2 files changed, 132 insertions, 0 deletions

diff --git a/rspaint/Cargo.toml b/rspaint/Cargo.toml
new file mode 100644
index 0000000..66364a2
--- /dev/null
+++ b/rspaint/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "rspaint"
+version = "0.1.0"
+edition = "2024"
+
+[lints]
+workspace = true
+
+[dependencies]
+rsnix = { path = "../rsnix" }
diff --git a/rspaint/src/lib.rs b/rspaint/src/lib.rs
new file mode 100644
index 0000000..7c2e2d2
--- /dev/null
+++ b/rspaint/src/lib.rs
@@ -0,0 +1,122 @@
+#![no_std]
+
+//! Paint — the first GUI app: a freehand pen on a raster canvas.
+
+use rsnix::ps2::{KeyEvent, MouseKind};
+use rsnix::{sched, wm};
+
+const W: usize = 640;
+const H: usize = 480;
+
+/// 8-colour palette selected by keys 1–8.
+const PALETTE: [(u8, u8, u8); 8] = [
+    (255, 255, 255), // 1 white
+    (0, 0, 0),       // 2 black
+    (170, 0, 0),     // 3 red
+    (0, 170, 0),     // 4 green
+    (0, 0, 170),     // 5 blue
+    (170, 170, 0),   // 6 yellow
+    (0, 170, 170),   // 7 cyan
+    (170, 0, 170),   // 8 magenta
+];
+
+/// Run the paint program as a spawned task: create a window, then loop on
+/// events (pen strokes from the mouse, colour/clear from keys) until `Close`.
+pub fn run() {
+    let Some(id) = wm::create_window("paint", W, H) else {
+        return;
+    };
+    let Some((buf, _, _)) = wm::buffer(id) else {
+        return;
+    };
+
+    let mut color: usize = 0; // white
+    let mut last: Option<(i32, i32)> = None;
+
+    loop {
+        match sched::recv_blocking() {
+            sched::TaskMsg::Close => break,
+            sched::TaskMsg::AppMouse(m) => match m.kind {
+                MouseKind::Press => {
+                    plot(buf, m.x, m.y, color);
+                    last = Some((m.x, m.y));
+                    wm::flush(id);
+                }
+                MouseKind::Move => {
+                    if m.buttons & 1 != 0 {
+                        if let Some((lx, ly)) = last {
+                            line(buf, lx, ly, m.x, m.y, color);
+                            wm::flush(id);
+                        }
+                    }
+                    last = Some((m.x, m.y));
+                }
+                MouseKind::Release => {
+                    last = None;
+                }
+            },
+            sched::TaskMsg::Key(k) => {
+                if let KeyEvent::Char(c) = k {
+                    match c {
+                        '1'..='8' => color = (c as u8 - b'1') as usize,
+                        'c' => {
+                            fill(buf, 1); // clear to black
+                            wm::flush(id);
+                        }
+                        _ => {}
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+    wm::destroy(id);
+}
+
+fn pack(idx: usize) -> u32 {
+    let (r, g, b) = PALETTE[idx.min(PALETTE.len() - 1)];
+    rsnix::gop::rgb(r, g, b)
+}
+
+fn plot(buf: *mut u32, x: i32, y: i32, color: usize) {
+    if x < 0 || y < 0 || x >= W as i32 || y >= H as i32 {
+        return;
+    }
+    unsafe {
+        *buf.add(y as usize * W + x as usize) = pack(color);
+    }
+}
+
+/// Bresenham line between two points.
+fn line(buf: *mut u32, x0: i32, y0: i32, x1: i32, y1: i32, color: usize) {
+    let mut x = x0;
+    let mut y = y0;
+    let dx = (x1 - x0).abs();
+    let sx = if x0 < x1 { 1 } else { -1 };
+    let dy = -(y1 - y0).abs();
+    let sy = if y0 < y1 { 1 } else { -1 };
+    let mut err = dx + dy;
+    loop {
+        plot(buf, x, y, color);
+        if x == x1 && y == y1 {
+            break;
+        }
+        let e2 = 2 * err;
+        if e2 >= dy {
+            err += dy;
+            x += sx;
+        }
+        if e2 <= dx {
+            err += dx;
+            y += sy;
+        }
+    }
+}
+
+fn fill(buf: *mut u32, color: usize) {
+    unsafe {
+        for i in 0..(W * H) {
+            *buf.add(i) = pack(color);
+        }
+    }
+}