3 files changed, 296 insertions, 0 deletions
diff --git a/renderer/src/widget/shader.rs b/renderer/src/widget/shader.rs
new file mode 100644
index 00000000..da42a7dd
--- /dev/null
+++ b/renderer/src/widget/shader.rs
@@ -0,0 +1,215 @@
+//! A custom shader widget for wgpu applications.
+use crate::core::event::Status;
+use crate::core::layout::{Limits, Node};
+use crate::core::mouse::{Cursor, Interaction};
+use crate::core::renderer::Style;
+use crate::core::widget::tree::{State, Tag};
+use crate::core::widget::{tree, Tree};
+use crate::core::{
+    self, layout, mouse, widget, Clipboard, Element, Layout, Length, Rectangle,
+    Shell, Size, Widget,
+};
+use std::marker::PhantomData;
+
+mod event;
+mod program;
+
+pub use event::Event;
+pub use iced_wgpu::custom::Primitive;
+pub use iced_wgpu::custom::Storage;
+pub use program::Program;
+
+/// A widget which can render custom shaders with Iced's `wgpu` backend.
+///
+/// Must be initialized with a [`Program`], which describes the internal widget state & how
+/// its [`Program::Primitive`]s are drawn.
+#[allow(missing_debug_implementations)]
+pub struct Shader<Message, P: Program<Message>> {
+    width: Length,
+    height: Length,
+    program: P,
+    _message: PhantomData<Message>,
+}
+
+impl<Message, P: Program<Message>> Shader<Message, P> {
+    /// Create a new custom [`Shader`].
+    pub fn new(program: P) -> Self {
+        Self {
+            width: Length::Fixed(100.0),
+            height: Length::Fixed(100.0),
+            program,
+            _message: PhantomData,
+        }
+    }
+
+    /// Set the `width` of the custom [`Shader`].
+    pub fn width(mut self, width: impl Into<Length>) -> Self {
+        self.width = width.into();
+        self
+    }
+
+    /// Set the `height` of the custom [`Shader`].
+    pub fn height(mut self, height: impl Into<Length>) -> Self {
+        self.height = height.into();
+        self
+    }
+}
+
+impl<P, Message, Theme> Widget<Message, crate::Renderer<Theme>>
+    for Shader<Message, P>
+where
+    P: Program<Message>,
+{
+    fn tag(&self) -> Tag {
+        struct Tag<T>(T);
+        tree::Tag::of::<Tag<P::State>>()
+    }
+
+    fn state(&self) -> State {
+        tree::State::new(P::State::default())
+    }
+
+    fn width(&self) -> Length {
+        self.width
+    }
+
+    fn height(&self) -> Length {
+        self.height
+    }
+
+    fn layout(
+        &self,
+        _tree: &mut Tree,
+        _renderer: &crate::Renderer<Theme>,
+        limits: &Limits,
+    ) -> Node {
+        let limits = limits.width(self.width).height(self.height);
+        let size = limits.resolve(Size::ZERO);
+
+        layout::Node::new(size)
+    }
+
+    fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: crate::core::Event,
+        layout: Layout<'_>,
+        cursor: Cursor,
+        _renderer: &crate::Renderer<Theme>,
+        _clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        _viewport: &Rectangle,
+    ) -> Status {
+        let bounds = layout.bounds();
+
+        let custom_shader_event = match event {
+            core::Event::Mouse(mouse_event) => Some(Event::Mouse(mouse_event)),
+            core::Event::Keyboard(keyboard_event) => {
+                Some(Event::Keyboard(keyboard_event))
+            }
+            core::Event::Touch(touch_event) => Some(Event::Touch(touch_event)),
+            _ => None,
+        };
+
+        if let Some(custom_shader_event) = custom_shader_event {
+            let state = tree.state.downcast_mut::<P::State>();
+
+            let (event_status, message) = self.program.update(
+                state,
+                custom_shader_event,
+                bounds,
+                cursor,
+                shell,
+            );
+
+            if let Some(message) = message {
+                shell.publish(message);
+            }
+
+            return event_status;
+        }
+
+        event::Status::Ignored
+    }
+
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor: Cursor,
+        _viewport: &Rectangle,
+        _renderer: &crate::Renderer<Theme>,
+    ) -> mouse::Interaction {
+        let bounds = layout.bounds();
+        let state = tree.state.downcast_ref::<P::State>();
+
+        self.program.mouse_interaction(state, bounds, cursor)
+    }
+
+    fn draw(
+        &self,
+        tree: &widget::Tree,
