1 files changed, 62 insertions, 0 deletions
diff --git a/widget/src/shader/program.rs b/widget/src/shader/program.rs
new file mode 100644
index 00000000..6dd50404
--- /dev/null
+++ b/widget/src/shader/program.rs
@@ -0,0 +1,62 @@
+use crate::core::event;
+use crate::core::mouse;
+use crate::core::{Rectangle, Shell};
+use crate::renderer::wgpu::primitive::pipeline;
+use crate::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::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: pipeline::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::Shader
+    fn mouse_interaction(
+        &self,
+        _state: &Self::State,
+        _bounds: Rectangle,
+        _cursor: mouse::Cursor,
+    ) -> mouse::Interaction {
+        mouse::Interaction::default()
+    }
+}