!!omap
- name: pendulum
- parts:
  - name: head
    shapes:
      libraries: ['from math import tan, radians, sin, cos', 'from pysketcher import *']
  - name: constants
    shapes:
        H: 7.0
        W: 6.0
  - name: frame
    shapes:
        setframe:          # sketch setup
            action: drawing_tool.set_coordinate_system(xmin=0, xmax=W,
                                   ymin=0, ymax=H,
                                   axis=False)
        setblackline:      # default frame values and actions
            action: drawing_tool.set_linecolor('blue')
        L: 5*H/7          # length
        P: (W/6, 0.85*H)  # rotation point
        a: 40             # angle
        vertical: 
            formula: Line(P, P-point(0,L))
            style:
                linecolor: black
                linewidth: 1
        path: 
            formula: Arc(P, L, -90, a)
            style:
                linecolor: black
                linewidth: 1
        angle: Arc_wText(r'$\theta$', P, L/4, -90, a, text_spacing=1/30.)

        #rod: Line(P, P + L*point(sin(radians(a)), -L*cos(radians(a)))) is a less reliable alternative
        mass_pt: path.geometric_features()['end']
        rod: Line(P, mass_pt)

        mass: 
            formula: Circle(center=mass_pt, radius=L/20.)
            style:
                filled_curves: 
                    color: 'blue'
        rod_vec: rod.geometric_features()['end'] - rod.geometric_features()['start']
        unit_rod_vec: unit_vec(rod_vec)
        mass_symbol: Text('$m$', mass_pt + L/10*unit_rod_vec)

        length: 
            formula: Distance_wText(P, mass_pt, '$L$') # Displace length indication
            transform: translate(L/15*point(cos(radians(a)), sin(radians(a))))
        gravity: Gravity(start=P+point(0.8*L,0), length=L/3)

        pendulum: "Composition({'body': mass, 'rod': rod,'vertical': vertical, 'theta': angle, 'path': path,'g': gravity, 'L': length, 'm': mass_symbol})"