Keyboard shortcut helpers (#2202)

* eframe web: Add WebInfo::user_agent

* Deprecate `Modifier::ALT_SHIFT`

* Add code for formatting Modifiers and Key

* Add type KeyboardShortcut

* Code cleanup

* Add Context::os/set_os to query/set what OS egui believes it is on

* Add Fonts::has_glyph(s)

* Add helper function for formatting keyboard shortcuts

* Faster code

* Add way to set a shortcut text on menu buttons

* Cleanup

* format_keyboard_shortcut -> format_shortcut

* Add TODO about supporting more keyboard sumbols

* Modifiers::plus

* Use the new keyboard shortcuts in emark editor demo

* Explain why ALT+SHIFT is a bad modifier combo

* Fix doctest

crates/epaint/src/text/font.rs

@@ -31,7 +31,7 @@ impl UvRect {
     }
 }
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub struct GlyphInfo {
     pub(crate) id: ab_glyph::GlyphId,
 
@@ -265,6 +265,12 @@ impl Font {
         slf
     }
 
+    pub fn preload_characters(&mut self, s: &str) {
+        for c in s.chars() {
+            self.glyph_info(c);
+        }
+    }
+
     pub fn preload_common_characters(&mut self) {
         // Preload the printable ASCII characters [32, 126] (which excludes control codes):
         const FIRST_ASCII: usize = 32; // 32 == space
@@ -276,7 +282,7 @@ impl Font {
         self.glyph_info(crate::text::PASSWORD_REPLACEMENT_CHAR);
     }
 
-    /// All supported characters
+    /// All supported characters.
     pub fn characters(&mut self) -> &BTreeSet<char> {
         self.characters.get_or_insert_with(|| {
             let mut characters = BTreeSet::new();
@@ -310,6 +316,16 @@ impl Font {
         self.glyph_info(c).1.advance_width
     }
 
+    /// Can we display this glyph?
+    pub fn has_glyph(&mut self, c: char) -> bool {
+        self.glyph_info(c) != self.replacement_glyph // TODO(emilk): this is a false negative if the user asks about the replacement character itself 🤦‍♂️
+    }
+
+    /// Can we display all the glyphs in this text?
+    pub fn has_glyphs(&mut self, s: &str) -> bool {
+        s.chars().all(|c| self.has_glyph(c))
+    }
+
     /// `\n` will (intentionally) show up as the replacement character.
     fn glyph_info(&mut self, c: char) -> (FontIndex, GlyphInfo) {
         if let Some(font_index_glyph_info) = self.glyph_info_cache.get(&c) {

crates/epaint/src/text/fonts.rs

@@ -430,6 +430,17 @@ impl Fonts {
         self.lock().fonts.glyph_width(font_id, c)
     }
 
+    /// Can we display this glyph?
+    #[inline]
+    pub fn has_glyph(&self, font_id: &FontId, c: char) -> bool {
+        self.lock().fonts.has_glyph(font_id, c)
+    }
+
+    /// Can we display all the glyphs in this text?
+    pub fn has_glyphs(&self, font_id: &FontId, s: &str) -> bool {
+        self.lock().fonts.has_glyphs(font_id, s)
+    }
+
     /// Height of one row of text in points
     #[inline]
     pub fn row_height(&self, font_id: &FontId) -> f32 {
@@ -627,6 +638,16 @@ impl FontsImpl {
         self.font(font_id).glyph_width(c)
     }
 
+    /// Can we display this glyph?
+    pub fn has_glyph(&mut self, font_id: &FontId, c: char) -> bool {
+        self.font(font_id).has_glyph(c)
+    }
+
+    /// Can we display all the glyphs in this text?
+    pub fn has_glyphs(&mut self, font_id: &FontId, s: &str) -> bool {
+        self.font(font_id).has_glyphs(s)
+    }
+
     /// Height of one row of text. In points
     fn row_height(&mut self, font_id: &FontId) -> f32 {
         self.font(font_id).row_height()