6 files changed, 229 insertions, 0 deletions
diff --git a/src/components.rs b/src/components.rs
new file mode 100644
index 0000000..3179f0c
--- /dev/null
+++ b/src/components.rs
@@ -0,0 +1,33 @@
+use std::sync::{Mutex, Arc};
+
+use bevy::{prelude::*, render::extract_component::ExtractComponent, ecs::query::QueryItem};
+
+use crate::render_assets::FramebufferExtractSource;
+
+#[derive(Component, Default, Clone)]
+pub struct FramebufferExtractDestination(pub Arc<Mutex<Image>>);
+
+impl ExtractComponent for FramebufferExtractDestination {
+    type QueryData = (
+        &'static Self,
+        &'static Handle<FramebufferExtractSource>,
+    );
+
+    type QueryFilter = ();
+
+    type Out = (Self, Handle<FramebufferExtractSource>);
+
+    fn extract_component((destination, source_handle): QueryItem<'_, Self::QueryData>) -> Option<Self::Out> {
+        Some((
+            destination.clone(),
+            source_handle.clone(),
+        ))
+    }
+}
+
+#[derive(Bundle)]
+pub struct ExtractFramebufferBundle {
+    pub source: Handle<FramebufferExtractSource>,
+    pub dest: FramebufferExtractDestination,
+}
+
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..9c6fb1b
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,41 @@
+use bevy::{prelude::*, render::{render_asset::RenderAssetPlugin, extract_component::ExtractComponentPlugin, RenderApp, Render, RenderSet, render_graph::RenderGraph, graph::CameraDriverLabel}};
+use components::FramebufferExtractDestination;
+use nodes::{FramebufferExtractNode, FramebufferExtractLabel};
+use render_assets::FramebufferExtractSource;
+
+pub mod components;
+mod systems;
+mod nodes;
+pub mod render_assets;
+
+
+pub enum FramebufferExtractSet {
+    Set
+}
+
+pub struct FramebufferExtractPlugin;
+
+impl Plugin for FramebufferExtractPlugin {
+    fn build(&self, app: &mut App) {
+        app
+            .register_type::<FramebufferExtractSource>()
+            .init_asset::<FramebufferExtractSource>()
+            .register_asset_reflect::<FramebufferExtractSource>()
+            .add_plugins((
+                RenderAssetPlugin::<FramebufferExtractSource>::default(),
+                ExtractComponentPlugin::<FramebufferExtractDestination>::default(),
+            ));
+
+        let render_app = app.sub_app_mut(RenderApp);
+        render_app
+            .add_systems(
+                Render,
+                systems::extract_framebuffers
+                    .after(RenderSet::Render)
+                    .before(RenderSet::Cleanup),
+            );
+        let mut graph = render_app.world.resource_mut::<RenderGraph>();
+        graph.add_node(FramebufferExtractLabel, FramebufferExtractNode);
+        graph.add_node_edge(CameraDriverLabel, FramebufferExtractLabel);
+    }
+}
diff --git a/src/nodes.rs b/src/nodes.rs
new file mode 100644
index 0000000..bccd861
--- /dev/null
+++ b/src/nodes.rs
@@ -0,0 +1,38 @@
+use bevy::{prelude::*, render::{render_graph::{Node, RenderGraphContext, NodeRunError, RenderLabel}, renderer::RenderContext, render_asset::RenderAssets, render_resource::{ImageCopyBuffer, ImageDataLayout}}};
+
+use crate::render_assets::FramebufferExtractSource;
+
+#[derive(RenderLabel, Clone, PartialEq, Eq, Debug, Hash)]
+pub struct FramebufferExtractLabel;
+
+#[derive(Default)]
+pub struct FramebufferExtractNode;
+
+impl Node for FramebufferExtractNode {
+    fn run(
+        &self,
+        graph: &mut RenderGraphContext,
+        render_context: &mut RenderContext,
+        world: &World,
+    ) -> Result<(), NodeRunError> {
+        for (_, source) in world.resource::<RenderAssets<FramebufferExtractSource>>().iter() {
+            let Some(gpu_image) = world.resource::<RenderAssets<Image>>().get(&source.source_handle) else {
+                return Ok(())
+            };
+
+            render_context.command_encoder().copy_texture_to_buffer(
+                gpu_image.texture.as_image_copy(),
+                ImageCopyBuffer {
+                    buffer: &source.buffer,
+                    layout: ImageDataLayout {
+                        offset: 0,
+                        bytes_per_row: Some(source.padded_bytes_per_row),
+                        rows_per_image: None,
+                    },
+                },
+                source.source_size,
+            );
+        }
+        Ok(())
+    }
+}
diff --git a/src/render_assets.rs b/src/render_assets.rs
new file mode 100644
index 0000000..1615e01
--- /dev/null
+++ b/src/render_assets.rs
@@ -0,0 +1,52 @@
+use bevy::{prelude::*, render::{render_asset::{RenderAsset, RenderAssets, RenderAssetUsages, PrepareAssetError}, render_resource::{Buffer, Extent3d, BufferUsages, BufferDescriptor, TextureFormat}, renderer::RenderDevice}, ecs::system::{lifetimeless::SRes, SystemParamItem}};
