src/vram.rs

@@ -40,12 +40,10 @@ impl VramProcessor {
         &self,
         renderer: R,
     ) -> ([VramImageHandle; N], VramParams<R::Params>) {
-        let handles = renderer.sizes().map(|[width, height]| {
-            let data = Arc::new(Mutex::new(None));
-            VramImageHandle {
-                size: [width as f32, height as f32],
-                data,
-            }
+        let states = renderer.sizes().map(VramRenderImageState::new);
+        let handles = states.clone().map(|state| VramImageHandle {
+            size: state.size.map(|i| i as f32),
+            data: state.sink,
         });
         let images = renderer
             .sizes()
@@ -55,7 +53,7 @@ impl VramProcessor {
             renderer,
             params: Arc::downgrade(&sink),
             images,
-            sinks: handles.clone().map(|i| i.data),
+            states,
         }));
         let params = VramParams {
             value: R::Params::default(),
@@ -101,42 +99,35 @@ impl VramProcessorWorker {
     }
 }
 
-pub enum VramImage {
-    Unchanged(Option<Arc<ColorImage>>),
-    Changed(ColorImage),
+pub struct VramImage {
+    size: [usize; 2],
+    shades: Vec<u8>,
 }
 
 impl VramImage {
     pub fn new(width: usize, height: usize) -> Self {
-        Self::Changed(ColorImage::new([width, height], Color32::BLACK))
+        Self {
+            size: [width, height],
+            shades: vec![0; width * height],
+        }
     }
 
     pub fn write(&mut self, coords: (usize, usize), shade: u8) {
-        match self {
-            Self::Unchanged(image) => {
-                if image.as_ref().is_none_or(|i| i[coords].r() == shade) {
-                    return;
-                }
-                let Some(mut new_image) = image.take().map(Arc::unwrap_or_clone) else {
-                    return;
-                };
-                new_image[coords] = Color32::from_gray(shade);
-                *self = Self::Changed(new_image);
-            }
-            Self::Changed(image) => {
-                image[coords] = Color32::from_gray(shade);
-            }
-        }
+        self.shades[coords.1 * self.size[0] + coords.0] = shade;
     }
 
-    pub fn take(&mut self) -> Option<Arc<ColorImage>> {
-        match self {
-            Self::Unchanged(_) => None,
-            Self::Changed(image) => {
-                let arced = Arc::new(std::mem::take(image));
-                *self = Self::Unchanged(Some(arced.clone()));
-                Some(arced)
+    pub fn changed(&self, image: &ColorImage) -> bool {
+        image
+            .pixels
+            .iter()
+            .map(|p| p.r())
+            .zip(&self.shades)
+            .any(|(a, b)| a != *b)
     }
+
+    pub fn read(&self, image: &mut ColorImage) {
+        for (pixel, shade) in image.pixels.iter_mut().zip(&self.shades) {
+            *pixel = Color32::from_gray(*shade);
         }
     }
 }
@@ -181,11 +172,47 @@ pub trait VramRenderer<const N: usize>: Send {
     fn render(&mut self, params: &Self::Params, images: &mut [VramImage; N]);
 }
 
+#[derive(Clone)]
+struct VramRenderImageState {
+    size: [usize; 2],
+    buffers: [Arc<ColorImage>; 2],
+    last_buffer: usize,
+    sink: Arc<Mutex<Option<Arc<ColorImage>>>>,
+}
+
+impl VramRenderImageState {
+    fn new(size: [usize; 2]) -> Self {
+        let buffers = [
+            Arc::new(ColorImage::new(size, Color32::BLACK)),
+            Arc::new(ColorImage::new(size, Color32::BLACK)),
+        ];
+        let sink = buffers[0].clone();
+        Self {
+            size,
+            buffers,
+            last_buffer: 0,
+            sink: Arc::new(Mutex::new(Some(sink))),
+        }
+    }
+    fn try_send_update(&mut self, image: &VramImage) {
+        let last = &self.buffers[self.last_buffer];
+        if !image.changed(last) {
+            return;
+        }
+
+        let next_buffer = (self.last_buffer + 1) % self.buffers.len();
+        let next = &mut self.buffers[next_buffer];
+        image.read(Arc::make_mut(next));
+        self.last_buffer = next_buffer;
+        self.sink.lock().unwrap().replace(next.clone());
+    }
+}
+
 struct VramRendererWrapper<const N: usize, R: VramRenderer<N>> {
     renderer: R,
     params: Weak<Mutex<R::Params>>,
     images: [VramImage; N],
-    sinks: [Arc<Mutex<Option<Arc<ColorImage>>>>; N],
+    states: [VramRenderImageState; N],
 }
 
 trait VramRendererImpl: Send {
@@ -203,10 +230,8 @@ impl<const N: usize, R: VramRenderer<N> + Send> VramRendererImpl for VramRendere
         };
         self.renderer.render(&params, &mut self.images);
 
-        for (image, sink) in self.images.iter_mut().zip(&self.sinks) {
-            if let Some(update) = image.take() {
-                sink.lock().unwrap().replace(update);
-            }
+        for (state, image) in self.states.iter_mut().zip(&self.images) {
+            state.try_send_update(image);
         }
         Ok(())
     }