Improve docs concerning custom fonts, themes and accessibility

Closes https://github.com/emilk/egui/pull/370
Closes https://github.com/emilk/egui/issues/372

README.md

@@ -10,7 +10,7 @@
 
 egui is a simple, fast, and highly portable immediate mode GUI library for Rust. egui runs on the web, natively, and [in your favorite game engine](#integrations) (or will soon).
 
-egui aims to be the easiest-to-use Rust GUI libary, and the simplest way to make a web app in Rust.
+egui aims to be the easiest-to-use Rust GUI library, and the simplest way to make a web app in Rust.
 
 egui can be used anywhere you can draw textured triangles, which means you can easily integrate it into your game engine of choice.
 
@@ -68,7 +68,7 @@ ui.label(format!("Hello '{}', age {}", name, age));
 
 ## Goals
 
-* The easiest to use GUI libary
+* The easiest to use GUI library
 * Responsive: target 60 Hz in debug build
 * Friendly: difficult to make mistakes, and shouldn't panic
 * Portable: the same code works on the web and as a native app
@@ -79,7 +79,7 @@ ui.label(format!("Hello '{}', age {}", name, age));
 * Extensible: [easy to write your own widgets for egui](https://github.com/emilk/egui/blob/master/egui_demo_lib/src/apps/demo/toggle_switch.rs)
 * Modular: You should be able to use small parts of egui and combine them in new ways
 * Safe: there is no `unsafe` code in egui
-* Minimal dependencies: [`ahash`](https://crates.io/crates/ahash) [`atomic_refcell`](https://crates.io/crates/atomic_refcell) [`ordered-float`](https://crates.io/crates/) [`rusttype`](https://crates.io/crates/rusttype).
+* Minimal dependencies: [`ahash`](https://crates.io/crates/ahash) [`atomic_refcell`](https://crates.io/crates/atomic_refcell) [`ordered-float`](https://crates.io/crates/ordered-float) [`rusttype`](https://crates.io/crates/rusttype).
 
 egui is *not* a framework. egui is a library you call into, not an environment you program for.
 
@@ -87,7 +87,7 @@ egui is *not* a framework. egui is a library you call into, not an environment y
 
 ### Non-goals
 
-* Become the most powerful GUI libary
+* Become the most powerful GUI library
 * Native looking interface
 * Advanced and flexible layouts (that's fundamentally incompatible with immediate mode)
 
@@ -134,7 +134,11 @@ egui is in active development. It works well for what it does, but it lacks many
 * Tooltips on hover
 * More
 
-<img src="media/widget_gallery_0.8.0.gif" width="50%">
+<img src="media/widget_gallery.gif" width="50%">
+
+Light Theme:
+
+<img src="media/light_theme.png" width="50%">
 
 ## How it works
 
@@ -234,7 +238,7 @@ The short of it is this: immediate mode GUI libraries are easier to use, but les
 The main advantage of immediate mode is that the application code becomes vastly simpler:
 
 * You never need to have any on-click handlers and callbacks that disrupts your code flow.
-* You don't have to worry about a linger callback calling something that is gone.
+* You don't have to worry about a lingering callback calling something that is gone.
 * Your GUI code can easily live in a simple function (no need for an object just for the UI).
 * You don't have to worry about app state and GUI state being out-of-sync (i.e. the GUI showing something outdated), because the GUI isn't storing any state - it is showing the latest state *immediately*.
 
@@ -275,6 +279,17 @@ Overall, ID handling is a rare inconvenience, and not a big disadvantage.
 
 Also see [GitHub Discussions](https://github.com/emilk/egui/discussions/categories/q-a).
 
+### Can I use `egui` with non-latin characters?
+Yes! But you need to install your own font (`.ttf` or `.otf`) using `Context::set_fonts`.
+
+### Can I customize the look of egui?
+Yes! You can customize the colors, spacing and sizes of everything. By default egui comes with a dark and a light theme.
+
+### What about accessibility, such as screen readers?
+There is experimental support for a screen reader. In [the web demo](https://emilk.github.io/egui/index.html) you can enable it in the "Backend" tab.
+
+Read more at <https://github.com/emilk/egui/issues/167>.
+
 ### What is the difference between egui and eframe?
 
