Theming

The core defines no look of its own. Every color, metric and tuning number that GuiTheme holds comes from the application, which defines one function:

// source/theme.cpp
#include "libgui/GuiTheme.h"
 
void GuiThemeInit(GuiTheme& t)
{
    t.background = { 18, 22, 29, 255 };
    t.accent     = { 255, 150, 40, 255 };
    // ... every other field
}

GuiThemeInit() is declared by GuiTheme.h and defined by the application, like main(). A program that does not define it fails to link, so a forgotten theme can never show up as an invisible UI. It runs once, the first time anything calls GuiTheme::current(), and must not call GuiTheme::current() itself. A GuiTheme made any other way (GuiTheme t;) has every field zero.

source/theme.cpp is the template's theme. Copy it and change the values to restyle an application; the library files under source/libgui/ do not change.

What is in a theme

Group	Fields	Used by
Colors	background, surface, surfaceRaised, outline, outlineStrong, accent, accentLight, accentDark, text, textMuted, textOnAccent, textInverse, good, highlight, mark, shadow	the style recipes, widgets, glyphs
Metrics	radius, strokeWidth, padding, spacing, shadowBlur	cards, panels, layouts
Glyphs	glyphSize, glyphBumperWidth, glyphBumperHeight, glyphFontSize, glyphFontSizeSmall	GuiGlyph
Recipe tuning	shadowOffsetY, glowGrow, focusGlowAlpha, pressGlowAlpha, buttonGlowBlur, buttonGlowAlpha, rowPressAlpha, cardDisabledAlpha, buttonDisabledAlpha, buttonStrokeLight, barDarken	cardStyle(), buttonStyle(), rowStyle(), barStyle()

Colors that depend on each other are the application's choice, not the library's: the template sets highlight to a mix of surfaceRaised and outlineStrong, which is one line in GuiThemeInit(). textInverse is the ink on a badge filled with text (the letter or symbol on a glyph), so it reads on text the way textOnAccent reads on accent.

The recipes

panelStyle(), cardStyle(), buttonStyle(), chipStyle(), rowStyle() and barStyle() build a GuiShapeStyle from the theme. They decide structure (which color goes at which end of a gradient, which states glow) and take every number from the fields above. An application that wants a look the recipes do not give builds its own GuiShapeStyle and passes it with .style(...); it can still read colors from GuiTheme::current().