+
+pub struct GpuFramebufferExtractSource {
+    pub buffer: Buffer,
+    pub source_handle: Handle<Image>,
+    pub source_size: Extent3d,
+    pub bytes_per_row: u32,
+    pub padded_bytes_per_row: u32,
+    pub format: TextureFormat,
+}
+
+#[derive(Asset, Reflect, Clone, Default)]
+pub struct FramebufferExtractSource(pub Handle<Image>);
+
+impl RenderAsset for FramebufferExtractSource {
+    type PreparedAsset = GpuFramebufferExtractSource;
+    type Param = (SRes<RenderDevice>, SRes<RenderAssets<Image>>);
+
+    fn asset_usage(&self) -> RenderAssetUsages {
+        RenderAssetUsages::default()
+    }
+
+    fn prepare_asset(
+        self,
+        (device, images): &mut SystemParamItem<Self::Param>,
+    ) -> Result<Self::PreparedAsset, PrepareAssetError<Self>> {
+        
+        let Some(gpu_image) = images.get(&self.0) else {
+            warn!("Failed to get GPU image");
+            return Err(PrepareAssetError::RetryNextUpdate(self))
+        };
+
+        let size = gpu_image.texture.size();
+        let format = gpu_image.texture_format;
+        let bytes_per_row = (size.width / format.block_dimensions().0) * format.block_copy_size(None).unwrap();
+        let padded_bytes_per_row = RenderDevice::align_copy_bytes_per_row(bytes_per_row as usize) as u32;
+
+        Ok(GpuFramebufferExtractSource {
+            buffer: device.create_buffer(&BufferDescriptor { 
+                label: Some("framebuffer_extract_buffer"),
+                size: (size.height * padded_bytes_per_row) as u64,
+                usage: BufferUsages::COPY_DST | BufferUsages::MAP_READ,
+                mapped_at_creation: false,
+            }),
+            source_handle: self.0.clone(),
+            source_size: size,
+            bytes_per_row,
+            padded_bytes_per_row,
+            format,
+        })
+    }
+}
diff --git a/src/resources.rs b/src/resources.rs
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/src/resources.rs
diff --git a/src/systems.rs b/src/systems.rs
new file mode 100644
index 0000000..25b25dc
--- /dev/null
+++ b/src/systems.rs
@@ -0,0 +1,65 @@
+use std::time::Duration;
+
+use bevy::{prelude::*, render::{render_asset::{RenderAssets, RenderAssetUsages}, renderer::RenderDevice, render_resource::{MapMode, Maintain, Extent3d, TextureDimension}}};
+
+use pollster::FutureExt;
+
+use crate::{render_assets::FramebufferExtractSource, components::FramebufferExtractDestination};
+
+pub fn extract_framebuffers(
+    mut extract_bundles: Query<(&Handle<FramebufferExtractSource>, &mut FramebufferExtractDestination)>, 
+    sources: Res<RenderAssets<FramebufferExtractSource>>,
+    device: Res<RenderDevice>,
+) {
+    for (source_handle, destination_handle) in extract_bundles.iter_mut() {
+        let Some(gpu_source) = sources.get(source_handle) else {
+            continue;
+        };
+
+        let mut image_bytes = {
+            let slice = gpu_source.buffer.slice(..);
+
+            {
+                let (tx, rx) = oneshot::channel();
+                device.map_buffer(&slice, MapMode::Read, move |res| {
+                    tx.send(res).unwrap();
+                });
+                device.poll(Maintain::Wait);
+                rx.block_on().unwrap().unwrap();
+            }
+             
+            slice.get_mapped_range().to_vec()
+        };
+
+        gpu_source.buffer.unmap();
+
+        let bytes_per_row = gpu_source.bytes_per_row as usize;
+        let padded_bytes_per_row = gpu_source.padded_bytes_per_row as usize;
+        let source_size = gpu_source.source_size;
+        let destination_handle = destination_handle.clone();
+        let source_format = gpu_source.format;
+
+        std::thread::spawn(move || {
+            if bytes_per_row != padded_bytes_per_row {
+                let mut unpadded_bytes = Vec::<u8>::with_capacity(source_size.height as usize * bytes_per_row);
+                for padded_row in image_bytes.chunks(padded_bytes_per_row) {
+                    unpadded_bytes.extend_from_slice(&padded_row[..bytes_per_row]);
+                }
+                image_bytes = unpadded_bytes;
+            }
+
+            *destination_handle.0.lock().unwrap() = Image::new(
+                Extent3d {
+                    width: source_size.width,
+                    height: source_size.height,
+                    depth_or_array_layers: 1,
+                },
+                TextureDimension::D2,
+                image_bytes,
+                source_format,
+                RenderAssetUsages::MAIN_WORLD | RenderAssetUsages::RENDER_WORLD,
+            );
+        });
+    }
+
+}