AG_STYLESHEET(3)

NAME
AG_StyleSheet - agar cascading style sheets

SYNOPSIS

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

DESCRIPTION
The graphical appearance of Agar widgets (including typography, colors, paddings, spacings and decorations) is determined by the stylesheet of their parent AG_Window(3).

An AG_StyleSheet defines a set of attribute blocks. Each block has a selector associated with it. Selectors allow widgets to be targeted based on their class (E), the class of their parent (E > F) or their instance names in relation to the class of their parent (E > "F").

Selector conditions allow widgets to be styled based on their current geometry ("width", "height") or the zoom level of their windows ("zoom").

Attributes defined by a stylesheet can be overridden on a per widget instance basis with the AG_SetStyle(3) family of functions.

Agar stylesheets allow C-style comments.

TYPOGRAPHY
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:

Thin
    Wt#100 Thin
ExtraLight
    Wt#200 Extra Light / Ultra Light
Light
    Wt#300 Light
Regular
    Wt#400 Regular / Normal
SemiBold
    Wt#600 Semi Bold / Demi Bold
Bold
    Wt#700 Bold
ExtraBold
    Wt#800 Extra Bold
Black
    Wt#900 Black / Heavy
!Parent
    (opposite of parent)

The font-style attribute selects the style of the font:

Italic
    Italic style (with Oblique fallback)
Oblique
    Oblique 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
SemiExpanded
    112.5% - Semi Expanded / Demi Expanded
Expanded
    125.0% - Expanded
UltraExpanded
    200.0% - Ultra Expanded
!Parent
    (opposite of parent)

COLORS
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.

PADDING AND SPACING
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.

C INTERFACE
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.

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

The following 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 */
    }

The following example uses an E > F (children of class) selector to set the color of all buttons embedded in the AG_Numerical(3) widget:

    AG_Numerical > AG_Button {
    	color: blue;
    }

The following example uses an E > "F" (children named) selector to set the color of specific button instances embedded in the AG_Numerical(3) widget:

    AG_Numerical > "increm" {
    	color: red;
    }
    AG_Numerical > "decrem" {
    	color: green;
    }

The following example switches to a condensed font when the width of the widget is below a given threshold:

    AG_HSVPal {
    	font-family: league-gothic;
    	font-size: 140%;
    }
    AG_HSVPal (width < 90) {
    	font-family: league-gothic-condensed;
    	font-size: 120%;
    }

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

SEE ALSO
AG_Intro(3), AG_Widget(3), AG_Window(3)

HISTORY
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". Agar 1.7.0 added "margin" and extended "font-weight" and "font-stretch" to include all standard weights and width variants. The selectors E > F (children of class) and E > "F" (children named) appeared in Agar 1.7.0.