Mobject Controls

pop and swap

class QuadScene(Scene):
    def construct(self):

        a = MathTex("a", color=RED)
        b = MathTex("b", color=BLUE)
        c = MathTex("c", color=GREEN)

        tex = MathTex([[ a, "x^2" ], "+", [ b, "x" ], "+", [ c ]], "=", 0)
        self.add(tex).wait(1)

        a.pop()

        b.swap(lambda: Fraction(b, a))
        c.swap(lambda: Fraction(c, a))

        self.play(TransformInStages.progress(tex))

In this example:

• a.pop() disconnects \(a\) from \(ax^2\) and returns \(a\).

• b.swap(lambda: Fraction(b, a)) replaces \(b\) with \(\frac{b}{a}\) and returns \(\frac{b}{a}\).

• c.swap(lambda: Fraction(c, a)) replaces \(c\) with \(\frac{c}{a}\) and returns \(\frac{c}{a}\).

merge

term1.merge(term2), directs the animation generator to use a clone of term1 as the target mobject for term2.

class QuadraticMerge(Scene):
    def construct(self):

        a = MathTex("a", color=RED)
        b = MathTex("b", color=BLUE)

        paren1 = Paren([ "x", "+", Fraction(b, [ 2, a ])])
        paren2 = Paren([ "x", "+", Fraction(b, [ 2, a ])])

        tex = MathTex(paren1, paren2)
        self.add(tex)

        tex.terms = [ Term(paren1, 2) ] # paren2 is removed, but merges onto paren1 for remover-animation
        paren1.merge(paren2)

        self.play(TransformInStages.progress(tex, lag_ratio=0.5))

class FractionMerge(Scene):
    def construct(self):

        a = MathTex("a", color=RED)
        b = MathTex("b", color=BLUE)
        c = MathTex("c", color=GREEN)

        frac1 = Fraction(
            Term(b, 2),
            [ 4, Term(a, 2) ]
        )

        frac2 = Fraction(
            [ 4, a, c ],
            [ 4, Term(a, 2) ]
        )

        tex = MathTex(frac1, "+", frac2)
        self.add(tex)


        frac1.numerator = MathTex(frac1.numerator, tex[1], frac2.numerator)
        frac1.denominator.merge(frac2.denominator)
        tex.terms = [ frac1 ]

        self.play(TransformInStages.progress(tex, lag_ratio=0.5))