finished phase 2a

src/render.rs

@@ -0,0 +1,64 @@
+use crate::palette::index_to_rgb;
+
+pub trait Renderer {
+    fn present(&mut self, framebuffer: &[u8], width: u16, height: u16);
+}
+
+pub struct PpmRenderer {
+    dir: String,
+    frame: u32,
+}
+
+
+impl PpmRenderer {
+    pub fn new(dir: &str) -> Self {
+        Self { dir: dir.to_string(), frame: 0 }
+    }
+}
+
+
+impl Renderer for PpmRenderer {
+    fn present(&mut self, framebuffer: &[u8], width: u16, height: u16) {
+        std::fs::create_dir_all(&self.dir).expect("failed to create render dir");
+        let path = format!("{}/frame_{:04}.ppm", self.dir, self.frame);
+        std::fs::write(&path, ppm_bytes(framebuffer, width, height))
+            .expect("failed to write PPM file");
+        self.frame += 1;
+    }
+}
+
+pub fn ppm_bytes(framebuffer: &[u8], width: u16, height: u16) -> Vec<u8> {
+    let mut out = format!("P6\n{width} {height}\n255\n").into_bytes();
+    for &idx in framebuffer {
+        let (r, g, b) = index_to_rgb(idx);
+        out.extend_from_slice(&[r, g, b]);
+    }
+    out
+}
+
+// Tests
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ppm_bytes_has_correct_header() {
+        let fb = [0u8; 4];
+        let bytes = ppm_bytes(&fb, 2, 2);
+        let expected_header = "P6\n2 2\n255\n";
+        let got = String::from_utf8_lossy(&bytes[..expected_header.len()]);
+        assert_eq!(got, expected_header);
+    }
+
+    #[test]
+    fn ppm_bytes_emits_rgb_per_pixel() {
+        let fb = [0x21u8, 0x21, 0x00, 0x3F];   // 4 pixels: 2x2
+        let bytes = ppm_bytes(&fb, 2, 2);
+        let header = format!("P6\n2 2\n255\n");
+        let pixels = &bytes[header.len()..];
+        assert_eq!(pixels.len(), 2 * 2 * 3);   // 12 RGB bytes
+
+        assert_eq!(&pixels[0..3], &[0x64, 0x8D, 0xFF]);   // pixel 0 = 0x21, unchanged
+        assert_eq!(&pixels[9..12], &[0x66, 0x87, 0x96]);  // pixel 3 = 0x3F  (was 6..9)
+    }
+}