What is it ? :

This formula divide the complex plane into squares of length 1/2^n at the nth iteration. The point bails out if it is inside (or outside) a shape centered in this square. It can gives some Sierpinski-like patterns.
 

The Parameters :

Shape : Define the shape of the trap

Shape parameter : 
A parameter of the equation of the trap. The default value is set so that it works well with the Astroïd. So you might have to change it if you are using another shape. If you use the Pinch, change this value to 5 or 6 (or the number of "petals" you want the pinch to have). On some shape like the Circle or the Square, this parameter has no effect.

Threshold : 
Define how far from the curve a point is considered as inside. No effect on some shapes. If the points aren't bailed out fast enough (ie the image is messy and long to calculate) or are bailed out too fast, changing this value can help. In this case, you can also try changing the size of the shape.

Rotation Step : Allow you to rotate the trap at each iteration.

Invert z : Apply z -> 1/z before trapping. This can change the shape of the trap.

Graph functions : Only with the Graph shape. The graph shape is defined by f(x) = g(y). Set the y function to ident to get a "standard" graph.
 

Examples :

trap2
sq1
 

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