rewrite the camera for the specific use case

src/camera.rs

@@ -1,40 +1,51 @@
-use glam::{Mat3, Vec3};
+use glam::{Vec3, vec3};
 
-pub fn ypr_to_mat(ypr: Vec3) -> Mat3 {
-	glam::Mat3::from_euler(glam::EulerRot::ZXZEx, ypr.x, ypr.y, ypr.z)
+/// A camera always directed at the origin.
+#[derive(Debug, Clone, Copy)]
+pub struct OrbitalCamera {
+	/// Horizontal position (angle), in radians from +X towards +Y.
+	pub position_yaw: f32,
+
+	/// Vertical position (angle), in radians from XY plane towards +Z.
+	pub position_pitch: f32,
+
+	/// Distance from the origin.
+	pub distance: f32,
+}
+
+impl OrbitalCamera {
+	pub fn position(&self) -> Vec3 {
+		let (y, x) = self.position_yaw.sin_cos();
+		let (z, xy) = self.position_pitch.sin_cos();
+		self.distance * vec3(xy * x, xy * y, z)
+	}
 }
 
 #[cfg(test)]
 mod tests {
-	use std::f32::consts::PI;
-
 	use approx::assert_ulps_eq;
 	use glam::vec3;
 
 	use super::*;
 
 	#[test]
-	fn test_ypr_to_mat() {
-		assert_ulps_eq!(ypr_to_mat(vec3(0., 0., 0.)), Mat3::IDENTITY, max_ulps = 3);
-		assert_ulps_eq!(
-			ypr_to_mat(vec3(PI / 2., 0., 0.)),
-			Mat3::from_cols_array_2d(&[[0., 1., 0.], [-1., 0., 0.], [0., 0., 1.]]),
-			max_ulps = 3,
-		);
-		assert_ulps_eq!(
-			ypr_to_mat(vec3(0., 0., PI / 2.)),
-			Mat3::from_cols_array_2d(&[[0., 1., 0.], [-1., 0., 0.], [0., 0., 1.]]),
-			max_ulps = 3,
-		);
-		assert_ulps_eq!(
-			ypr_to_mat(vec3(0., PI / 2., 0.)),
-			Mat3::from_cols_array_2d(&[[1., 0., 0.], [0., 0., 1.], [0., -1., 0.]]),
-			max_ulps = 3,
-		);
-		assert_ulps_eq!(
-			ypr_to_mat(vec3(PI / 2., PI / 2., 0.)),
-			Mat3::from_cols_array_2d(&[[0., 0., 1.], [-1., 0., 0.], [0., -1., 0.]]),
-			max_ulps = 3,
-		);
+	fn test_orbital_camera_position() {
+		fn camera_pos_deg(yaw: f32, pitch: f32) -> Vec3 {
+			OrbitalCamera {
+				position_yaw: yaw.to_radians(),
+				position_pitch: pitch.to_radians(),
+				distance: 1.0,
+			}
+			.position()
+		}
+		assert_ulps_eq!(camera_pos_deg(0., 0.), vec3(1., 0., 0.), max_ulps = 3);
+		assert_ulps_eq!(camera_pos_deg(90., 0.), vec3(0., 1., 0.), max_ulps = 3);
+		assert_ulps_eq!(camera_pos_deg(0., 90.), vec3(0., 0., 1.), max_ulps = 3);
+		assert_ulps_eq!(camera_pos_deg(90., 90.), vec3(0., 0., 1.), max_ulps = 3);
+
+		let s2 = 0.5f32.sqrt();
+		assert_ulps_eq!(camera_pos_deg(45., 0.), vec3(s2, s2, 0.), max_ulps = 3);
+		assert_ulps_eq!(camera_pos_deg(0., 45.), vec3(s2, 0., s2), max_ulps = 3);
+		assert_ulps_eq!(camera_pos_deg(45., 45.), vec3(0.5, 0.5, s2), max_ulps = 3);
 	}
 }