对于VMobject的深入研究

首先，VMobject是由anchors和handles实现的贝塞尔曲线，例如：

        def playscene0():
            plane = NumberPlane()
            vmobject = VMobject(color=GREEN)
            vmobject.points = [
                np.array([-3, 0, 0]),
                np.array([-3, 2, 0]),
                np.array([-2, 3, 0]),
                np.array([0, 3, 0]),
                np.array([0, 3, 0]), 
                np.array([2, 3, 0]),
                np.array([3, 2, 0]),
                np.array([3, 0, 0]),
            ]
            sa(plane, vmobject);sw()

其次，我们来考察一下内置的VMobject：

        def playscene0():
            c = Text('C')[0]  # 注意要加索引，否则为空数组
            li = c.get_anchors_and_handles()
            print(li)

结果为：

[array([[ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17],
       [-6.63085750e-02, -2.25390650e-01,  2.76023938e-17],
       [-1.33496075e-01, -1.78320300e-01,  2.18379385e-17],
       [-1.79785175e-01, -1.03515650e-01,  1.26770109e-17],
       [-1.96972675e-01, -4.10155000e-03,  5.02295008e-19],
       [-1.80175775e-01,  9.64843500e-02, -1.18159250e-17],
       [-1.33300775e-01,  1.74023450e-01, -2.13117261e-17],
       [-6.33788750e-02,  2.24023450e-01, -2.74349601e-17],
       [ 2.29492250e-02,  2.41601550e-01, -2.95876565e-17],
       [ 8.46679750e-02,  2.33007800e-01, -2.85352256e-17],
       [ 1.37402325e-01,  2.09375000e-01, -2.56410424e-17],
       [ 1.50683625e-01,  2.31445300e-01, -2.83438746e-17],
       [ 1.76660175e-01,  2.31445300e-01, -2.83438746e-17],
       [ 1.79589825e-01,  6.67968500e-02, -8.18025485e-18],
       [ 1.53027325e-01,  6.67968500e-02, -8.18025485e-18],
       [ 1.37207025e-01,  1.18945300e-01, -1.45665981e-17],
       [ 1.12988275e-01,  1.66601550e-01, -2.04028055e-17],
       [ 7.58789250e-02,  2.01367200e-01, -2.46603697e-17],
       [ 2.68554750e-02,  2.13867200e-01, -2.61911782e-17],
       [-3.19335750e-02,  1.99804700e-01, -2.44690186e-17],
       [-7.88085750e-02,  1.58398450e-01, -1.93982155e-17],
       [-1.08496075e-01,  9.12109500e-02, -1.11701198e-17],
       [-1.19238275e-01,  3.90650000e-04, -4.78408272e-20],
       [-1.08105475e-01, -8.08593500e-02,  9.90241442e-18],
       [-7.58788750e-02, -1.45703150e-01,  1.78434896e-17],
       [-2.66601750e-02, -1.89062500e-01,  2.31534785e-17],
       [ 3.68164250e-02, -2.04687500e-01,  2.50669892e-17],
       [ 8.52539250e-02, -1.96484350e-01,  2.40623930e-17],
       [ 1.23730475e-01, -1.74414050e-01,  2.13595608e-17],
       [ 1.52246125e-01, -1.41992200e-01,  1.73890293e-17],
       [ 1.72558625e-01, -1.02148450e-01,  1.25095772e-17],
       [ 1.96972675e-01, -1.13867200e-01,  1.39447102e-17],
       [ 1.22753925e-01, -2.12109350e-01,  2.59759037e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17]]), array([[-1.47460750e-02, -2.41601550e-01,  2.95876565e-17],
       [-9.16992250e-02, -2.14648450e-01,  2.62868537e-17],
       [-1.53027325e-01, -1.58007800e-01,  1.93503747e-17],
       [-1.91503875e-01, -7.42187500e-02,  9.08917546e-18],
       [-1.97167975e-01,  3.28125000e-02, -4.01837231e-18],
       [-1.68847675e-01,  1.26562500e-01, -1.54994361e-17],
       [-1.13574225e-01,  1.95507800e-01, -2.39428001e-17],
       [-3.66210750e-02,  2.35546850e-01, -2.88461696e-17],
       [ 4.54101750e-02,  2.41406250e-01, -2.95637391e-17],
       [ 1.03027325e-01,  2.27343750e-01, -2.78415796e-17],
       [ 1.41829425e-01,  2.16731767e-01, -2.65419864e-17],
       [ 1.59342475e-01,  2.31445300e-01, -2.83438746e-17],
       [ 1.77636725e-01,  1.76562483e-01, -2.16226680e-17],
       [ 1.70735658e-01,  6.67968500e-02, -8.18025485e-18],
       [ 1.49316425e-01,  8.26172000e-02, -1.01176890e-17],
       [ 1.30175775e-01,  1.37500000e-01, -1.68388935e-17],
       [ 1.02441425e-01,  1.81250000e-01, -2.21967232e-17],
       [ 6.14257750e-02,  2.09570300e-01, -2.56649597e-17],
       [ 5.56642500e-03,  2.13671850e-01, -2.61672547e-17],
       [-5.00976750e-02,  1.90429700e-01, -2.33209123e-17],
       [-9.15038750e-02,  1.40625000e-01, -1.72215956e-17],
       [-1.15722675e-01,  6.40625000e-02, -7.84539356e-18],
       [-1.19238275e-01, -2.91015500e-02,  3.56391201e-18],
       [-1.00683575e-01, -1.05664050e-01,  1.29401141e-17],
       [-6.22070250e-02, -1.64453150e-01,  2.01397024e-17],
       [-7.71482500e-03, -1.99609350e-01,  2.44450952e-17],
       [ 5.41992250e-02, -2.04687500e-01,  2.50669892e-17],
       [ 1.00097675e-01, -1.91015650e-01,  2.33926704e-17],