 `egui` is a 2D user interface library for laying out and interacting with buttons, sliders, etc.

egui/src/context.rs

@@ -415,7 +415,12 @@ impl Context {
         self.fonts().texture()
     }
 
-    /// Will become active at the start of the next frame.
+    /// Tell `egui` which fonts to use.
+    ///
+    /// The default `egui` fonts only support latin and cyrillic alphabets,
+    /// but you can call this to install additional fonts that support e.g. korean characters.
+    ///
+    /// The new fonts will become active at the start of the next frame.
     pub fn set_fonts(&self, font_definitions: FontDefinitions) {
         if let Some(current_fonts) = &self.fonts {
             // NOTE: this comparison is expensive since it checks TTF data for equality
@@ -434,6 +439,8 @@ impl Context {
 
     /// The [`Style`] used by all new windows, panels etc.
     ///
+    /// You can also use [`Ui::style_mut`] to change the style of a single [`Ui`].
+    ///
     /// Example:
     /// ```
     /// # let mut ctx = egui::CtxRef::default();

egui/src/data/input.rs

@@ -6,6 +6,9 @@ use crate::emath::*;
 ///
 /// Set the values that make sense, leave the rest at their `Default::default()`.
 ///
+/// You can check if `egui` is using the inputs using
+/// [`crate::Context::wants_pointer_input`] and [`crate::Context::wants_keyboard_input`].
+///
 /// All coordinates are in points (logical pixels) with origin (0, 0) in the top left corner.
 #[derive(Clone, Debug)]
 pub struct RawInput {

egui/src/input_state.rs

@@ -14,6 +14,9 @@ const MAX_CLICK_DIST: f32 = 6.0; // TODO: move to settings
 const MAX_CLICK_DELAY: f64 = 0.3; // TODO: move to settings
 
 /// Input state that egui updates each frame.
+///
+/// You can check if `egui` is using the inputs using
+/// [`crate::Context::wants_pointer_input`] and [`crate::Context::wants_keyboard_input`].
 #[derive(Clone, Debug)]
 pub struct InputState {
     /// The raw input we got this frame from the backend.

egui/src/style.rs

@@ -5,7 +5,12 @@
 use crate::{color::*, emath::*, Response};
 use epaint::{Shadow, Stroke, TextStyle};
 
-/// Specifies the look and feel of a [`Ui`].
+/// Specifies the look and feel of egui.
+///
+/// You can change the visuals of a [`Ui`] with [`Ui::style_mut`]
+/// and of everything with [`crate::Context::set_style`].
+///
+/// If you want to change fonts, use [`crate::Context::set_fonts`] instead.
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "persistence", serde(default))]
@@ -22,11 +27,16 @@ pub struct Style {
     /// * `Some(false)`: default off
     pub wrap: Option<bool>,
 
+    /// Sizes and distances between widgets
     pub spacing: Spacing,
+
+    /// How and when interaction happens.
     pub interaction: Interaction,
+
+    /// Colors etc.
     pub visuals: Visuals,
 
-    /// How many seconds a typical animation should last
+    /// How many seconds a typical animation should last.
     pub animation_time: f32,
 
     /// Options to help debug why egui behaves strangely.
@@ -58,6 +68,7 @@ impl Style {
     }
 }
 
+/// Controls the sizes and distances between widgets.
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "persistence", serde(default))]
@@ -119,6 +130,7 @@ impl Spacing {
     }
 }
 
+/// How and when interaction happens.
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "persistence", serde(default))]
@@ -133,6 +145,12 @@ pub struct Interaction {
     pub show_tooltips_only_when_still: bool,
 }
 
+/// Controls the visual style (colors etc) of egui.
+///
+/// You can change the visuals of a [`Ui`] with [`Ui::visuals_mut`]
+/// and of everything with [`crate::Context::set_visuals`].
+///
+/// If you want to change fonts, use [`crate::Context::set_fonts`] instead.
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "persistence", serde(default))]
@@ -224,6 +242,7 @@ pub struct Selection {
     pub stroke: Stroke,
 }
 
+/// The visuals of widgets for different states of interaction.
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "persistence", serde(default))]

egui/src/ui.rs

@@ -769,7 +769,26 @@ impl Ui {
         InnerResponse::new(ret, response)
     }
 
-    /// Convenience function to get a region to paint on
+    /// Convenience function to get a region to paint on.
+    ///
+    /// Note that egui uses screen coordinates for everything.
+    ///
+    /// ```
+    /// # use egui::*;
+    /// # let mut ui = &mut egui::Ui::__test();
+    /// # use std::f32::consts::TAU;
+    /// let size = Vec2::splat(16.0);
+    /// let (response, painter) = ui.allocate_painter(size, Sense::hover());
+    /// let rect = response.rect;
+    /// let c = rect.center();
+    /// let r = rect.width() / 2.0 - 1.0;
+    /// let color = Color32::from_gray(128);
+    /// let stroke = Stroke::new(1.0, color);
+    /// painter.circle_stroke(c, r, stroke);
+    /// painter.line_segment([c - vec2(0.0, r), c + vec2(0.0, r)], stroke);
+    /// painter.line_segment([c, c + r * Vec2::angled(TAU * 1.0 / 8.0)], stroke);
+    /// painter.line_segment([c, c + r * Vec2::angled(TAU * 3.0 / 8.0)], stroke);
+    /// ```
     pub fn allocate_painter(&mut self, desired_size: Vec2, sense: Sense) -> (Response, Painter) {
         let response = self.allocate_response(desired_size, sense);
         let clip_rect = self.clip_rect().intersect(response.rect); // Make sure we don't paint out of bounds

