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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.