Context::add_font

crates/egui/src/context.rs

@@ -9,7 +9,7 @@ use epaint::{
     pos2,
     stats::PaintStats,
     tessellator,
-    text::Fonts,
+    text::{FontInsert, Fonts},
     util::OrderedFloat,
     vec2, ClippedPrimitive, ClippedShape, Color32, ImageData, ImageDelta, Pos2, Rect,
     TessellationOptions, TextureAtlas, TextureId, Vec2,
@@ -582,6 +582,29 @@ impl ContextImpl {
             log::trace!("Loading new font definitions");
         }
 
+        if !self.memory.add_fonts.is_empty() {
+            let fonts = self.memory.add_fonts.drain(..);
+            for font in fonts {
+                self.fonts.clear();
+                self.font_definitions
+                    .font_data
+                    .insert(font.name.clone(), font.data);
+                let fam = self
+                    .font_definitions
+                    .families
+                    .entry(font.family)
+                    .or_default();
+                if font.family_append {
+                    fam.push(font.name);
+                } else {
+                    fam.insert(0, font.name);
+                };
+            }
+
+            #[cfg(feature = "log")]
+            log::trace!("Loading new font definitions");
+        }
+
         let mut is_new = false;
 
         let fonts = self
@@ -1727,6 +1750,7 @@ impl Context {
     /// 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 pass.
+    /// This will overwrite the existing fonts
     pub fn set_fonts(&self, font_definitions: FontDefinitions) {
         crate::profile_function!();
 
@@ -1748,6 +1772,39 @@ impl Context {
         }
     }
 
+    /// 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 font will become active at the start of the next pass.
+    /// This will keep the existing fonts
+    pub fn add_font(&self, new_font: FontInsert) {
+        crate::profile_function!();
+
+        let pixels_per_point = self.pixels_per_point();
+
+        let mut update_fonts = true;
+
+        self.read(|ctx| {
+            if let Some(current_fonts) = ctx.fonts.get(&pixels_per_point.into()) {
+                if current_fonts
+                    .lock()
+                    .fonts
+                    .definitions()
+                    .font_data
+                    .contains_key(&new_font.name)
+                {
+                    update_fonts = false; // no need to update
+                }
+            }
+        });
+
+        if update_fonts {
+            self.memory_mut(|mem| mem.add_fonts.push(new_font));
+        }
+    }
+
     /// Does the OS use dark or light mode?
     /// This is used when the theme preference is set to [`crate::ThemePreference::System`].
     pub fn system_theme(&self) -> Option<Theme> {

crates/egui/src/memory/mod.rs

@@ -79,6 +79,10 @@ pub struct Memory {
     #[cfg_attr(feature = "persistence", serde(skip))]
     pub(crate) new_font_definitions: Option<epaint::text::FontDefinitions>,
 
+    /// add new font that will be applied at the start of the next frame
+    #[cfg_attr(feature = "persistence", serde(skip))]
+    pub(crate) add_fonts: Vec<epaint::text::FontInsert>,
+
     // Current active viewport
     #[cfg_attr(feature = "persistence", serde(skip))]
     pub(crate) viewport_id: ViewportId,
@@ -119,6 +123,7 @@ impl Default for Memory {
             layer_transforms: Default::default(),
             popup: Default::default(),
             everything_is_visible: Default::default(),
+            add_fonts: Default::default(),
         };
         slf.interactions.entry(slf.viewport_id).or_default();
         slf.areas.entry(slf.viewport_id).or_default();

crates/epaint/src/text/fonts.rs

@@ -254,6 +254,34 @@ pub struct FontDefinitions {
     pub families: BTreeMap<FontFamily, Vec<String>>,
 }
 
+#[derive(Debug, Clone)]
+pub struct FontInsert {
+    /// Font name
+    pub name: String,
+
+    /// A `.ttf` or `.otf` file and a font face index.
+    pub data: FontData,
+
+    /// Sets the font family
+    pub family: FontFamily,
+
+    /// If append is true & there are multiple fonts for that font family the font will be added as fallback.
+    /// This decides if the font is added to the front or the back.
+    /// So the first font is the primary, and then comes a list of fallbacks in order of priority.
+    pub family_append: bool,
+}
+
+impl FontInsert {
+    pub fn new(name: &str, data: FontData, family: FontFamily, primary_font: bool) -> Self {
+        Self {
+            name: name.to_owned(),
+            data,
+            family,
+            family_append: !primary_font,
+        }
+    }
+}
+
 impl Default for FontDefinitions {
     /// Specifies the default fonts if the feature `default_fonts` is enabled,
     /// otherwise this is the same as [`Self::empty`].

crates/epaint/src/text/mod.rs

@@ -10,7 +10,9 @@ mod text_layout_types;
 pub const TAB_SIZE: usize = 4;
 
 pub use {
-    fonts::{FontData, FontDefinitions, FontFamily, FontId, FontTweak, Fonts, FontsImpl},
+    fonts::{
+        FontData, FontDefinitions, FontFamily, FontId, FontInsert, FontTweak, Fonts, FontsImpl,
+    },
     text_layout::layout,
     text_layout_types::*,
 };