Add option to set label fonts

Closes linebender#774

druid/examples/styled_text.rs

@@ -14,7 +14,7 @@
 
 //! Example of dynamic text styling
 
-use druid::widget::{Flex, Label, MainAxisAlignment, Painter, Parse, Stepper, TextBox};
+use druid::widget::{Checkbox, Flex, Label, MainAxisAlignment, Painter, Parse, Stepper, TextBox};
 use druid::{
     theme, AppLauncher, Color, Data, Key, Lens, LensExt, LensWrap, LocalizedString, PlatformError,
     RenderContext, Widget, WidgetExt, WindowDesc,
@@ -27,6 +27,7 @@ const MY_CUSTOM_TEXT_SIZE: Key<f64> = Key::new("styled_text.custom_text_size");
 struct AppData {
     text: String,
     size: f64,
+    mono: bool,
 }
 fn main() -> Result<(), PlatformError> {
     let main_window = WindowDesc::new(ui_builder).title(
@@ -35,6 +36,7 @@ fn main() -> Result<(), PlatformError> {
     let data = AppData {
         text: "Here's some sample text".to_string(),
         size: 24.0,
+        mono: false,
     };
 
     AppLauncher::with_window(main_window)
@@ -57,26 +59,39 @@ fn ui_builder() -> impl Widget<AppData> {
     });
 
     // This is druid's default text style.
-    // It's set by theme::LABEL_COLOR and theme::TEXT_SIZE_NORMAL
+    // It's set by theme::LABEL_COLOR, theme::TEXT_SIZE_NORMAL, and theme::FONT_NAME
     let label =
         Label::new(|data: &String, _env: &_| format!("Default: {}", data)).lens(AppData::text);
 
-    // The text_color and text_size builder methods can override the defaults
-    // provided by the theme by passing in a Key or a concrete value.
+    // The text_color, text_size, and font builder methods can override the
+    // defaults provided by the theme by passing in a Key or a concrete value.
     //
-    // In this example, text_color receives a Key from the theme, while
-    // text_size gets a custom key which we set with the env_scope wrapper.
-    let styled_label =
-        Label::new(|data: &AppData, _env: &_| format!("Size {:.1}: {}", data.size, data.text))
-            .with_text_color(theme::PRIMARY_LIGHT)
-            .with_text_size(MY_CUSTOM_TEXT_SIZE)
-            .background(my_painter)
-            .on_click(|_, data, _| {
-                data.size *= 1.1;
-            })
-            .env_scope(|env: &mut druid::Env, data: &AppData| {
-                env.set(MY_CUSTOM_TEXT_SIZE, data.size);
-            });
+    // In this example, text_color receives a Key from the theme, text_size
+    // gets a custom key which we set with the env_scope wrapper, and the
+    // default font key (theme::FONT_NAME) is overridden in the env_scope
+    // wrapper. (Like text_color and text_size, the font can be set using the
+    // with_font builder method, but overriding here makes it easy to fall back
+    // to the default font)
+    let styled_label = Label::new(|data: &AppData, _env: &_| {
+        format!(
+            "Size {:.1}{}: {}",
+            data.size,
+            if data.mono { " mono" } else { "" },
+            data.text
+        )
+    })
+    .with_text_color(theme::PRIMARY_LIGHT)
+    .with_text_size(MY_CUSTOM_TEXT_SIZE)
+    .background(my_painter)
+    .on_click(|_, data, _| {
+        data.size *= 1.1;
+    })
+    .env_scope(|env: &mut druid::Env, data: &AppData| {
+        env.set(MY_CUSTOM_TEXT_SIZE, data.size);
+        if data.mono {
+            env.set(theme::FONT_NAME, "monospace");
+        }
+    });
 
     let stepper = Stepper::new()
         .with_range(0.0, 100.0)
@@ -91,6 +106,8 @@ fn ui_builder() -> impl Widget<AppData> {
 
     let stepper_row = Flex::row().with_child(stepper_textbox).with_child(stepper);
 
+    let mono_checkbox = Checkbox::new("Monospace").lens(AppData::mono);
+
     let input = TextBox::new().fix_width(200.0).lens(AppData::text);
 
     Flex::column()
@@ -101,5 +118,7 @@ fn ui_builder() -> impl Widget<AppData> {
         .with_spacer(32.0)
         .with_child(stepper_row)
         .with_spacer(8.0)
+        .with_child(mono_checkbox)
+        .with_spacer(8.0)
         .with_child(input.padding(5.0))
 }

druid/src/env.rs

@@ -420,6 +420,12 @@ macro_rules! impl_value_type_borrowed {
                 Value::$var(self)
             }
         }
+
+        impl Into<Value> for &$ty {
+            fn into(self) -> Value {
+                Value::$var(self.to_owned())
+            }
+        }
     };
 }
 

druid/src/widget/label.rs

@@ -53,6 +53,7 @@ pub struct Label<T> {
     text: LabelText<T>,
     color: KeyOrValue<Color>,
     size: KeyOrValue<f64>,
+    font: KeyOrValue<&'static str>,
 }
 
 impl<T: Data> Label<T> {
@@ -78,6 +79,7 @@ impl<T: Data> Label<T> {
             text,
             color: theme::LABEL_COLOR.into(),
             size: theme::TEXT_SIZE_NORMAL.into(),
+            font: theme::FONT_NAME.into(),
         }
     }
 
@@ -132,6 +134,16 @@ impl<T: Data> Label<T> {
         self
     }
 
+    /// Builder-style method for setting the font.
+    ///
+    /// The argument can be either a `&'static str` or a [`Key<&'static str>`].
+    ///
+    /// [`Key<&str>`]: struct.Key.html
+    pub fn with_font(mut self, font: impl Into<KeyOrValue<&'static str>>) -> Self {
+        self.font = font.into();
+        self
+    }
+
     /// Set a new text.
     ///
     /// Takes an already resolved string as input.
@@ -163,8 +175,17 @@ impl<T: Data> Label<T> {
         self.size = size.into();
     }
 
+    /// Set the text size.
+    ///
+    /// The argument can be either a `&'static str` or a [`Key<&'static str>`].
+    ///
+    /// [`Key<f64>`]: struct.Key.html
+    pub fn set_font(&mut self, font: impl Into<KeyOrValue<&'static str>>) {
+        self.font = font.into();
+    }
+
     fn get_layout(&mut self, t: &mut PietText, env: &Env) -> PietTextLayout {
-        let font_name = env.get(theme::FONT_NAME);
+        let font_name = self.font.resolve(env);
         let font_size = self.size.resolve(env);
 
         // TODO: caching of both the format and the layout