       [ 1.34277325e-01, -1.65039050e-01,  2.02114544e-17],
       [ 1.60449225e-01, -1.29882800e-01,  1.59060555e-17],
       [ 1.80696642e-01, -1.06054700e-01,  1.29879549e-17],
       [ 1.78027325e-01, -1.59765650e-01,  1.95656492e-17],
       [ 9.18945250e-02, -2.31835940e-01,  2.83917142e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17]]), array([[-4.11132750e-02, -2.36328150e-01,  2.89418512e-17],
       [-1.14160175e-01, -1.98828150e-01,  2.43494257e-17],
       [-1.68457025e-01, -1.33203150e-01,  1.63126811e-17],
       [-1.97167975e-01, -4.10156500e-02,  5.02296845e-18],
       [-1.91503875e-01,  6.64062500e-02, -8.13242015e-18],
       [-1.53222675e-01,  1.52343750e-01, -1.86567286e-17],
       [-9.03320250e-02,  2.12109350e-01, -2.59759037e-17],
       [-7.91017500e-03,  2.41406250e-01, -2.95637391e-17],
       [ 6.61132750e-02,  2.38671850e-01, -2.92288717e-17],
       [ 1.20605475e-01,  2.19335950e-01, -2.68609069e-17],
       [ 1.46256525e-01,  2.24088533e-01, -2.74429305e-17],
       [ 1.68001325e-01,  2.31445300e-01, -2.83438746e-17],
       [ 1.78613275e-01,  1.21679667e-01, -1.49014614e-17],
       [ 1.61881492e-01,  6.67968500e-02, -8.18025485e-18],
       [ 1.44042975e-01,  1.00000000e-01, -1.22464680e-17],
       [ 1.22167975e-01,  1.53320300e-01, -1.87763215e-17],
       [ 9.01367250e-02,  1.92968750e-01, -2.36318562e-17],
       [ 4.50195250e-02,  2.13671850e-01, -2.61672547e-17],
       [-1.39648250e-02,  2.08984350e-01, -2.55932015e-17],
       [-6.57226750e-02,  1.76562500e-01, -2.16226700e-17],
       [-1.01464825e-01,  1.18359350e-01, -1.44948399e-17],
       [-1.19238275e-01,  3.37890500e-02, -4.13796519e-18],
       [-1.15527325e-01, -5.62500000e-02,  6.88863825e-18],
       [-8.99413750e-02, -1.27343750e-01,  1.55951116e-17],
       [-4.58007750e-02, -1.78906250e-01,  2.19096966e-17],
       [ 1.33789250e-02, -2.04687500e-01,  2.50669892e-17],
       [ 7.04101750e-02, -2.01953150e-01,  2.47321279e-17],
       [ 1.12792975e-01, -1.83789050e-01,  2.25076672e-17],
       [ 1.43847675e-01, -1.54101550e-01,  1.88719970e-17],
       [ 1.67285175e-01, -1.16601550e-01,  1.42795715e-17],
       [ 1.88834658e-01, -1.09960950e-01,  1.34663325e-17],
       [ 1.53417975e-01, -1.92578150e-01,  2.35840215e-17],
       [ 5.51757750e-02, -2.41601550e-01,  2.95876565e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17]]), array([[-6.63085750e-02, -2.25390650e-01,  2.76023938e-17],
       [-1.33496075e-01, -1.78320300e-01,  2.18379385e-17],
       [-1.79785175e-01, -1.03515650e-01,  1.26770109e-17],
       [-1.96972675e-01, -4.10155000e-03,  5.02295008e-19],
       [-1.80175775e-01,  9.64843500e-02, -1.18159250e-17],
       [-1.33300775e-01,  1.74023450e-01, -2.13117261e-17],
       [-6.33788750e-02,  2.24023450e-01, -2.74349601e-17],
       [ 2.29492250e-02,  2.41601550e-01, -2.95876565e-17],
       [ 8.46679750e-02,  2.33007800e-01, -2.85352256e-17],
       [ 1.37402325e-01,  2.09375000e-01, -2.56410424e-17],
       [ 1.50683625e-01,  2.31445300e-01, -2.83438746e-17],
       [ 1.76660175e-01,  2.31445300e-01, -2.83438746e-17],
       [ 1.79589825e-01,  6.67968500e-02, -8.18025485e-18],
       [ 1.53027325e-01,  6.67968500e-02, -8.18025485e-18],
       [ 1.37207025e-01,  1.18945300e-01, -1.45665981e-17],
       [ 1.12988275e-01,  1.66601550e-01, -2.04028055e-17],
       [ 7.58789250e-02,  2.01367200e-01, -2.46603697e-17],
       [ 2.68554750e-02,  2.13867200e-01, -2.61911782e-17],
       [-3.19335750e-02,  1.99804700e-01, -2.44690186e-17],
       [-7.88085750e-02,  1.58398450e-01, -1.93982155e-17],
       [-1.08496075e-01,  9.12109500e-02, -1.11701198e-17],
       [-1.19238275e-01,  3.90650000e-04, -4.78408272e-20],
       [-1.08105475e-01, -8.08593500e-02,  9.90241442e-18],
       [-7.58788750e-02, -1.45703150e-01,  1.78434896e-17],
       [-2.66601750e-02, -1.89062500e-01,  2.31534785e-17],
       [ 3.68164250e-02, -2.04687500e-01,  2.50669892e-17],
       [ 8.52539250e-02, -1.96484350e-01,  2.40623930e-17],
       [ 1.23730475e-01, -1.74414050e-01,  2.13595608e-17],
       [ 1.52246125e-01, -1.41992200e-01,  1.73890293e-17],
       [ 1.72558625e-01, -1.02148450e-01,  1.25095772e-17],
       [ 1.96972675e-01, -1.13867200e-01,  1.39447102e-17],
       [ 1.22753925e-01, -2.12109350e-01,  2.59759037e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17],
       [ 1.27929750e-02, -2.41601550e-01,  2.95876565e-17]])]

