core: manual buffer sync with sync-rows, reuse unchanged buffers and pipelines across activations

Also lets the screenshot suite point at another reference directory and settle longer.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b2dd-db32-712d-99ce-12ce4a86d979
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

core/render_graph/gpu_resource.rs

@@ -9,6 +9,7 @@ use serde_json::Value;
 use crate::gpu::Wgpu;
 use crate::graph::{Binding, Execution, Extent, Pass, RenderGraph, RenderPipeline, Texture};
 use crate::render_data::RenderData;
+use crate::store::Loadout;
 
 pub struct GpuResources {
     pub buffers: HashMap<String, GpuBuffer>,
@@ -38,6 +39,7 @@ pub struct ProfileMap {
 pub struct GpuBuffer {
     pub buffer: wgpu::Buffer,
     pub source: String,
+    pub usage: wgpu::BufferUsages,
     pub sync_each_frame: bool,
 }
 
@@ -65,28 +67,48 @@ pub enum GpuPass {
 }
 
 impl GpuResources {
+    /// Builds the GPU side of `graph`. Buffers whose source array, size, and usage are unchanged
+    /// and pipelines whose declaration is unchanged are taken over from `previous` instead of being
+    /// recreated and re-uploaded; bind groups and bundles are always rebuilt.
     pub fn activate(
         graph: &RenderGraph,
         gpu: &Wgpu,
         data: &RenderData,
-        previous: Option<&Self>,
+        previous: Option<&Loadout>,
     ) -> Result<Self, String> {
         let mut buffers = HashMap::new();
         for source in &graph.resources.buffers {
             let rows = data.rows(&source.array).ok_or("GRAPH_ARRAY_UNKNOWN")?;
-            let buffer = gpu.device.create_buffer(&wgpu::BufferDescriptor {
-                label: Some(&source.id),
-                size: u64::from(rows.bytes.max(4)),
-                usage: buffer_usage(&source.usage)?,
-                mapped_at_creation: false,
-            });
-            gpu.queue
-                .write_buffer(&buffer, 0, data.bytes(&source.array).unwrap());
+            let size = u64::from(rows.bytes.max(4));
+            let usage = buffer_usage(&source.usage)?;
+            let reused = previous
+                .and_then(|previous| previous.resources.buffers.get(&source.id))
+                .filter(|buffer| {
+                    buffer.source == source.array
+                        && buffer.usage == usage
+                        && buffer.buffer.size() == size
+                })
+                .map(|buffer| buffer.buffer.clone());
+            let buffer = match reused {
+                Some(buffer) => buffer,
+                None => {
+                    let buffer = gpu.device.create_buffer(&wgpu::BufferDescriptor {
+                        label: Some(&source.id),
+                        size,
+                        usage,
+                        mapped_at_creation: false,
+                    });
+                    gpu.queue
+                        .write_buffer(&buffer, 0, data.bytes(&source.array).unwrap());
+                    buffer
+                }
+            };
             buffers.insert(
                 source.id.clone(),
                 GpuBuffer {
                     buffer,
                     source: source.array.clone(),
+                    usage,
                     sync_each_frame: source.sync == "frame",
                 },
             );
@@ -102,11 +124,12 @@ impl GpuResources {
                     let key = source.key()?;
                     if !source.transient {
                         if let Some(texture) = previous
-                            .and_then(|resources| {
-                                resources
+                            .and_then(|previous| {
+                                previous
+                                    .resources
                                     .texture_slots
                                     .get(&source.id)
-                                    .map(|slot| &resources.textures[*slot])
+                                    .map(|slot| &previous.resources.textures[*slot])
                             })
                             .filter(|texture| texture.key == key)
                         {
@@ -147,7 +170,23 @@ impl GpuResources {
             .render
             .iter()
             .map(|source| {
-                create_render_pipeline(source, gpu).map(|pipeline| (source.id.clone(), pipeline))
+                let reused = previous.and_then(|previous| {
+                    previous
+                        .graph
+                        .pipelines
+                        .render
+                        .iter()
+                        .find(|candidate| candidate.same_as(source))
+                        .and_then(|candidate| {
+                            previous.resources.render_pipelines.get(&candidate.id)
+                        })
+                        .cloned()
+                });
+                match reused {
+                    Some(pipeline) => Ok(pipeline),
+                    None => create_render_pipeline(source, gpu),
+                }
+                .map(|pipeline| (source.id.clone(), pipeline))
             })
             .collect::<Result<HashMap<_, _>, _>>()?;
         let compute_pipelines = graph
@@ -155,6 +194,21 @@ impl GpuResources {
             .compute
             .iter()
             .map(|source| {
+                let reused = previous.and_then(|previous| {
+                    previous
+                        .graph
+                        .pipelines
+                        .compute
+                        .iter()
+                        .find(|candidate| candidate.same_as(source))
+                        .and_then(|candidate| {
+                            previous.resources.compute_pipelines.get(&candidate.id)
+                        })
+                        .cloned()
+                });
+                if let Some(pipeline) = reused {
+                    return Ok::<_, String>((source.id.clone(), pipeline));
+                }
                 let module = gpu
                     .device
                     .create_shader_module(wgpu::ShaderModuleDescriptor {
@@ -171,7 +225,7 @@ impl GpuResources {
                             compilation_options: Default::default(),
                             cache: None,
                         });
-                Ok::<_, String>((source.id.clone(), pipeline))
+                Ok((source.id.clone(), pipeline))
             })
             .collect::<Result<HashMap<_, _>, _>>()?;
 
@@ -251,6 +305,28 @@ impl GpuResources {
         Ok(resources)
     }
 
+    /// Copies rows `first .. first + count` of a source array into every GPU buffer bound to it.
+    pub fn sync_rows(
+        &self,
+        name: &str,
+        first: u32,
+        count: u32,
+        gpu: &Wgpu,
+        data: &RenderData,
+    ) -> Result<(), String> {
+        let rows = data.rows(name).ok_or("ROWS_UNKNOWN")?;
+        let end = first
+            .checked_add(count)
+            .filter(|end| *end <= rows.rows)
+            .ok_or("ROW_RANGE")?;
+        let start = (first * rows.stride) as usize;
+        let bytes = &data.bytes(name).unwrap()[start..(end * rows.stride) as usize];
+        for buffer in self.buffers.values().filter(|buffer| buffer.source == name) {
+            gpu.queue.write_buffer(&buffer.buffer, start as u64, bytes);
+        }
+        Ok(())
+    }
+
     pub fn texture_view(&self, id: &str) -> Option<&wgpu::TextureView> {
         self.texture_slots
             .get(id)