gpui: Add a standard text example (#30747)

This is a dumb first pass at a standard text example. We'll use this to
start digging in to some text/scale rendering issues.

There will be a ton of follow-up features to this, but starting simple.

Release Notes:

- N/A

crates/gpui/src/colors.rs

@@ -0,0 +1,122 @@
+use crate::{App, Global, Rgba, Window, WindowAppearance, rgb};
+use std::ops::Deref;
+use std::sync::Arc;
+
+/// The default set of colors for gpui.
+///
+/// These are used for styling base components, examples and more.
+#[derive(Clone, Debug)]
+pub struct Colors {
+    /// Text color
+    pub text: Rgba,
+    /// Selected text color
+    pub selected_text: Rgba,
+    /// Background color
+    pub background: Rgba,
+    /// Disabled color
+    pub disabled: Rgba,
+    /// Selected color
+    pub selected: Rgba,
+    /// Border color
+    pub border: Rgba,
+    /// Separator color
+    pub separator: Rgba,
+    /// Container color
+    pub container: Rgba,
+}
+
+impl Default for Colors {
+    fn default() -> Self {
+        Self::light()
+    }
+}
+
+impl Colors {
+    /// Returns the default colors for the given window appearance.
+    pub fn for_appearance(window: &Window) -> Self {
+        match window.appearance() {
+            WindowAppearance::Light | WindowAppearance::VibrantLight => Self::light(),
+            WindowAppearance::Dark | WindowAppearance::VibrantDark => Self::dark(),
+        }
+    }
+
+    /// Returns the default dark colors.
+    pub fn dark() -> Self {
+        Self {
+            text: rgb(0xffffff),
+            selected_text: rgb(0xffffff),
+            disabled: rgb(0x565656),
+            selected: rgb(0x2457ca),
+            background: rgb(0x222222),
+            border: rgb(0x000000),
+            separator: rgb(0xd9d9d9),
+            container: rgb(0x262626),
+        }
+    }
+
+    /// Returns the default light colors.
+    pub fn light() -> Self {
+        Self {
+            text: rgb(0x252525),
+            selected_text: rgb(0xffffff),
+            background: rgb(0xffffff),
+            disabled: rgb(0xb0b0b0),
+            selected: rgb(0x2a63d9),
+            border: rgb(0xd9d9d9),
+            separator: rgb(0xe6e6e6),
+            container: rgb(0xf4f5f5),
+        }
+    }
+
+    /// Get [Colors] from the global state
+    pub fn get_global(cx: &App) -> &Arc<Colors> {
+        &cx.global::<GlobalColors>().0
+    }
+}
+
+/// Get [Colors] from the global state
+#[derive(Clone, Debug)]
+pub struct GlobalColors(pub Arc<Colors>);
+
+impl Deref for GlobalColors {
+    type Target = Arc<Colors>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl Global for GlobalColors {}
+
+/// Implement this trait to allow global [Color] access via `cx.default_colors()`.
+pub trait DefaultColors {
+    /// Returns the default [`gpui::Colors`]
+    fn default_colors(&self) -> &Arc<Colors>;
+}
+
+impl DefaultColors for App {
+    fn default_colors(&self) -> &Arc<Colors> {
+        &self.global::<GlobalColors>().0
+    }
+}
+
+/// The appearance of the base GPUI colors, used to style GPUI elements
+///
+/// Varies based on the system's current [`WindowAppearance`].
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
+pub enum DefaultAppearance {
+    /// Use the set of colors for light appearances.
+    #[default]
+    Light,
+    /// Use the set of colors for dark appearances.
+    Dark,
+}
+
+impl From<WindowAppearance> for DefaultAppearance {
+    fn from(appearance: WindowAppearance) -> Self {
+        match appearance {
+            WindowAppearance::Light | WindowAppearance::VibrantLight => Self::Light,
+            WindowAppearance::Dark | WindowAppearance::VibrantDark => Self::Dark,
+        }
+    }
+}