added a line drawing algorithm

will be needed to make it a bit more accurate than just 8 directions.

src/line_drawing.rs

@@ -0,0 +1,42 @@
+use core::{iter::Iterator, mem::swap};
+
+struct Point {
+    x: isize,
+    y: isize,
+}
+
+
+
+fn draw_line(mut p0: Point, mut p1: Point, matrix: &mut [[u8; 5]; 5]) {
+    let steep = (p0.x - p1.x).abs() < (p0.y - p1.x).abs();
+
+    if steep {
+        swap(&mut p0.x, &mut p0.y);
+        swap(&mut p1.x, &mut p1.y);
+    }
+
+    if p0.x > p1.x {
+        swap(&mut p0, &mut p1)
+    }
+
+    let dx = p1.x - p0.x;
+    let dy = p1.y - p0.y;
+    let derror2 = dy.abs() * 2;
+    let mut error2 = 0;
+    let mut y = p0.y;
+
+    for x in p0.x..=p1.x {
+        if steep {
+            matrix[y as usize][x as usize] = 1;
+        } else {
+            matrix[x as usize][y as usize] = 1;
+        }
+
+        error2 += derror2;
+
+        if error2 > dx {
+            y += if p1.y > p0.y { 1 } else { -1 };
+            error2 -= dx * 2
+        }
+    }
+}

src/main.rs

@@ -16,6 +16,7 @@ use rtt_target::{rprintln, rtt_init_print};
 mod calibration;
 mod led;
 mod tilt_compensation;
+mod line_drawing;
 
 use microbit::{display::blocking::Display, hal::Timer};