1 files changed, 123 insertions, 0 deletions
diff --git a/src/rasterizer/line.rs b/src/rasterizer/line.rs
new file mode 100644
index 0000000..0f24b0a
--- /dev/null
+++ b/src/rasterizer/line.rs
@@ -0,0 +1,123 @@
+use crate::{BackendCoord, BackendStyle, DrawingBackend, DrawingErrorKind};
+
+pub fn draw_line<DB: DrawingBackend, S: BackendStyle>(
+    back: &mut DB,
+    mut from: BackendCoord,
+    mut to: BackendCoord,
+    style: &S,
+) -> Result<(), DrawingErrorKind<DB::ErrorType>> {
+    if style.color().alpha == 0.0 {
+        return Ok(());
+    }
+
+    if style.stroke_width() != 1 {
+        // If the line is wider than 1px, then we need to make it a polygon
+        let v = (i64::from(to.0 - from.0), i64::from(to.1 - from.1));
+        let l = ((v.0 * v.0 + v.1 * v.1) as f64).sqrt();
+
+        if l < 1e-5 {
+            return Ok(());
+        }
+
+        let v = (v.0 as f64 / l, v.1 as f64 / l);
+
+        let r = f64::from(style.stroke_width()) / 2.0;
+        let mut trans = [(v.1 * r, -v.0 * r), (-v.1 * r, v.0 * r)];
+        let mut vertices = vec![];
+
+        for point in [from, to].iter() {
+            for t in trans.iter() {
+                vertices.push((
+                    (f64::from(point.0) + t.0) as i32,
+                    (f64::from(point.1) + t.1) as i32,
+                ))
+            }
+
+            trans.swap(0, 1);
+        }
+
+        return back.fill_polygon(vertices, style);
+    }
+
+    if from.0 == to.0 {
+        if from.1 > to.1 {
+            std::mem::swap(&mut from, &mut to);
+        }
+        for y in from.1..=to.1 {
+            check_result!(back.draw_pixel((from.0, y), style.color()));
+        }
+        return Ok(());
+    }
+
+    if from.1 == to.1 {
+        if from.0 > to.0 {
+            std::mem::swap(&mut from, &mut to);
+        }
+        for x in from.0..=to.0 {
+            check_result!(back.draw_pixel((x, from.1), style.color()));
+        }
+        return Ok(());
+    }
+
+    let steep = (from.0 - to.0).abs() < (from.1 - to.1).abs();
+
+    if steep {
+        from = (from.1, from.0);
+        to = (to.1, to.0);
+    }
+
+    let (from, to) = if from.0 > to.0 {
+        (to, from)
+    } else {
+        (from, to)
+    };
+
+    let mut size_limit = back.get_size();
+
+    if steep {
+        size_limit = (size_limit.1, size_limit.0);
+    }
+
+    let grad = f64::from(to.1 - from.1) / f64::from(to.0 - from.0);
+
+    let mut put_pixel = |(x, y): BackendCoord, b: f64| {
+        if steep {
+            back.draw_pixel((y, x), style.color().mix(b))
+        } else {
+            back.draw_pixel((x, y), style.color().mix(b))
+        }
+    };
+
+    let y_step_limit =
+        (f64::from(to.1.min(size_limit.1 as i32 - 1).max(0) - from.1) / grad).floor() as i32;
+
+    let batch_start = (f64::from(from.1.min(size_limit.1 as i32 - 2).max(0) - from.1) / grad)
+        .abs()
+        .ceil() as i32
+        + from.0;
+
+    let batch_limit =
+        to.0.min(size_limit.0 as i32 - 2)
+            .min(from.0 + y_step_limit - 1);
+
+    let mut y = f64::from(from.1) + f64::from(batch_start - from.0) * grad;
+
+    for x in batch_start..=batch_limit {
+        check_result!(put_pixel((x, y as i32), 1.0 + y.floor() - y));
+        check_result!(put_pixel((x, y as i32 + 1), y - y.floor()));
+
+        y += grad;
+    }
+
+    if to.0 >= batch_limit + 1 && y < f64::from(to.1) {
+        let x = batch_limit as i32 + 1;
+        if 1.0 + y.floor() - y > 1e-5 {
+            check_result!(put_pixel((x, y as i32), 1.0 + y.floor() - y));
+        }
+        if y - y.floor() > 1e-5 && y + 1.0 < f64::from(to.1) {
+            check_result!(put_pixel((x, y as i32 + 1), y - y.floor()));
+        }
+    }
+
+    Ok(())
+}