egui_demo_lib/src/apps/demo/font_book.rs

@@ -58,11 +58,24 @@ impl super::View for FontBook {
         use super::font_contents_ubuntu::UBUNTU_FONT_CHARACTERS;
 
         ui.label(format!(
-            "egui supports {} standard characters and {} emojis.\nClick on a character to copy it.",
+            "The default egui fonts supports {} standard characters and {} emojis.",
             UBUNTU_FONT_CHARACTERS.len(),
             FULL_EMOJI_LIST.len(),
         ));
 
+        ui.horizontal_wrapped(|ui| {
+            ui.spacing_mut().item_spacing.x = 0.0;
+            ui.label("You can add more characters by installing additional fonts with ");
+            ui.add(
+                egui::Hyperlink::from_label_and_url(
+                    "Context::set_fonts",
+                    "https://docs.rs/egui/latest/egui/struct.Context.html#method.set_fonts",
+                )
+                .text_style(egui::TextStyle::Monospace),
+            );
+            ui.label(".");
+        });
+
         ui.separator();
 
         egui::ComboBox::from_label("Text style")

egui_demo_lib/src/apps/demo/misc_demo_window.rs

@@ -88,8 +88,9 @@ impl View for MiscDemoWindow {
                 ui.horizontal(|ui| {
                     ui.label("You can pretty easily paint your own small icons:");
                     use std::f32::consts::TAU;
-                    let (rect, _response) = ui.allocate_at_least(Vec2::splat(16.0), Sense::hover());
+                    let size = Vec2::splat(16.0);
-                    let painter = ui.painter();
+                    let (response, painter) = ui.allocate_painter(size, Sense::hover());
+                    let rect = response.rect;
                     let c = rect.center();
                     let r = rect.width() / 2.0 - 1.0;
                     let color = Color32::from_gray(128);

epaint/src/text/fonts.rs

@@ -74,11 +74,42 @@ fn rusttype_font_from_font_data(name: &str, data: &FontData) -> rusttype::Font<'
 /// Often you would start with [`FontDefinitions::default()`] and then add/change the contents.
 ///
 /// ```
-/// let mut fonts = epaint::text::FontDefinitions::default();
+/// # use {epaint::text::{FontDefinitions, TextStyle, FontFamily}};
+/// # struct FakeEguiCtx {};
+/// # impl FakeEguiCtx { fn set_fonts(&self, _: FontDefinitions) {} }
+/// # let ctx = FakeEguiCtx {};
+/// let mut fonts = FontDefinitions::default();
+///
 /// // Large button text:
 /// fonts.family_and_size.insert(
-///     epaint::text::TextStyle::Button,
+///     TextStyle::Button,
-///     (epaint::text::FontFamily::Proportional, 32.0));
+///     (FontFamily::Proportional, 32.0)
+/// );
+///
+/// ctx.set_fonts(fonts);
+/// ```
+///
+/// You can also install your own custom fonts:
+/// ```
+/// # use {epaint::text::{FontDefinitions, TextStyle, FontFamily}};
+/// # struct FakeEguiCtx {};
+/// # impl FakeEguiCtx { fn set_fonts(&self, _: FontDefinitions) {} }
+/// # let ctx = FakeEguiCtx {};
+/// let mut fonts = FontDefinitions::default();
+///
+/// // Install my own font (maybe supporting non-latin characters):
+/// fonts.font_data.insert("my_font".to_owned(),
+///    std::borrow::Cow::Borrowed(include_bytes!("../../fonts/Ubuntu-Light.ttf"))); // .ttf and .otf supported
+///
+/// // Put my font first (highest priority):
+/// fonts.fonts_for_family.get_mut(&FontFamily::Proportional).unwrap()
+///     .insert(0, "my_font".to_owned());
+///
+/// // Put my font as last fallback for monospace:
+/// fonts.fonts_for_family.get_mut(&FontFamily::Monospace).unwrap()
+///     .push("my_font".to_owned());
+///
+/// ctx.set_fonts(fonts);
 /// ```
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]