Redesign `iced_wgpu` layering architecture

1 files changed, 214 insertions, 80 deletions

diff --git a/wgpu/src/quad.rs b/wgpu/src/quad.rs
index 0717a031..16d50b04 100644
--- a/wgpu/src/quad.rs
+++ b/wgpu/src/quad.rs
@@ -12,11 +12,37 @@ use bytemuck::{Pod, Zeroable};
 
 use std::mem;
 
-#[cfg(feature = "tracing")]
-use tracing::info_span;
-
 const INITIAL_INSTANCES: usize = 2_000;
 
+/// The properties of a quad.
+#[derive(Clone, Copy, Debug, Pod, Zeroable)]
+#[repr(C)]
+pub struct Quad {
+    /// The position of the [`Quad`].
+    pub position: [f32; 2],
+
+    /// The size of the [`Quad`].
+    pub size: [f32; 2],
+
+    /// The border color of the [`Quad`], in __linear RGB__.
+    pub border_color: color::Packed,
+
+    /// The border radii of the [`Quad`].
+    pub border_radius: [f32; 4],
+
+    /// The border width of the [`Quad`].
+    pub border_width: f32,
+
+    /// The shadow color of the [`Quad`].
+    pub shadow_color: color::Packed,
+
+    /// The shadow offset of the [`Quad`].
+    pub shadow_offset: [f32; 2],
+
+    /// The shadow blur radius of the [`Quad`].
+    pub shadow_blur_radius: f32,
+}
+
 #[derive(Debug)]
 pub struct Pipeline {
     solid: solid::Pipeline,
@@ -54,7 +80,7 @@ impl Pipeline {
         }
     }
 
-    pub fn prepare(
+    pub fn prepare_batch(
         &mut self,
         device: &wgpu::Device,
         encoder: &mut wgpu::CommandEncoder,
@@ -73,7 +99,64 @@ impl Pipeline {
         self.prepare_layer += 1;
     }
 
-    pub fn render<'a>(
+    pub fn prepare_cache(
+        &self,
+        device: &wgpu::Device,
+        encoder: &mut wgpu::CommandEncoder,
+        belt: &mut wgpu::util::StagingBelt,
+        cache: &mut Cache,
+        transformation: Transformation,
+        scale: f32,
+    ) {
+        match cache {
+            Cache::Staged(_) => {
+                let Cache::Staged(batch) =
+                    std::mem::replace(cache, Cache::Staged(Batch::default()))
+                else {
+                    unreachable!()
+                };
+
+                let mut layer = Layer::new(device, &self.constant_layout);
+                layer.prepare(
+                    device,
+                    encoder,
+                    belt,
+                    &batch,
+                    transformation,
+                    scale,
+                );
+
+                *cache = Cache::Uploaded {
+                    layer,
+                    batch,
+                    needs_reupload: false,
+                }
+            }
+
+            Cache::Uploaded {
+                batch,
+                layer,
+                needs_reupload,
+            } => {
+                if *needs_reupload {
+                    layer.prepare(
+                        device,
+                        encoder,
+                        belt,
+                        batch,
+                        transformation,
+                        scale,
+                    );
+
+                    *needs_reupload = false;
+                } else {
+                    layer.update(device, encoder, belt, transformation, scale);
+                }
+            }
+        }
+    }
+
+    pub fn render_batch<'a>(
         &'a self,
         layer: usize,
         bounds: Rectangle<u32>,
@@ -81,38 +164,59 @@ impl Pipeline {
         render_pass: &mut wgpu::RenderPass<'a>,
     ) {
         if let Some(layer) = self.layers.get(layer) {
-            render_pass.set_scissor_rect(
-                bounds.x,
-                bounds.y,
-                bounds.width,
-                bounds.height,
-            );
-
-            let mut solid_offset = 0;
-            let mut gradient_offset = 0;
-
-            for (kind, count) in &quads.order {
-                match kind {
-                    Kind::Solid => {
-                        self.solid.render(
-                            render_pass,
-                            &layer.constants,
-                            &layer.solid,
-                            solid_offset..(solid_offset + count),
-                        );
-
-                        solid_offset += count;
-                    }
-                    Kind::Gradient => {
-                        self.gradient.render(
-                            render_pass,
-                            &layer.constants,
-                            &layer.gradient,
-                            gradient_offset..(gradient_offset + count),
-                        );
-
-                        gradient_offset += count;
-                    }
+            self.render(bounds, layer, &quads.order, render_pass);
+        }
+    }
+
+    pub fn render_cache<'a>(
+        &'a self,
+        cache: &'a Cache,
+        bounds: Rectangle<u32>,
+        render_pass: &mut wgpu::RenderPass<'a>,
+    ) {
+        if let Cache::Uploaded { layer, batch, .. } = cache {
+            self.render(bounds, layer, &batch.order, render_pass);
+        }
+    }
+
+    fn render<'a>(
+        &'a self,
+        bounds: Rectangle<u32>,
+        layer: &'a Layer,
+        order: &Order,
+        render_pass: &mut wgpu::RenderPass<'a>,
+    ) {
+        render_pass.set_scissor_rect(
+            bounds.x,
+            bounds.y,
+            bounds.width,
+            bounds.height,
+        );
+
+        let mut solid_offset = 0;
+        let mut gradient_offset = 0;
+
+        for (kind, count) in order {
+            match kind {
+                Kind::Solid => {
+                    self.solid.render(
+                        render_pass,
+                        &layer.constants,
+                        &layer.solid,
+                        solid_offset..(solid_offset + count),
+                    );
+
+                    solid_offset += count;
+                }
+                Kind::Gradient => {
+                    self.gradient.render(
+                        render_pass,
+                        &layer.constants,
+                        &layer.gradient,
+                        gradient_offset..(gradient_offset + count),
+                    );
+
+                    gradient_offset += count;
                 }
             }
         }
@@ -124,7 +228,49 @@ impl Pipeline {
 }
 
