OpenGLVMobject fix pointwise_become_partial to fix stroke rendering (#2714)

* fix(get_nth_curve_function_with_length) removed code duplication with get_nth_curve_function_length_pieces

* fix(OpenGLVMobject) removed duplcate assignment of self.n_points_per_curve

* fix(OpenGLMobject): changed to total assignment in interpolate function

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update manim/mobject/opengl/opengl_vectorized_mobject.py

Co-authored-by: Benjamin Hackl <devel@benjamin-hackl.at>

* Update manim/mobject/opengl/opengl_vectorized_mobject.py

Co-authored-by: Benjamin Hackl <devel@benjamin-hackl.at>

* Update opengl_vectorized_mobject.py

* Update opengl_vectorized_mobject.py

* use remapping instead of copying points

* added documentation

* (opengl_mobject): reverted interpolate

* cleanup

* revamping remap, now considering not only adding a single curve per triplet

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Benjamin Hackl <devel@benjamin-hackl.at>

Author: 3 people

manim/mobject/opengl/opengl_mobject.py

@@ -2394,6 +2394,7 @@ def construct(self):
                 func = interpolate
 
             self.data[key][:] = func(mobject1.data[key], mobject2.data[key], alpha)
+
         for key in self.uniforms:
             if key != "fixed_orientation_center":
                 self.uniforms[key] = interpolate(

manim/mobject/opengl/opengl_vectorized_mobject.py

@@ -21,6 +21,7 @@
     interpolate,
     partial_quadratic_bezier_points,
     proportions_along_bezier_curve_for_point,
+    quadratic_bezier_remap,
 )
 from manim.utils.color import *
 from manim.utils.config_ops import _Data
@@ -120,7 +121,6 @@ def __init__(
         self.flat_stroke = flat_stroke
         self.render_primitive = render_primitive
         self.triangulation_locked = triangulation_locked
-        self.n_points_per_curve = n_points_per_curve
 
         self.needs_new_triangulation = True
         self.triangulation = np.zeros(0, dtype="i4")
@@ -783,10 +783,7 @@ def get_nth_curve_function_with_length(
             sample_points = 10
 
         curve = self.get_nth_curve_function(n)
-
-        points = np.array([curve(a) for a in np.linspace(0, 1, sample_points)])
-        diffs = points[1:] - points[:-1]
-        norms = np.apply_along_axis(np.linalg.norm, 1, diffs)
+        norms = self.get_nth_curve_length_pieces(n, sample_points)
 
         length = np.sum(norms)
 
@@ -1285,10 +1282,7 @@ def interpolate(self, mobject1, mobject2, alpha, *args, **kwargs):
         return self
 
