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/servers/display-server/src/protocol.rs

@@ -9,6 +9,9 @@ pub enum DisplayRequest {
     Flush,
     GetDimensions,
     DrawText(Text),
+    /// Moves the rows from `top`, `height` tall, up by `by`; the rows left
+    /// at the bottom are filled with `fill`.
+    Scroll { top: ScreenCoord, height: Dimension, by: Dimension, fill: Color },
 }
 
 #[derive(Debug, PartialEq)]
@@ -30,6 +33,10 @@ impl Encode for DisplayRequest {
             DisplayRequest::Flush => [2, 0, 0, 0],
             DisplayRequest::GetDimensions => [3, 0, 0, 0],
             DisplayRequest::DrawText(t) => t.words(),
+            DisplayRequest::Scroll { top, height, by, fill } => {
+                let band = (top.raw() as usize) | ((height.raw() as usize) << 16);
+                [types::display::SCROLL, band, by.raw() as usize, fill.raw() as usize]
+            }
         }
     }
 }
@@ -48,6 +55,12 @@ impl Decode for DisplayRequest {
             1 => Some(DisplayRequest::Clear { color: Color::from_raw(words[1] as u32) }),
             2 => Some(DisplayRequest::Flush),
             3 => Some(DisplayRequest::GetDimensions),
+            types::display::SCROLL => Some(DisplayRequest::Scroll {
+                top: ScreenCoord::new((words[1] & 0xFFFF) as u16),
+                height: Dimension::new(((words[1] >> 16) & 0xFFFF) as u16),
+                by: Dimension::new((words[2] & 0xFFFF) as u16),
+                fill: Color::from_raw(words[3] as u32),
+            }),
             _ => Text::from_words(words).map(DisplayRequest::DrawText),
         }
     }

crates/servers/display-server/src/server.rs

@@ -3,7 +3,7 @@ use types::bounded::CapSlot;
 
 use crate::protocol::{DisplayRequest, DisplayResponse};
 use port_framebuffer::Framebuffer;
-use types::display::text::Text;
+use types::display::text::{TEXT_BYTES, Text};
 use types::display::{Dimension, ScreenCoord};
 
 use crate::focus::Focus;
@@ -38,17 +38,20 @@ impl<F: Framebuffer> DisplayServer<F> {
         if y0.saturating_add(font::HEIGHT) > fh {
             return;
         }
-        for (i, c) in t.chars().iter().enumerate() {
-            let Some(cx) = x0.checked_add(i as u16 * font::WIDTH).filter(|cx| cx + font::WIDTH <= fw) else {
-                return;
-            };
-            for (row, bits) in font::glyph(*c).iter().enumerate() {
-                for col in 0..font::WIDTH {
-                    let on = bits & (0x80 >> col) != 0;
-                    let (x, y) = (ScreenCoord::new(cx + col), ScreenCoord::new(y0 + row as u16));
-                    self.fb.write_pixel(x, y, if on { t.fg } else { t.bg });
+        // Whole cells only.
+        let fit = (fw.saturating_sub(x0) / font::WIDTH) as usize;
+        let chars = &t.chars()[..t.chars().len().min(fit)];
+        // One run per pixel row across every cell, not a call per pixel.
+        let mut line = [t.bg; TEXT_BYTES * font::WIDTH as usize];
+        let line = &mut line[..chars.len() * font::WIDTH as usize];
+        for row in 0..font::HEIGHT {
+            for (cell, c) in line.chunks_mut(font::WIDTH as usize).zip(chars) {
+                let bits = font::glyph(*c)[row as usize];
+                for (col, px) in cell.iter_mut().enumerate() {
+                    *px = if bits & (0x80 >> col) != 0 { t.fg } else { t.bg };
                 }
             }
+            self.fb.write_row(t.x, ScreenCoord::new(y0 + row), line);
         }
     }
 }
@@ -112,6 +115,16 @@ impl<F: Framebuffer> Server for DisplayServer<F> {
                 self.fb.flush();
                 DisplayResponse::Ok
             }
+            DisplayRequest::Scroll { top, height, by, fill } => {
+                // Clipped like a rectangle: only rows on the screen move.
+                let fh = self.fb.height().raw();
+                if top.raw() < fh {
+                    let height = Dimension::new(height.raw().min(fh - top.raw()));
+                    let by = Dimension::new(by.raw().min(height.raw()));
+                    self.fb.scroll_up(top, height, by, fill);
+                }
+                DisplayResponse::Ok
+            }
             DisplayRequest::DrawText(t) => {
                 self.draw_text(&t);
                 DisplayResponse::Ok

crates/servers/display-server/src/tests/protocol.rs

@@ -53,3 +53,14 @@ fn dimensions_response_roundtrip() {
 fn invalid_request_returns_none() {
     assert!(DisplayRequest::decode([99, 0, 0, 0]).is_none());
 }
+
+#[test]
+fn scroll_roundtrip() {
+    let req = DisplayRequest::Scroll {
+        top: ScreenCoord::new(0),
+        height: Dimension::new(800),
+        by: Dimension::new(16),
+        fill: Color::from_raw(0x101018),
+    };
+    assert_eq!(DisplayRequest::decode(req.encode()), Some(req));
+}

crates/servers/display-server/src/tests/server.rs

@@ -167,3 +167,18 @@ fn text_past_the_edge_is_cut_not_wrapped() {
     server.handle(DisplayRequest::DrawText(low));
     assert_eq!(server.framebuffer().pixel_count(), 256);
 }
+
+#[test]
+fn a_scroll_off_the_screen_moves_nothing() {
+    let mut s = test_server();
+    let scroll = |top| DisplayRequest::Scroll {
+        top: ScreenCoord::new(top),
+        height: Dimension::new(u16::MAX),
+        by: Dimension::new(u16::MAX),
+        fill: Color::from_raw(0),
+    };
+    s.handle(scroll(u16::MAX));
+    assert_eq!(s.framebuffer().scrolls(), 0);
+    s.handle(scroll(0));
+    assert_eq!(s.framebuffer().scrolls(), 1, "clipped, then done");
+}