convert between origin units

crates/servicepoint/src/origin.rs

@@ -1,3 +1,4 @@
+use crate::TILE_SIZE;
 use std::marker::PhantomData;
 
 /// An origin marks the top left position of a window sent to the display.
@@ -46,3 +47,69 @@ pub struct Tiles();
 impl DisplayUnit for Pixels {}
 
 impl DisplayUnit for Tiles {}
+
+impl From<&Origin<Tiles>> for Origin<Pixels> {
+    fn from(value: &Origin<Tiles>) -> Self {
+        Self {
+            x: value.x * TILE_SIZE,
+            y: value.y * TILE_SIZE,
+            phantom_data: PhantomData,
+        }
+    }
+}
+
+impl TryFrom<&Origin<Pixels>> for Origin<Tiles> {
+    type Error = ();
+
+    fn try_from(value: &Origin<Pixels>) -> Result<Self, Self::Error> {
+        let (x, x_rem) = (value.x / TILE_SIZE, value.x % TILE_SIZE);
+        if x_rem != 0 {
+            return Err(());
+        }
+        let (y, y_rem) = (value.y / TILE_SIZE, value.y % TILE_SIZE);
+        if y_rem != 0 {
+            return Err(());
+        }
+
+        Ok(Self {
+            x,
+            y,
+            phantom_data: PhantomData,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn origin_tile_to_pixel() {
+        let tile: Origin<Tiles> = Origin::new(1, 2);
+        let actual: Origin<Pixels> = Origin::from(&tile);
+        let expected: Origin<Pixels> = Origin::new(8, 16);
+        assert_eq!(actual, expected);
+    }
+
+    #[test]
+    fn origin_pixel_to_tile() {
+        let pixel: Origin<Pixels> = Origin::new(8, 16);
+        let actual: Origin<Tiles> = Origin::try_from(&pixel).unwrap();
+        let expected: Origin<Tiles> = Origin::new(1, 2);
+        assert_eq!(actual, expected);
+    }
+
+    #[test]
+    #[should_panic]
+    fn origin_pixel_to_tile_fail_y() {
+        let pixel: Origin<Pixels> = Origin::new(8, 15);
+        let _: Origin<Tiles> = Origin::try_from(&pixel).unwrap();
+    }
+
+    #[test]
+    #[should_panic]
+    fn origin_pixel_to_tile_fail_x() {
+        let pixel: Origin<Pixels> = Origin::new(7, 16);
+        let _: Origin<Tiles> = Origin::try_from(&pixel).unwrap();
+    }
+}