perf: fast display (row runs, bulk fills, pixel scroll), terminal draws changed cells only + scrolls pixels, print! batched (was IPC per fmt fragment), snake sleeps on timer

crates/drivers/framebuffer/virtio/src/lib.rs

@@ -15,6 +15,8 @@ const VQUEUE_VA: VirtualAddress = VirtualAddress::from_raw(0x21000);
 const CMDBUF_VA: VirtualAddress = VirtualAddress::from_raw(0x23000);
 const FB_VA: VirtualAddress = VirtualAddress::from_raw(0x100000);
 const FB_BPP: usize = 4;
+/// Pixels converted and stored per run.
+const RUN: usize = 64;
 const RESOURCE_ID: u32 = 1;
 /// When the device will not say.
 const DEFAULT_SIZE: (u16, u16) = (640, 480);
@@ -79,6 +81,12 @@ impl VirtioFramebuffer {
     }
 }
 
+impl VirtioFramebuffer {
+    fn pixel(&self, x: usize, y: usize) -> ByteOffset {
+        ByteOffset::new(y * self.stride + x * FB_BPP)
+    }
+}
+
 impl Framebuffer for VirtioFramebuffer {
     fn width(&self) -> Dimension {
         self.width
@@ -89,18 +97,33 @@ impl Framebuffer for VirtioFramebuffer {
     }
 
     fn write_pixel(&mut self, x: ScreenCoord, y: ScreenCoord, color: Color) {
-        if x.raw() >= self.width.raw() || y.raw() >= self.height.raw() {
-            return;
-        }
-        let offset = (y.raw() as usize) * self.stride + (x.raw() as usize) * FB_BPP;
-        self.pixels.write(ByteOffset::new(offset), color.raw());
+        self.write_row(x, y, &[color]);
     }
 
-    fn fill_rect(&mut self, x: ScreenCoord, y: ScreenCoord, w: Dimension, h: Dimension, color: Color) {
-        for dy in 0..h.raw() {
-            for dx in 0..w.raw() {
-                self.write_pixel(ScreenCoord::new(x.raw() + dx), ScreenCoord::new(y.raw() + dy), color);
+    fn write_row(&mut self, x: ScreenCoord, y: ScreenCoord, pixels: &[Color]) {
+        let (w, h) = (self.width.raw() as usize, self.height.raw() as usize);
+        let (x, y) = (x.raw() as usize, y.raw() as usize);
+        if x >= w || y >= h {
+            return;
+        }
+        let mut run = [0u32; RUN];
+        let mut at = self.pixel(x, y);
+        for chunk in pixels[..pixels.len().min(w - x)].chunks(RUN) {
+            for (slot, c) in run.iter_mut().zip(chunk) {
+                *slot = c.raw();
             }
+            self.pixels.write_u32s(at, &run[..chunk.len()]);
+            at = at + chunk.len() * FB_BPP;
+        }
+    }
+
+    /// Callers clip to the screen (the display server does).
+    fn fill_rect(&mut self, x: ScreenCoord, y: ScreenCoord, w: Dimension, h: Dimension, color: Color) {
+        let (fw, fh) = (self.width.raw() as usize, self.height.raw() as usize);
+        let (x, y) = (x.raw() as usize, y.raw() as usize);
+        let w = (w.raw() as usize).min(fw.saturating_sub(x));
+        for row in y..(y + h.raw() as usize).min(fh) {
+            self.pixels.fill_u32(self.pixel(x, row), w, color.raw());
         }
     }
 
@@ -109,6 +132,17 @@ impl Framebuffer for VirtioFramebuffer {
         self.pixels.fill_u32(ByteOffset::ZERO, total, color.raw());
     }
 
+    fn scroll_up(&mut self, top: ScreenCoord, height: Dimension, by: Dimension, fill: Color) {
+        let fh = self.height.raw() as usize;
+        let top = top.raw() as usize;
+        let bottom = (top + height.raw() as usize).min(fh);
+        let by = (by.raw() as usize).min(bottom.saturating_sub(top));
+        let moved = bottom - top - by;
+        self.pixels.copy_within(self.pixel(0, top + by), self.pixel(0, top), moved * self.stride);
+        let width = self.width.raw() as usize;
+        self.pixels.fill_u32(self.pixel(0, bottom - by), by * width, fill.raw());
+    }
+
     fn flush(&mut self) {
         let w = self.width.raw() as u32;
         let h = self.height.raw() as u32;