 #[derive(Debug)]
-struct Layer {
+pub enum Cache {
+    Staged(Batch),
+    Uploaded {
+        batch: Batch,
+        layer: Layer,
+        needs_reupload: bool,
+    },
+}
+
+impl Cache {
+    pub fn is_empty(&self) -> bool {
+        match self {
+            Cache::Staged(batch) | Cache::Uploaded { batch, .. } => {
+                batch.is_empty()
+            }
+        }
+    }
+
+    pub fn update(&mut self, new_batch: Batch) {
+        match self {
+            Self::Staged(batch) => {
+                *batch = new_batch;
+            }
+            Self::Uploaded {
+                batch,
+                needs_reupload,
+                ..
+            } => {
+                *batch = new_batch;
+                *needs_reupload = true;
+            }
+        }
+    }
+}
+
+impl Default for Cache {
+    fn default() -> Self {
+        Self::Staged(Batch::default())
+    }
+}
+
+#[derive(Debug)]
+pub struct Layer {
     constants: wgpu::BindGroup,
     constants_buffer: wgpu::Buffer,
     solid: solid::Layer,
@@ -169,9 +315,26 @@ impl Layer {
         transformation: Transformation,
         scale: f32,
     ) {
-        #[cfg(feature = "tracing")]
-        let _ = info_span!("Wgpu::Quad", "PREPARE").entered();
+        self.update(device, encoder, belt, transformation, scale);
+
+        if !quads.solids.is_empty() {
+            self.solid.prepare(device, encoder, belt, &quads.solids);
+        }
+
+        if !quads.gradients.is_empty() {
+            self.gradient
+                .prepare(device, encoder, belt, &quads.gradients);
+        }
+    }
 
+    pub fn update(
+        &mut self,
+        device: &wgpu::Device,
+        encoder: &mut wgpu::CommandEncoder,
+        belt: &mut wgpu::util::StagingBelt,
+        transformation: Transformation,
+        scale: f32,
+    ) {
         let uniforms = Uniforms::new(transformation, scale);
         let bytes = bytemuck::bytes_of(&uniforms);
 
@@ -183,47 +346,9 @@ impl Layer {
             device,
         )
         .copy_from_slice(bytes);
-
-        if !quads.solids.is_empty() {
-            self.solid.prepare(device, encoder, belt, &quads.solids);
-        }
-
-        if !quads.gradients.is_empty() {
-            self.gradient
-                .prepare(device, encoder, belt, &quads.gradients);
-        }
     }
 }
 
-/// The properties of a quad.
-#[derive(Clone, Copy, Debug, Pod, Zeroable)]
-#[repr(C)]
-pub struct Quad {
-    /// The position of the [`Quad`].
-    pub position: [f32; 2],
-
-    /// The size of the [`Quad`].
-    pub size: [f32; 2],
-
-    /// The border color of the [`Quad`], in __linear RGB__.
-    pub border_color: color::Packed,
-
-    /// The border radii of the [`Quad`].
-    pub border_radius: [f32; 4],
-
-    /// The border width of the [`Quad`].
-    pub border_width: f32,
-
-    /// The shadow color of the [`Quad`].
-    pub shadow_color: [f32; 4],
-
-    /// The shadow offset of the [`Quad`].
-    pub shadow_offset: [f32; 2],
-
-    /// The shadow blur radius of the [`Quad`].
-    pub shadow_blur_radius: f32,
-}
-
 /// A group of [`Quad`]s rendered together.
 #[derive(Default, Debug)]
 pub struct Batch {
@@ -233,10 +358,13 @@ pub struct Batch {
     /// The gradient quads of the [`Layer`].
     gradients: Vec<Gradient>,
 
-    /// The quad order of the [`Layer`]; stored as a tuple of the quad type & its count.
-    order: Vec<(Kind, usize)>,
+    /// The quad order of the [`Layer`].
+    order: Order,
 }
 
+/// The quad order of a [`Layer`]; stored as a tuple of the quad type & its count.
+type Order = Vec<(Kind, usize)>;
+
 impl Batch {
     /// Returns true if there are no quads of any type in [`Quads`].
     pub fn is_empty(&self) -> bool {
@@ -276,6 +404,12 @@ impl Batch {
             }
         }
     }
+
+    pub fn clear(&mut self) {
+        self.solids.clear();
+        self.gradients.clear();
+        self.order.clear();
+    }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]