Compatibility

Ultra Fractal 4 accepts almost all formulas written for Ultra Fractal 3 and 2. There are some minor 

differences since Ultra Fractal 2:

G     

There are a three new 

keywords

: color, heading, and endheading. Variables with these 

names will have to be renamed. Parameters with these names should not be renamed to 

avoid breaking backwards compatibility. Instead, add a @ character to the parameter name 

in the parameter block that describes it, so the compiler will recognize it as a parameter, not 

as a keyword. For example, "param color" should be changed to "param @color".

G     

Some formulas might not run well with double precision (Ultra Fractal 2 always uses 

extended precision). In this case, either correct the formula, or adjust the Additional 

Precision value in the Formula tab of the 

Layer Properties

 tool window so extended 

precision is used. You can verify this in the 

Statistics

 tool window. Also see 

Arbitrary 

precision

.

G     

Functions that can return complex values with float arguments are treated differently. If the 

return value is assigned to a complex variable, the float argument is converted to complex 

and the complex version of the function is called instead of the float version. This fixes a 

number of bugs like:

complex

 c = sqrt(

 1

) 

; should be (0, 1)

Unfortunately, sometimes it breaks backwards compatibility because Ultra Fractal 2 would 

assign an invalid value to c in this case. To work around this, use:

float

 f = sqrt(

 1

)

complex

 c = f

The formula compiler is largely compatible with Fractint s parser and most Fractint formulas can be 

used without modification. There are a few exceptions, however:

G     

Writing to parameters is not recommended, since Ultra Fractal can perform special 

optimizations when parameters are read only. Formulas writing to parameters will be 

accepted, though.

G     

Writing to 

predefined symbols

 that are read only, such as 

#pixel

, is not allowed. Formulas 

writing to these predefined symbols will not be accepted.

G     

Formulas using the predefined symbol LastSqr will not be accepted. The usage of LastSqr 

serves no purpose; it is intended as a speed up but it only makes formulas run slower (even 

in Fractint). Furthermore it makes formulas very hard to write and to understand.

G     

Formulas using the function cosxx will not be accepted either. This function results from an 

early version of Fractint which contained a bug in the cos function. The cosxx function allows 

you to reproduce this bug in later versions of Fractint. If you still want to use the cosxx 

function, you can write 

conj

(

cos

(a)) instead of cosxx(a).

G     

In Fractint, functions with invalid arguments often return other values than in Ultra Fractal. 

For example. log(0) returns 0 in Fractint, but it returns  infinity in Ultra Fractal. This can 

cause problems. In general, if a Fractint formula gives a blank screen instead of a fractal, 

you should check the formula for this kind of errors (log(0), division by zero, recip(0), etc).

G     

Fractint iterates fractal formulas not the number of times given by the maximum iterations 

value, but one time less. Ultra Fractal does iterate fractal formulas the number of times 

given by the maximum iterations value. The Fractint PAR import feature in Ultra Fractal 

takes this into account and subtracts one from the maximum iterations value used by 

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