Save inverse projection matrix for speed

scottshambaugh · scottshambaugh · commit 6745c1bade2f · 2023-02-23T19:29:45.000-07:00
diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -157,6 +157,7 @@ def __init__(
         # Enable drawing of axes by Axes3D class
         self.set_axis_on()
         self.M = None
+        self.invM = None
 
         # func used to format z -- fall back on major formatters
         self.fmt_zdata = None
@@ -456,6 +457,7 @@ def draw(self, renderer):
 
         # add the projection matrix to the renderer
         self.M = self.get_proj()
+        self.invM = np.linalg.inv(self.M)
 
         collections_and_patches = (
             artist for artist in self._children
@@ -1109,7 +1111,7 @@ def _calc_coord(self, xv, yv, renderer=None):
             zv = -1 / self._focal_length
 
         # Convert point on view plane to data coordinates
-        p1 = np.array(proj3d.inv_transform(xv, yv, zv, self.M)).ravel()
+        p1 = np.array(proj3d.inv_transform(xv, yv, zv, self.invM)).ravel()
 
         # Get the vector from the camera to the point on the view plane
         vec = self._get_camera_loc() - p1
diff --git a/lib/mpl_toolkits/mplot3d/proj3d.py b/lib/mpl_toolkits/mplot3d/proj3d.py
@@ -190,13 +190,12 @@ def _proj_transform_vec_clip(vec, M):
     return txs, tys, tzs, tis
 
 
-def inv_transform(xs, ys, zs, M):
+def inv_transform(xs, ys, zs, invM):
     """
-    Transform the points by the inverse of the projection matrix *M*.
+    Transform the points by the inverse of the projection matrix, `invM`.
     """
-    iM = linalg.inv(M)
     vec = _vec_pad_ones(xs, ys, zs)
-    vecr = np.dot(iM, vec)
+    vecr = np.dot(invM, vec)
     if vecr.shape == (4,):
         vecr = vecr.reshape((4, 1))
     for i in range(vecr.shape[1]):
diff --git a/lib/mpl_toolkits/mplot3d/tests/test_axes3d.py b/lib/mpl_toolkits/mplot3d/tests/test_axes3d.py
@@ -1023,13 +1023,14 @@ def _test_proj_make_M():
 
 def test_proj_transform():
     M = _test_proj_make_M()
+    invM = np.linalg.inv(M)
 
     xs = np.array([0, 1, 1, 0, 0, 0, 1, 1, 0, 0]) * 300.0
     ys = np.array([0, 0, 1, 1, 0, 0, 0, 1, 1, 0]) * 300.0
     zs = np.array([0, 0, 0, 0, 0, 1, 1, 1, 1, 1]) * 300.0
 
     txs, tys, tzs = proj3d.proj_transform(xs, ys, zs, M)
-    ixs, iys, izs = proj3d.inv_transform(txs, tys, tzs, M)
+    ixs, iys, izs = proj3d.inv_transform(txs, tys, tzs, invM)
 
     np.testing.assert_almost_equal(ixs, xs)
     np.testing.assert_almost_equal(iys, ys)
