feat(engine): make camera look at a target position

1 files changed, 35 insertions, 0 deletions

diff --git a/engine/src/matrix.rs b/engine/src/matrix.rs
index c060b59..85a3721 100644
--- a/engine/src/matrix.rs
+++ b/engine/src/matrix.rs
@@ -71,4 +71,39 @@ impl Matrix<f32, 4, 4>
         self.set_cell(2, 2, scaling.z);
         self.set_cell(3, 3, 1.0);
     }
+
+    pub fn look_at(&mut self, eye: &Vec3<f32>, target: &Vec3<f32>, up: &Vec3<f32>)
+    {
+        let rev_target_direction = (eye - target).normalize();
+
+        let camera_right = up.cross(&rev_target_direction).normalize();
+
+        let camera_up = rev_target_direction.cross(&camera_right);
+
+        self.set_cell(0, 0, camera_right.x);
+        self.set_cell(0, 1, camera_right.y);
+        self.set_cell(0, 2, camera_right.z);
+
+        self.set_cell(1, 0, camera_up.x);
+        self.set_cell(1, 1, camera_up.y);
+        self.set_cell(1, 2, camera_up.z);
+
+        self.set_cell(2, 0, rev_target_direction.x);
+        self.set_cell(2, 1, rev_target_direction.y);
+        self.set_cell(2, 2, rev_target_direction.z);
+
+        // The vector is negated since we want the world to be translated in the opposite
+        // direction of where we want the camera to move.
+        let camera_pos = -Vec3 {
+            x: camera_right.dot(eye),
+            y: camera_up.dot(eye),
+            z: rev_target_direction.dot(eye),
+        };
+
+        self.set_cell(0, 3, camera_pos.x);
+        self.set_cell(1, 3, camera_pos.y);
+        self.set_cell(2, 3, camera_pos.z);
+
+        self.set_cell(3, 3, 1.0);
+    }
 }