Agar 1.7 Manual



#include <agar/core.h>
#include <agar/gui.h>


ScreenshotThe graphical appearance (typography, colors, paddings and spacings) of Agar widgets is produced by the Agar style compiler. Style properties can be either applied to individual widgets (with AG_SetStyle(3) calls), or defined on a per-class basis in an Agar stylesheet.

Internally, the rendering code of Agar GUI widgets will access values such as colors using a compact binary representation generated by the Agar style compiler. The style compiler runs on demand when needed (e.g., when style properties are changed or a new stylesheet is loaded).


Style attributes are case-insensitive. The following are available:
font-family The name of the font face or the exact filename of a font (e.g., "DejaVu Sans", "agar-ideograms.agbf", "foo.woff2").
font-size The font size (e.g., "80%", "10pts", "10.5pts", "12px"). Fonts of GUI elements are normally expressed in "%".
font-weight The font weight ("Thin", "ExtraLight", "Light", "Regular", "SemiBold", "Bold", "ExtraBold", "Black" or "!parent").
font-style The font style ("Normal", "Italic", "Oblique" or "!parent").
font-stretch Width variant ("Normal", "UltraCondensed", "Condensed", "SemiCondensed", "SemiExpanded", "Expanded", "UltraExpanded" or "!parent").

The font-family attribute selects the type face. Agar will look up system fonts (via fontconfig), Core Fonts as well as user-installed fonts (under AG_Config(3) AG_CONFIG_PATH_FONTS). Matching is case-insensitive except for fonts which are referenced by filename.

The font-size attribute sets the font size either in points ("10pts", "10.5pts") for vector fonts, pixels ("12px") for bitmap fonts, or in percentage of the parent widget font's size ("80%"). Generally, the font sizes of GUI elements should be given in "%" so that the zoom function may work as expected (the AG_ZoomIn(3) and AG_ZoomOut(3) functions work by simply increasing or decreasing the target window's "font-size").

The font-weight attribute sets the weight of the font:
ThinWt#100 Thin
ExtraLightWt#200 Extra Light / Ultra Light
LightWt#300 Light
RegularWt#400 Regular / Normal
SemiBoldWt#600 Semi Bold / Demi Bold
BoldWt#700 Bold
ExtraBoldWt#800 Extra Bold
BlackWt#900 Black / Heavy
!Parent(opposite of parent)

The font-style attribute selects the style of the font:
ItalicItalic style (with Oblique fallback)
ObliqueOblique style (with Italic fallback)
!Parent(opposite of parent)

The font-stretch attribute selects the width variant:
UltraCondensed 50.0% - Ultra Condensed
Condensed 75.0% - Condensed
SemiCondensed 87.5% - Semi Condensed / Demi Condensed
SemiExpanded112.5% - Semi Expanded / Demi Expanded
Expanded125.0% - Expanded
UltraExpanded200.0% - Ultra Expanded
!Parent(opposite of parent)


Color-defining style attributes include:
color Foreground primary
background-color Background primary
text-color Text and vector icons
line-color Lines and filled shapes
high-color Shading (top and left)
low-color Shading (bottom and right)
selection-color Selection primary

Colors allow an optional state selector (e.g., "color#focused"). If no selector is given then the given color is assigned to all states.
"#unfocused"Widget is not focused (default state).
"#focused"Widget is focused (see AG_WidgetFocus(3)).
"#disabled"Widget is disabled (see AG_WidgetDisable(3)).
"#hover"Cursor is over the widget (MOUSEOVER is set).

Color values can be specified using any one of the representations below. See AG_ColorFromString(3) for details.
"8-bit Device RGB""r,g,b[,a]" or "rgb(r,g,b[,a])"
"16-bit Device RGB""rgb16(r,g,b[,a])"
"Hue, Saturation and Value""hsv(h,s,v[,a])"
"16-bit hex""#rgb[a]"
"32-bit hex""#rrggbb[aa]"
"64-bit hex""#rrrrggggbbbb[aaaa]"
"Color keyword""AliceBlue", "antiquewhite"

RGBA and HSV components may be expressed in "%" (in relation to the same color entry in the parent widget's palette).

Color keywords are matched case-insensitively.


Paddings, margins and inner spacings are specified in pixels:
padding "<Number>", "<T> <R> <B> <L>" or "inherit"
margin "<Number>", "<T> <R> <B> <L>" or "inherit"
spacing "<Number>", "<H> <V>" or "inherit"

The padding attribute sets the inner padding amount in pixels. If given as a single "<Number>", the same amount is applied to all sides. Negative values are allowed, and may be used to condense content.

The margin attribute sets the outer margin amount in pixels. If given as a single "<Number>", the same amount is applied to all sides. The margin amounts must be positive.

The spacing attribute sets the horizontal and vertical spacings between inner elements of a widget. If given as a single "<Number>", the same amount is used for both horizontal and vertical spacings. Negative values are allowed, and may be used to condense content.

Margin is handled generically by container widgts. Padding and inner spacings are implemented in a widget-specific way. Different widget classes will handle padding and spacing differently.


void AG_InitStyleSheet (AG_StyleSheet *ss)

void AG_DestroyStyleSheet (AG_StyleSheet *css)

AG_StyleSheet * AG_LoadStyleSheet (void *obj, const char *path)

int AG_LookupStyleSheet (AG_StyleSheet *css, void *widget, const char *key, char **rv)

The AG_InitStyleSheet() function initializes the given AG_StyleSheet as an empty style sheet. AG_DestroyStyleSheet() releases all resources allocated by a style sheet.

The AG_LoadStyleSheet() function loads a style sheet from path. On success, a newly allocated AG_StyleSheet is returned. If path begins with a "_" character, AG_LoadStyleSheet() will search for a statically-compiled stylesheet (i.e., "_agStyleDefault" is always available).

The AG_LookupStyleSheet() routine searches the style sheet for the specified attribute (identified by key). If the style sheet defines an attribute applicable to the specified widget instance (the widget argument), its value is returned into rv.


Agar's default stylesheet is compiled from gui/style.css. It is a good starting point for writing new stylesheets.

The stylesheet fragment selects a condensed font, tweaks the color scheme and sets padding values for the AG_Button(3) class:
AG_Button {
	font-family: league-gothic;
	font-stretch: condensed;
	font-size: 120%;

	color: AntiqueWhite;
	text-color: #000;

	color#disabled: rgb(200,200,200);
	text-color#disabled: rgb(125,125,125);

	high-color#hover: red;
	low-color#hover: darkred;

	padding: 5 4 5 4;      /* TRBL */

By default, a widget instance inherits its style attributes from its parent. The syntax allows certain attributes, such as "font-size" and "color" to be specified in relation to the parent. For example:
font-size: 50%;			# Half of parent font size
color: hsv(100%,50%,100%);	# Half of parent saturation
color: hsv(100%,100%,75%);	# 3/4 of parent value


AG_Intro(3), AG_Widget(3), AG_Window(3)


A very basic AG_StyleSheet language first appeared in Agar 1.5.0. Agar 1.6.0 improved parsing and validation, introduced a new color scheme, added typography features as well as "padding" and "spacing". ElectronTubeStore is © 2022 Julien Nadeau Carriere <>.
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