3 files changed, 180 insertions, 0 deletions

diff --git a/native/src/renderer.rs b/native/src/renderer.rs
index 833de571..7a68ada4 100644
--- a/native/src/renderer.rs
+++ b/native/src/renderer.rs
@@ -21,16 +21,32 @@
 //! [`checkbox::Renderer`]: ../widget/checkbox/trait.Renderer.html
 
 mod debugger;
+#[cfg(debug_assertions)]
+mod null;
 mod windowed;
 
 pub use debugger::Debugger;
+#[cfg(debug_assertions)]
+pub use null::Null;
 pub use windowed::{Target, Windowed};
 
 use crate::{layout, Element};
 
+/// A component that can take the state of a user interface and produce an
+/// output for its users.
 pub trait Renderer: Sized {
+    /// The type of output of the [`Renderer`].
+    ///
+    /// If you are implementing a graphical renderer, your output will most
+    /// likely be a tree of visual primitives.
+    ///
+    /// [`Renderer`]: trait.Renderer.html
     type Output;
 
+    /// Lays out the elements of a user interface.
+    ///
+    /// You should override this if you need to perform any operations before or
+    /// after layouting. For instance, trimming the measurements cache.
     fn layout<'a, Message>(
         &mut self,
         element: &Element<'a, Message, Self>,
diff --git a/native/src/renderer/null.rs b/native/src/renderer/null.rs
new file mode 100644
index 00000000..182f033a
--- /dev/null
+++ b/native/src/renderer/null.rs
@@ -0,0 +1,145 @@
+use crate::{
+    button, checkbox, column, radio, row, scrollable, text, text_input,
+    Background, Color, Element, Font, HorizontalAlignment, Layout, Point,
+    Rectangle, Renderer, Size, VerticalAlignment,
+};
+
+/// A renderer that does nothing.
+#[derive(Debug, Clone, Copy)]
+pub struct Null;
+
+impl Renderer for Null {
+    type Output = ();
+}
+
+impl column::Renderer for Null {
+    fn draw<Message>(
+        &mut self,
+        _content: &[Element<'_, Message, Self>],
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+    ) {
+    }
+}
+
+impl row::Renderer for Null {
+    fn draw<Message>(
+        &mut self,
+        _content: &[Element<'_, Message, Self>],
+        _layout: Layout<'_>,
+        _cursor_position: Point,
+    ) {
+    }
+}
+
+impl text::Renderer for Null {
+    fn default_size(&self) -> u16 {
+        20
+    }
+
+    fn measure(
+        &self,
+        _content: &str,
+        _size: u16,
+        _font: Font,
+        _bounds: Size,
+    ) -> (f32, f32) {
+        (0.0, 20.0)
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _content: &str,
+        _size: u16,
+        _font: Font,
+        _color: Option<Color>,
+        _horizontal_alignment: HorizontalAlignment,
+        _vertical_alignment: VerticalAlignment,
+    ) {
+    }
+}
+
+impl scrollable::Renderer for Null {
+    fn is_mouse_over_scrollbar(
+        &self,
+        _bounds: Rectangle,
+        _content_bounds: Rectangle,
+        _cursor_position: Point,
+    ) -> bool {
+        false
+    }
+
+    fn draw(
+        &mut self,
+        _scrollable: &scrollable::State,
+        _bounds: Rectangle,
+        _content_bounds: Rectangle,
+        _is_mouse_over: bool,
+        _is_mouse_over_scrollbar: bool,
+        _offset: u32,
+        _content: Self::Output,
+    ) {
+    }
+}
+
+impl text_input::Renderer for Null {
+    fn default_size(&self) -> u16 {
+        20
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _text_bounds: Rectangle,
+        _cursor_position: Point,
+        _size: u16,
+        _placeholder: &str,
+        _value: &text_input::Value,
+        _state: &text_input::State,
+    ) -> Self::Output {
+    }
+}
+
+impl button::Renderer for Null {
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _cursor_position: Point,
+        _is_pressed: bool,
+        _background: Option<Background>,
+        _border_radius: u16,
+        _content: Self::Output,
+    ) -> Self::Output {
+    }
+}
+
+impl radio::Renderer for Null {
+    fn default_size(&self) -> u32 {
+        20
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _is_selected: bool,
+        _is_mouse_over: bool,
+        _label: Self::Output,
+    ) {
+    }
+}
+
+impl checkbox::Renderer for Null {
+    fn default_size(&self) -> u32 {
+        20
+    }
+
+    fn draw(
+        &mut self,
+        _bounds: Rectangle,
+        _is_checked: bool,
+        _is_mouse_over: bool,
+        _label: Self::Output,
+    ) {
+    }
+}
diff --git a/native/src/renderer/windowed.rs b/native/src/renderer/windowed.rs
index 6d0419d2..813a03f2 100644
--- a/native/src/renderer/windowed.rs
+++ b/native/src/renderer/windowed.rs
@@ -2,11 +2,21 @@ use crate::MouseCursor;
 
 use raw_window_handle::HasRawWindowHandle;
 
+/// A renderer that can target windows.
 pub trait Windowed: super::Renderer + Sized {
+    /// The type of target.
     type Target: Target<Renderer = Self>;
 
+    /// Creates a new [`Windowed`] renderer.
+    ///
+    /// [`Windowed`]: trait.Windowed.html
     fn new() -> Self;
 
+    /// Performs the drawing operations described in the output on the given
+    /// target.
+    ///
+    /// The overlay can be a bunch of debug text logs. It should be rendered on
+    /// top of the GUI on most scenarios.
     fn draw<T: AsRef<str>>(
         &mut self,
         output: &Self::Output,
@@ -15,9 +25,15 @@ pub trait Windowed: super::Renderer + Sized {
     ) -> MouseCursor;
 }
 
+/// A rendering target.
 pub trait Target {
+    /// The renderer of this target.
     type Renderer;
 
+    /// Creates a new rendering [`Target`] from the given window handle, width,
+    /// height and dpi factor.
+    ///
+    /// [`Target`]: trait.Target.html
     fn new<W: HasRawWindowHandle>(
         window: &W,
         width: u16,
@@ -26,6 +42,9 @@ pub trait Target {
         renderer: &Self::Renderer,
     ) -> Self;
 
+    /// Resizes the current [`Target`].
+    ///
+    /// [`Target`]: trait.Target.html
     fn resize(
         &mut self,
         width: u16,