brooke/mandel-6502
1
0
Fork 1
Code Issues Pull requests Projects Releases Packages Wiki Activity

update readme

Browse source
This commit is contained in:
Brooke Vibber 2024-12-30 16:50:25 -08:00
parent e6cbe0bc6b
commit ed79c80b16
1 changed files with 14 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

24
readme.md
View file

@ -14,15 +14,18 @@ Non-goals:
Enjoy! I'll probably work on this off and on for the next few weeks until I've got it producing fractals. Enjoy! I'll probably work on this off and on for the next few weeks until I've got it producing fractals.
-- brooke, january 2023 - february 2024 -- brooke, january 2023 - december 2024
## Current state ## Current state
Basic rendering is functional, but no interactive behavior (zoom/pan) or benchmarking is done yet. Basic rendering is functional, with interactive zoom/pan (+/-/arrows) and 4 preset viewports via the number keys.
The 16-bit signed integer multiplication works; it takes two 16-bit inputs and emits one 32-bit output in the zero page, using the Atari OS ROM's floating point registers as workspaces. Inputs are clobbered. The 16-bit signed integer multiplication takes two 16-bit inputs and emits one 32-bit output in the zero page, using the Atari OS ROM's floating point registers as workspaces. Inputs are clobbered.
The main loop is a basic add-and-shift, using 16-bit adds which requires flipping the sign of negative inputs (otherwise you'd have to add all those sign-extension bits). Runs in 470-780 cycles depending on input. * 16-bit multiplies are decomposed into 4 8-bit unsigned multiplies and some addition
* an optimized case for squares uses a table of 8-bit squares to reduce the number of 8-bit multiplication sub-ops
* when expanded RAM is available as on 130XE, a 64KB 8-bit multiplication table accelerates the remaining multiplications
* without expanded RAM, a table of half-squares is used to implement the algorithm from https://everything2.com/title/Fast+6502+multiplication
The mandelbrot calculations are done using 4.12-precision fixed point numbers. It may be possible to squish this down to 3.13. The mandelbrot calculations are done using 4.12-precision fixed point numbers. It may be possible to squish this down to 3.13.
@ -30,17 +33,18 @@ Iterations are capped at 255.
The pixels are run in a progressive layout to get the basic shape on screen faster. The pixels are run in a progressive layout to get the basic shape on screen faster.
## Next steps There is a running counter of ms/px using the vertical blank interrupts as a timer, used to track our progress. :D
Add a running counter of ms/px using the vertical blank interrupts as a timer. This'll show how further work improves it! There's a check for cycles in (zx,zy) output when in the 'lake'; if values repeat, they cannot escape. This is a big time saver in fractint.
Check for cycles in (zx,zy) output when in the 'lake'; if values repeat, they cannot escape. This is a big time saver in fractint. There's some cute color cycling.
I may be able to do a faster multiply using tables of squares for 8-bit component multiplication.
(done)
## Deps and build instructions ## Deps and build instructions
I'm using `ca65` as a macro assembler, and have a Unix-style `Makefile` for building. Should work fairly easily on Linux and Mac. Might work on "raw" Windows but I use WSL for that. I'm using `ca65` as a macro assembler, and have a Unix-style `Makefile` for building. Should work fairly easily on Linux and Mac. Might work on "raw" Windows but I use WSL for that.
Currently produces a `.xex` executable, which can be booted up in common Atari emulators and some i/o devices. Currently produces a `.xex` executable, which can be booted up in common Atari emulators and some i/o devices.
## Todo
See ideas in `todo.md`.