#x (predefined symbol)
|int||Always, except in global sections||Never||No|
This predefined symbol returns the x-coordinate of the pixel currently being calculated. You can also use the predefined symbol #screenpixel to retrieve the x-coordinate, but there is an important difference.
The coordinates accessible through #screenpixel are float coordinates, while #x and #y contain int coordinates. For normal fractal calculations, this doesn’t matter. It does matter, however, when using the Render to Disk feature with anti-aliasing. In this case, Ultra Fractal can subdivide pixels and calculate pixels that actually fall between the physical pixels on the screen. The coordinates of these subdivided pixels cannot be properly expressed using int values, of course.
So if your formula uses the #x and #y predefined symbols, it won’t work properly with anti-aliasing. It will work properly with anti-aliasing if it uses the #screenpixel predefined symbol instead. You should decide how your formula should work and choose the right predefined symbol for the job. Of course, you can also experiment and see which choice works best with your formula.
int i = #x
Note: When anti-aliasing, #x ranges from 0 up to and including #width. If you use #x to index an array, you should declare the array with size [#width + 1].