formula property
A formula that takes angle and returns a amplitude factor (usually between -1.0 and 1.0).
If values less than -1.0 or greater than 1.0 are returned, then shape may go beyond the
rendering region. To ensure that it fits in the rendering region, set boxFit to BoxFit.fill
to resize resulting shape within the rendering region.
Implementation
final GuiPolarFunction formula;