From 424db4b3e492a5a9e51c8b62b75ded2f6ef9b1cb Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Tue, 31 Jan 2023 12:20:25 -0800
Subject: [PATCH] Ensure view matrix is not computed more than it needs to be

---
 manimlib/camera/camera_frame.py | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/manimlib/camera/camera_frame.py b/manimlib/camera/camera_frame.py
index 9c01af73..e0bc120b 100644
--- a/manimlib/camera/camera_frame.py
+++ b/manimlib/camera/camera_frame.py
@@ -29,6 +29,9 @@ class CameraFrame(Mobject):
     ):
         super().__init__(**kwargs)
 
+        self.uniforms["orientation"] = Rotation.identity().as_quat()
+        self.uniforms["fovy"] = fovy
+
         self.view_matrix = np.identity(4)
         self.default_orientation = Rotation.identity()
 
@@ -36,8 +39,10 @@ class CameraFrame(Mobject):
         self.set_width(frame_shape[0], stretch=True)
         self.set_height(frame_shape[1], stretch=True)
         self.move_to(center_point)
-        self.uniforms["orientation"] = Rotation.identity().as_quat()
-        self.uniforms["fovy"] = fovy
+
+    def note_changed_data(self, recurse_up: bool = True):
+        super().note_changed_data(recurse_up)
+        self.get_view_matrix(refresh=True)
 
     def set_orientation(self, rotation: Rotation):
         self.uniforms["orientation"][:] = rotation.as_quat()
@@ -77,20 +82,32 @@ class CameraFrame(Mobject):
     def get_inverse_camera_rotation_matrix(self):
         return self.get_orientation().as_matrix().T
 
-    def get_view_matrix(self):
+    def get_view_matrix(self, refresh=False):
         """
         Returns a 4x4 for the affine transformation mapping a point
         into the camera's internal coordinate system
         """
-        shift = Matrix44.from_translation(-self.get_center()).T
-        rotation = Matrix44.from_quaternion(self.uniforms["orientation"]).T
-        scale = Matrix44(np.identity(3) / self.get_scale())
-        self.view_matrix[:] = shift * rotation * scale
+        if refresh:
+            shift = np.identity(4)
+            rotation = np.identity(4)
+            scale = np.identity(4)
+
+            shift[:3, 3] = -self.get_center()
+            rotation[:3, :3] = self.get_inverse_camera_rotation_matrix()
+            scale[:3, :3] /= self.get_scale()
+
+            self.view_matrix = np.dot(scale, np.dot(rotation, shift))
+
         return self.view_matrix
 
     def get_inv_view_matrix(self):
         return np.linalg.inv(self.get_view_matrix())
 
+    def interpolate(self, *args, **kwargs):
+        super().interpolate(*args, **kwargs)
+        self.get_view_matrix(refresh=True)
+
+    @Mobject.affects_data
     def rotate(self, angle: float, axis: np.ndarray = OUT, **kwargs):
         rot = Rotation.from_rotvec(angle * normalize(axis))
         self.set_orientation(rot * self.get_orientation())