implement phase 5~7

src/projection.rs

@@ -0,0 +1,77 @@
+use eframe::egui;
+
+pub trait MapProjection: Send + Sync {
+    fn project(&self, lon: f64, lat: f64, rect: egui::Rect) -> egui::Pos2;
+    fn unproject(&self, pos: egui::Pos2, rect: egui::Rect) -> (f64, f64);
+    fn name(&self) -> &'static str;
+}
+
+pub struct Equirectangular;
+
+impl MapProjection for Equirectangular {
+    fn project(&self, lon: f64, lat: f64, rect: egui::Rect) -> egui::Pos2 {
+        egui::pos2(
+            rect.left() + ((lon + 180.0) / 360.0) as f32 * rect.width(),
+            rect.top() + ((90.0 - lat) / 180.0) as f32 * rect.height(),
+        )
+    }
+
+    fn unproject(&self, pos: egui::Pos2, rect: egui::Rect) -> (f64, f64) {
+        let lon = (pos.x - rect.left()) as f64 / rect.width() as f64 * 360.0 - 180.0;
+        let lat = 90.0 - (pos.y - rect.top()) as f64 / rect.height() as f64 * 180.0;
+        (lon, lat)
+    }
+
+    fn name(&self) -> &'static str {
+        "Equirectangular"
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn unit_rect() -> egui::Rect {
+        egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(360.0, 180.0))
+    }
+
+    #[test]
+    fn roundtrip_center() {
+        let proj = Equirectangular;
+        let r = unit_rect();
+        let pos = proj.project(0.0, 0.0, r);
+        let (lon, lat) = proj.unproject(pos, r);
+        assert!((lon).abs() < 1e-4);
+        assert!((lat).abs() < 1e-4);
+    }
+
+    #[test]
+    fn roundtrip_corners() {
+        let proj = Equirectangular;
+        let r = unit_rect();
+        for (lon, lat) in [(-180.0_f64, 90.0_f64), (180.0, -90.0), (-180.0, -90.0), (180.0, 90.0)] {
+            let pos = proj.project(lon, lat, r);
+            let (lon2, lat2) = proj.unproject(pos, r);
+            assert!((lon - lon2).abs() < 1e-4, "lon {lon} → {lon2}");
+            assert!((lat - lat2).abs() < 1e-4, "lat {lat} → {lat2}");
+        }
+    }
+
+    #[test]
+    fn project_prime_meridian_equator() {
+        let proj = Equirectangular;
+        let r = unit_rect();
+        let pos = proj.project(0.0, 0.0, r);
+        assert!((pos.x - 180.0).abs() < 1e-3, "x={}", pos.x);
+        assert!((pos.y - 90.0).abs() < 1e-3, "y={}", pos.y);
+    }
+
+    #[test]
+    fn rect_scaling() {
+        let proj = Equirectangular;
+        let r = egui::Rect::from_min_size(egui::pos2(10.0, 20.0), egui::vec2(720.0, 360.0));
+        let pos = proj.project(0.0, 0.0, r);
+        assert!((pos.x - 370.0).abs() < 1e-3, "x={}", pos.x);
+        assert!((pos.y - 200.0).abs() < 1e-3, "y={}", pos.y);
+    }
+}