于是我尝试通过anchors和handles来实现自定义的VMobject，以正方形为例：

            c = Square()
            li = c.get_anchors_and_handles()  # 获取VMobject的anchors和handles
            l = len(li[0])  # 注意li的长度为4，这意味这[li[0][i],li[1][i],li[2][i],li[3][i]]组成一条贝塞尔曲线
            v = VMobject()  # 创建空的VMobject
            myli = []
            for i in range(l):
                myli.append(li[0][i]);myli.append(li[1][i]);myli.append(li[2][i]);myli.append(li[3][i])  # 注意不需要加[]
            v.points = myli
            sa(v);sw()

如果将c改为Text也可以实现（注意要加索引）

注意这样产生的VMobject仅仅是一个轮廓，即DrawBorderThenFill().get_outline()，我们可以通过更改VMobject的属性：

v = VMobject(stroke_width=10, fill_color=BLUE, fill_opacity=1)

注意观察stroke_width的含义，例如，对正方形来说，我们并没有绘制内外两条贝塞尔曲线，只是绘制了一条曲线（四条边，而不是八条边）：

[array([1., 1., 0.]), array([0.33333333, 1., 0.]), array([-0.33333333, 1., 0.]), array([-1., 1., 0.]),
 array([-1., 1., 0.]), array([-1., 0.33333333, 0.]), array([-1., -0.33333333, 0.]), array([-1., -1., 0.]),
 array([-1., -1., 0.]), array([-0.33333333, -1., 0.]), array([ 0.33333333, -1., 0.]), array([ 1., -1., 0.]),
 array([ 1., -1., 0.]), array([ 1., -0.33333333, 0.]), array([1., 0.33333333, 0.]), array([1., 1., 0.])]