Plug-in parameters

Like formulas, classes can also have parameters and a title, which are declared in the default section. This matters only if the class is used by a plug-in parameter for a formula. Classes used by plug-in parameters are called plug-ins.

When used as a plug-in, the class appears in the list of parameters in the Layer Properties tool window, with the parameters for the class grouped with the title of the class. (See Example 1 - Formula plug-ins for a screen shot.)

Here is a simple example of a class that implements a simple bailout condition for a Mandelbrot-like fractal formula. The bailout value is exposed as a parameter.

class Bailout {
public:
  func Bailout()
    ; Empty constructor, see Writing plug-ins
  endfunc
  bool func hasBailedOut(const complex z)
    return |z| > @bailout
  endfunc
default:
  title = "Simple Bailout"
  float param bailout
    caption = "Bailout value"
    default = 4
    min = 1
  endparam
}

To be able to use this class as a plug-in and include its parameters in the parameter list for a formula, declare a plug-in parameter in the formula. A plug-in parameter is declared by a parameter block with a class as the parameter type.

MandelbrotTest {
init:
  z = (0, 0)
  Bailout bo = new @bailoutParam
loop:
  z = sqr(z) + #pixel
bailout:
  !bo.hasBailedOut(z)
default:
  Bailout param bailoutParam
    caption = "Bailout Test"
  endparam
}

Notes

Normally, you create an instance of a class with parameters using new and the class name. In this case, all parameters always remain at the default value. The plug-in parameter bailoutParam in the MandelbrotTest formula represents a variant of the Bailout class that has different parameter values, set by the user. To create an object that uses these user-set parameter values, use the new operator with the plug-in parameter as shown above.
You can create more than one object from a single plug-in parameter, and you can have multiple plug-in parameters of the same class type, which each have their own independent set of parameters.
Inside the class declaration for a plug-in, all parameters must be declared by a parameter block. (In contrast, formulas can have undeclared parameters for Fractint compatibility.)
Optionally, a class used as a plug-in can also contain a rating setting in its default section.

Next: Writing plug-ins