Another 2 months later and kf-2.15.4 is ready. Kalles Fraktaler 2 + is fast deep zooming Free Software for fractal graphics (Mandelbrot, Burning Ship, etc). Full change log:

kf-2.15.4 (2021-07-22)

- new: rewritten GUI for window size / image size (by popular request)
- new: “imaginary axis points up” option in the transformation dialog (requested by saka and others, makes complex plane comply with maths conventions)
- new: Hidden Mandelbrot formula (thanks to FractalAlex, Bruce Dawson) https://fractalforums.org/f/22/t/3576/msg22122#msg22122
- new: Hidden Mandelbrot a la Cos formula (thanks to 3Dickulus) https://fractalforums.org/f/74/t/3591/msg22215#msg22215

- set Factor A real and imaginary parts to control shape (e.g. 1+1i)
- new: Polarbrot formula, for p = 2, 3, 4 (thanks to gerrit) https://fractalforums.org/f/15/t/1916/msg23377#msg23377

- set Factor A real part to control power a
- fractional and/or negative power a is possible
- known issue: need to set Bailout escape radius very high (but not so high that derivatives overflow: try 1e10 or so)
- known issue: for positive a, reference at 0 fails (blank image) (workaround: offset the center very slightly in the Location dialog)
- known issue: for negative a, blank image (workaround: set Formula seeds non-zero (1e-300); this will reduce accuracy for deeper zooms)
- known issue: seams with numeric differences DE (analytic DE is ok)
- known issue: Newton zooming is not functional yet
- known issue: auto-skew is not functional yet
- new: convert between built-in formulas and hybrid formulas (when possible) with new buttons in the Formula dialog
- new: option Ignore Hybrids in the Formula dialog to list only the built-in formulas that don’t have hybrid equivalents
- new: optimized some built-in formulas using common subexpression elimination (6%-58% faster perturbation calculations)

- Burning Ship power 2, 3, 4, 5
- Buffalo power 2, 3, 4
- new: optimized some hybrid OpenCL perturbation calculations
- fix: Hybrid operator multiplication works with OpenCL
- fix: Omnibrot works with OpenCL
- fix: Mandelbrot power 4 and above with derivatives works with OpenCL
- fix: formulas 52, 53, 69, 70, 71 now work with OpenCL
- fix: formulas 4 (power 3), 20, 23-26, 42-50 now have correct derivatives for analytic DE
- fix: renamed some formulas (Abs General Quadratic Plus/Minus, Omnibrot) (suggested by gerrit)
- fix: Zoom Amount spinner in Transformation dialog works live
- fix: Transformation dialog Zoom Amount sign inversion
- fix: right mouse button drag in Transformation dialog stretches in a more intuitive way
- fix: Transformation dialog displays/edits total transformation instead of difference from last set transformation
- fix: Newton zoom dialog (atom domain) size of period <=1 is set to 1
- fix: OpenCL error dialog no longer appears and disappears again instantly
- internal: formula build system refactored for parallel building and much faster incremental builds
- internal: include structure rationalized for faster builds
- internal: use intermediate ar archives for linking many object files
- internal: formula preprocessor supports temporary variables (can be used for common subexpression elimination)
- upgrade to gsl-2.7
- upgrade to openexr-2.5.7

Get it from mathr.co.uk/kf/kf.html.