fix janky lines

Turns out there was a small copy-and-paste error that caused the
polygons to not line up with the circles.

The other change doesn't impact line rendering, but ensures that we stay
in u64 territory as much as possible to avoid floating point
imprecisions if the integers do get too big.

1 files changed, 17 insertions, 4 deletions

diff --git a/src/renderer.rs b/src/renderer.rs
index 14dfb6f..c523268 100644
--- a/src/renderer.rs
+++ b/src/renderer.rs
@@ -38,6 +38,20 @@ fn render_circle<P: Pixel>(layer: &mut TileLayer<P>, center: (u64, u64), radius:
     }
 }
 
+fn direction_vector(a: (u64, u64), b: (u64, u64)) -> Vector2<f64> {
+    let dx = if b.0 > a.0 {
+        (b.0 - a.0) as f64
+    } else {
+        -((a.0 - b.0) as f64)
+    };
+    let dy = if b.1 > a.1 {
+        (b.1 - a.1) as f64
+    } else {
+        -((a.1 - b.1) as f64)
+    };
+    vector![dx, dy]
+}
+
 fn render_line<P: Pixel>(
     layer: &mut TileLayer<P>,
     start: (u64, u64),
@@ -58,16 +72,15 @@ fn render_line<P: Pixel>(
             a[0] + b[0] as u64
         };
         let y = if b[1] < 0 {
-            a[1] - b[0].abs() as u64
+            a[1] - b[1].abs() as u64
         } else {
             a[1] + b[1] as u64
         };
         vector![x, y]
     }
 
-    let r = vector![end.0 as f64, end.1 as f64] - vector![start.0 as f64, start.1 as f64];
-    let r = r.normalize();
-    let normal = vector![r[1], -r[0]];
+    let r = direction_vector(start, end);
+    let normal = vector![r[1], -r[0]].normalize();
 
     let start = vector![start.0, start.1];
     let end = vector![end.0, end.1];