+        renderer: &mut crate::Renderer<Theme>,
+        _theme: &Theme,
+        _style: &Style,
+        layout: Layout<'_>,
+        cursor_position: mouse::Cursor,
+        _viewport: &Rectangle,
+    ) {
+        let bounds = layout.bounds();
+        let state = tree.state.downcast_ref::<P::State>();
+
+        renderer.draw_custom(
+            bounds,
+            self.program.draw(state, cursor_position, bounds),
+        );
+    }
+}
+
+impl<'a, M, P, Theme> From<Shader<M, P>>
+    for Element<'a, M, crate::Renderer<Theme>>
+where
+    M: 'a,
+    P: Program<M> + 'a,
+{
+    fn from(custom: Shader<M, P>) -> Element<'a, M, crate::Renderer<Theme>> {
+        Element::new(custom)
+    }
+}
+
+impl<Message, T> Program<Message> for &T
+where
+    T: Program<Message>,
+{
+    type State = T::State;
+    type Primitive = T::Primitive;
+
+    fn update(
+        &self,
+        state: &mut Self::State,
+        event: Event,
+        bounds: Rectangle,
+        cursor: Cursor,
+        shell: &mut Shell<'_, Message>,
+    ) -> (Status, Option<Message>) {
+        T::update(self, state, event, bounds, cursor, shell)
+    }
+
+    fn draw(
+        &self,
+        state: &Self::State,
+        cursor: Cursor,
+        bounds: Rectangle,
+    ) -> Self::Primitive {
+        T::draw(self, state, cursor, bounds)
+    }
+
+    fn mouse_interaction(
+        &self,
+        state: &Self::State,
+        bounds: Rectangle,
+        cursor: Cursor,
+    ) -> Interaction {
+        T::mouse_interaction(self, state, bounds, cursor)
+    }
+}
diff --git a/renderer/src/widget/shader/event.rs b/renderer/src/widget/shader/event.rs
new file mode 100644
index 00000000..981b30d7
--- /dev/null
+++ b/renderer/src/widget/shader/event.rs
@@ -0,0 +1,21 @@
+//! Handle events of a custom shader widget.
+use crate::core::keyboard;
+use crate::core::mouse;
+use crate::core::touch;
+
+pub use crate::core::event::Status;
+
+/// A [`Shader`] event.
+///
+/// [`Shader`]: crate::widget::shader::Shader;
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Event {
+    /// A mouse event.
+    Mouse(mouse::Event),
+
+    /// A touch event.
+    Touch(touch::Event),
+
+    /// A keyboard event.
+    Keyboard(keyboard::Event),
+}
diff --git a/renderer/src/widget/shader/program.rs b/renderer/src/widget/shader/program.rs
new file mode 100644
index 00000000..b8871688
--- /dev/null
+++ b/renderer/src/widget/shader/program.rs
@@ -0,0 +1,60 @@
+use crate::core::{event, mouse, Rectangle, Shell};
+use crate::widget;
+use widget::shader;
+
+/// The state and logic of a [`Shader`] widget.
+///
+/// A [`Program`] can mutate the internal state of a [`Shader`] widget
+/// and produce messages for an application.
+///
+/// [`Shader`]: crate::widget::shader::Shader
+pub trait Program<Message> {
+    /// The internal state of the [`Program`].
+    type State: Default + 'static;
+
+    /// The type of primitive this [`Program`] can draw.
+    type Primitive: shader::Primitive + 'static;
+
+    /// Update the internal [`State`] of the [`Program`]. This can be used to reflect state changes
+    /// based on mouse & other events. You can use the [`Shell`] to publish messages, request a
+    /// redraw for the window, etc.
+    ///
+    /// By default, this method does and returns nothing.
+    ///
+    /// [`State`]: Self::State
+    fn update(
+        &self,
+        _state: &mut Self::State,
+        _event: shader::Event,
+        _bounds: Rectangle,
+        _cursor: mouse::Cursor,
+        _shell: &mut Shell<'_, Message>,
+    ) -> (event::Status, Option<Message>) {
+        (event::Status::Ignored, None)
+    }
+
+    /// Draws the [`Primitive`].
+    ///
+    /// [`Primitive`]: Self::Primitive
+    fn draw(
+        &self,
+        state: &Self::State,
+        cursor: mouse::Cursor,
+        bounds: Rectangle,
+    ) -> Self::Primitive;
+
+    /// Returns the current mouse interaction of the [`Program`].
+    ///
+    /// The interaction returned will be in effect even if the cursor position is out of
+    /// bounds of the [`Shader`]'s program.
+    ///
+    /// [`Shader`]: crate::widget::shader::Shader
+    fn mouse_interaction(
+        &self,
+        _state: &Self::State,
+        _bounds: Rectangle,
+        _cursor: mouse::Cursor,
+    ) -> mouse::Interaction {
+        mouse::Interaction::default()
+    }
+}