.
Any one of these parts may be absent. If family-list is absent,
then the family name field of the resulting font description will be
empty. If style-options is missing, then all style options
will be set to default values. If size is missing, the size in
the resulting font description will be set to 0.
A string that would parse as font, a PangoFontDescription alien.
A copy of font, a new PangoFontDescription alien.
Frees font, an alien PangoFontDescription.
The PangoFontDescription alien owned by context, an alien PangoContext.
Sets context’s PangoFontDescription to a copy of font.
A new PangoFontMetrics alien to which Scheme holds a reference. If
the alien is garbage collected, the reference will be released with
pango_font_metric_unref.
The space between lines in any up-to-date pango layout using context.
The ascent of metrics, a PangoFontMetrics alien. This is the distance from the baseline to the highest point of the glyphs of the font. This is positive in practically all fonts.
The descent of metrics, a PangoFontMetrics alien. This is the distance from the baseline to the lowest point of the glyphs of the font. This is positive in practically all fonts.
The approximate character width of metrics, a PangoFontMetrics alien. This is merely a representative value useful, for example, for determining the initial size for a window. The actual glyphs will be wider and narrower than this.
Releases Scheme’s reference to metrics with
pango_font_metric_unref. All operations on metrics will
thereafter signal an error.
Parses string and returns a floating-vector containing four flonums between 0. and 1. inclusive: the red, green, blue and alpha components. String should be in one of the following formats.
Returns a color, else signals error:wrong-type-argument with
operator. Object should be a color, symbol or string.
Symbols and strings are converted to colors by
pango-color-parse.
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