Re-organize custom module as pipeline module

... and move `Shader` widget to `iced_widget` crate

wgpu/src/primitive/pipeline.rs

@@ -0,0 +1,117 @@
+//! Draw primitives using custom pipelines.
+use crate::core::{Rectangle, Size};
+use crate::graphics::Transformation;
+
+use std::any::{Any, TypeId};
+use std::collections::HashMap;
+use std::fmt::Debug;
+use std::sync::Arc;
+
+#[derive(Clone, Debug)]
+/// A custom primitive which can be used to render primitives associated with a custom pipeline.
+pub struct Pipeline {
+    /// The bounds of the [`Shader`].
+    pub bounds: Rectangle,
+
+    /// The [`custom::Primitive`] to render.
+    pub primitive: Arc<dyn Primitive>,
+}
+
+impl Pipeline {
+    /// Creates a new [`Pipeline`] with the given [`Primitive`].
+    pub fn new(bounds: Rectangle, primitive: impl Primitive) -> Self {
+        Pipeline {
+            bounds,
+            primitive: Arc::new(primitive),
+        }
+    }
+}
+
+impl PartialEq for Pipeline {
+    fn eq(&self, other: &Self) -> bool {
+        self.primitive.type_id() == other.primitive.type_id()
+    }
+}
+
+/// A set of methods which allows a [`Primitive`] to be rendered.
+pub trait Primitive: Debug + Send + Sync + 'static {
+    /// Processes the [`Primitive`], allowing for GPU buffer allocation.
+    fn prepare(
+        &self,
+        format: wgpu::TextureFormat,
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        target_size: Size<u32>,
+        scale_factor: f32,
+        transform: Transformation,
+        storage: &mut Storage,
+    );
+
+    /// Renders the [`Primitive`].
+    fn render(
+        &self,
+        storage: &Storage,
+        bounds: Rectangle<u32>,
+        target: &wgpu::TextureView,
+        target_size: Size<u32>,
+        encoder: &mut wgpu::CommandEncoder,
+    );
+}
+
+/// A renderer than can draw custom pipeline primitives.
+pub trait Renderer: crate::core::Renderer {
+    /// Draws a custom pipeline primitive.
+    fn draw_pipeline_primitive(
+        &mut self,
+        bounds: Rectangle,
+        primitive: impl Primitive,
+    );
+}
+
+impl<Theme> Renderer for crate::Renderer<Theme> {
+    fn draw_pipeline_primitive(
+        &mut self,
+        bounds: Rectangle,
+        primitive: impl Primitive,
+    ) {
+        self.draw_primitive(super::Primitive::Custom(super::Custom::Pipeline(
+            Pipeline::new(bounds, primitive),
+        )));
+    }
+}
+
+/// Stores custom, user-provided pipelines.
+#[derive(Default, Debug)]
+pub struct Storage {
+    pipelines: HashMap<TypeId, Box<dyn Any>>,
+}
+
+impl Storage {
+    /// Returns `true` if `Storage` contains a pipeline with type `T`.
+    pub fn has<T: 'static>(&self) -> bool {
+        self.pipelines.get(&TypeId::of::<T>()).is_some()
+    }
+
+    /// Inserts the pipeline `T` in to [`Storage`].
+    pub fn store<T: 'static>(&mut self, pipeline: T) {
+        let _ = self.pipelines.insert(TypeId::of::<T>(), Box::new(pipeline));
+    }
+
+    /// Returns a reference to pipeline with type `T` if it exists in [`Storage`].
+    pub fn get<T: 'static>(&self) -> Option<&T> {
+        self.pipelines.get(&TypeId::of::<T>()).map(|pipeline| {
+            pipeline
+                .downcast_ref::<T>()
+                .expect("Pipeline with this type does not exist in Storage.")
+        })
+    }
+
+    /// Returns a mutable reference to pipeline `T` if it exists in [`Storage`].
+    pub fn get_mut<T: 'static>(&mut self) -> Option<&mut T> {
+        self.pipelines.get_mut(&TypeId::of::<T>()).map(|pipeline| {
+            pipeline
+                .downcast_mut::<T>()
+                .expect("Pipeline with this type does not exist in Storage.")
+        })
+    }
+}