     def pointwise_become_partial(
-        self,
-        vmobject: OpenGLVMobject,
-        a: float,
-        b: float,
+        self, vmobject: OpenGLVMobject, a: float, b: float, remap: bool = True
     ) -> OpenGLVMobject:
         """Given two bounds a and b, transforms the points of the self vmobject into the points of the vmobject
         passed as parameter with respect to the bounds. Points here stand for control points of the bezier curves (anchors and handles)
@@ -1301,58 +1295,58 @@ def pointwise_become_partial(
             upper-bound.
         b : float
             lower-bound
+        remap : bool
+            if the point amount should be kept the same (True)
+            This option should be manually set to False if keeping the number of points is not needed
         """
         assert isinstance(vmobject, OpenGLVMobject)
-        if a <= 0 and b >= 1:
-            self.become(vmobject)
-            return self
-        num_curves = vmobject.get_num_curves()
-        nppc = self.n_points_per_curve
-
         # Partial curve includes three portions:
         # - A middle section, which matches the curve exactly
-        # - A start, which is some ending portion of an inner quadratic
-        # - An end, which is the starting portion of a later inner quadratic
-
-        lower_index, lower_residue = integer_interpolate(0, num_curves, a)
-        upper_index, upper_residue = integer_interpolate(0, num_curves, b)
-        i1 = nppc * lower_index
-        i2 = nppc * (lower_index + 1)
-        i3 = nppc * upper_index
-        i4 = nppc * (upper_index + 1)
-
-        vm_points = vmobject.points
-        new_points = vm_points.copy()
-        if num_curves == 0:
-            new_points[:] = 0
+        # - A start, which is some ending portion of an inner cubic
+        # - An end, which is the starting portion of a later inner cubic
+        if a <= 0 and b >= 1:
+            self.set_points(vmobject.points)
+            return self
+        bezier_triplets = vmobject.get_bezier_tuples()
+        num_quadratics = len(bezier_triplets)
+
+        # The following two lines will compute which bezier curves of the given mobject need to be processed.
+        # The residue basically indicates the proportion of the selected Bèzier curve.
+        # Ex: if lower_index is 3, and lower_residue is 0.4, then the algorithm will append to the points 0.4 of the third bezier curve
+        lower_index, lower_residue = integer_interpolate(0, num_quadratics, a)
+        upper_index, upper_residue = integer_interpolate(0, num_quadratics, b)
+        self.clear_points()
+        if num_quadratics == 0:
             return self
         if lower_index == upper_index:
-            tup = partial_quadratic_bezier_points(
-                vm_points[i1:i2],
-                lower_residue,
-                upper_residue,
+            self.append_points(
+                partial_quadratic_bezier_points(
+                    bezier_triplets[lower_index],
+                    lower_residue,
+                    upper_residue,
+                ),
             )
-            new_points[:i1] = tup[0]
-            new_points[i1:i4] = tup
-            new_points[i4:] = tup[2]
-            new_points[nppc:] = new_points[nppc - 1]
         else:
-            low_tup = partial_quadratic_bezier_points(
-                vm_points[i1:i2],
-                lower_residue,
-                1,
+            self.append_points(
+                partial_quadratic_bezier_points(
+                    bezier_triplets[lower_index], lower_residue, 1
+                ),
             )
-            high_tup = partial_quadratic_bezier_points(
-                vm_points[i3:i4],
-                0,
-                upper_residue,
+            inner_points = bezier_triplets[lower_index + 1 : upper_index]
+            if len(inner_points) > 0:
+                if remap:
+                    new_triplets = quadratic_bezier_remap(
+                        inner_points, num_quadratics - 2
+                    )
+                else:
+                    new_triplets = bezier_triplets
+
+                self.append_points(np.asarray(new_triplets).reshape(-1, 3))
+            self.append_points(
+                partial_quadratic_bezier_points(
+                    bezier_triplets[upper_index], 0, upper_residue
+                ),
             )
-            new_points[0:i1] = low_tup[0]
-            new_points[i1:i2] = low_tup
-            # Keep new_points i2:i3 as they are
-            new_points[i3:i4] = high_tup
-            new_points[i4:] = high_tup[2]
-        self.set_points(new_points)
         return self
 
     def get_subcurve(self, a: float, b: float) -> OpenGLVMobject:

manim/utils/bezier.py

@@ -175,6 +175,62 @@ def subdivide_quadratic_bezier(points: Iterable[float], n: int) -> np.ndarray:
     return np.asarray(beziers).reshape(-1, 3)
 
 
+def quadratic_bezier_remap(
+    triplets: Iterable[Iterable[float]], new_number_of_curves: int
+):
+    """Remaps the number of curves to a higher amount by splitting bezier curves
+
+    Parameters
+    ----------
+    triplets
+        The triplets of the quadratic bezier curves to be remapped
+
+    new_number_of_curves
+        The number of curves that the output will contain. This needs to be higher than the current number.
+
+    Returns
+    -------
+        The new triplets for the quadratic bezier curves.
+    """
+    difference = new_number_of_curves - len(triplets)
+    if difference <= 0:
+        return triplets
+    new_triplets = np.zeros((new_number_of_curves, 3, 3))
+    idx = 0
+    for triplet in triplets:
+        if difference > 0:
+            tmp_noc = int(np.ceil(difference / len(triplets))) + 1
+            tmp = subdivide_quadratic_bezier(triplet, tmp_noc).reshape(-1, 3, 3)
+            for i in range(tmp_noc):
+                new_triplets[idx + i] = tmp[i]
+            difference -= tmp_noc - 1
+            idx += tmp_noc
+        else:
+            new_triplets[idx] = triplet
+            idx += 1
+    return new_triplets
+
+    """
+    This is an alternate version of the function just for documentation purposes
+    --------
+
+    difference = new_number_of_curves - len(triplets)
+    if difference <= 0:
+        return triplets
+    new_triplets = []
+    for triplet in triplets:
+        if difference > 0:
+            tmp_noc = int(np.ceil(difference / len(triplets))) + 1
+            tmp = subdivide_quadratic_bezier(triplet, tmp_noc).reshape(-1, 3, 3)
+            for i in range(tmp_noc):
+                new_triplets.append(tmp[i])
+            difference -= tmp_noc - 1
+        else:
+            new_triplets.append(triplet)
+    return new_triplets
+    """
+
+
 # Linear interpolation variants