Fix drawing terminator, round usec

for some reason rounding is giving me wrong results
not sure what i'm doing wrong :D

just show 6 digits :P

ok this gets the us/iter working, and it is more stable
but the elapsed time still needs to be added

.mailmap

@@ -0,0 +1,2 @@
+Brooke Vibber <bvibber@pobox.com>
+Brooke Vibber <bvibber@pobox.com> <brion@pobox.com>

Makefile

@@ -2,8 +2,8 @@
 
 all : mandel.xex
 
-mandel.xex : mandel.o tables.o
+mandel.xex : mandel.o tables.o atari-asm-xex.cfg
-	ld65 -C ./atari-asm-xex.cfg -o $@ $+
+	ld65 -C ./atari-asm-xex.cfg -o $@ mandel.o tables.o
 
 %.o : %.s
 	ca65 -o $@ $<

atari-asm-xex.cfg

@@ -0,0 +1,28 @@
+FEATURES {
+    STARTADDRESS: default = $2E00;
+}
+SYMBOLS {
+    __STARTADDRESS__: type = export, value = %S;
+}
+MEMORY {
+    ZP:      file = "", define = yes, start = $0082, size = $007E;
+    MAIN:    file = %O, define = yes, start = %S,    size = $4000 - %S;
+    # Keep $4000-7fff clear for expanded RAM access window
+    TABLES:  file = %O, define = yes, start = $8000, size = $a000 - $8000;
+    # Keep $a000-$bfff clear for BASIC cartridge
+}
+FILES {
+    %O: format = atari;
+}
+FORMATS {
+    atari: runad = start;
+}
+SEGMENTS {
+    ZEROPAGE: load = ZP,      type = zp,  optional = yes;
+    EXTZP:    load = ZP,      type = zp,  optional = yes; # to enable modules to be able to link to C and assembler programs
+    CODE:     load = MAIN,    type = rw,                  define = yes;
+    RODATA:   load = MAIN,    type = ro   optional = yes;
+    DATA:     load = MAIN,    type = rw   optional = yes;
+    BSS:      load = MAIN,    type = bss, optional = yes, define = yes;
+    TABLES:   load = TABLES,  type = ro,  optional = yes, align = 256;
+}

readme.md

@@ -14,30 +14,37 @@ Non-goals:
 
 Enjoy! I'll probably work on this off and on for the next few weeks until I've got it producing fractals.
 
--- brion, january 2023
+-- brooke, january 2023 - december 2024
 
 ## 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 6 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 3.13-precision fixed point numbers with 6.26-precision intermediates.
 
 Iterations are capped at 255.
 
-## Next steps
+The pixels are run in a progressive layout to get the basic shape on screen faster.
 
-Add a running counter of ms/px using the vertical blank interrupts as a timer. This'll show how further work improves it!
+There is a running counter of ms/px using the vertical blank interrupts as a timer, used to track our progress. :D
 
-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 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.
 
-I may be able to do a faster multiply using tables of squares for 8-bit component multiplication.
+There's some cute color cycling.
 
 ## 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.
 
 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`.

tables.js

@@ -11,23 +11,40 @@ function db(func) {
     return lines.join('\n');
 }
 
+let squares = [];
+for (let i = 0; i < 512; i++) {
+    squares.push(Math.trunc((i * i + 1) / 2));
+}
+
 console.log(
 `.segment "TABLES"
 
 .export mul_lobyte256
 .export mul_hibyte256
 .export mul_hibyte512
+.export sqr_lobyte
+.export sqr_hibyte
 
+; (i * i + 1) / 2 for the multiplier
 .align 256
 mul_lobyte256:
-${db((x) => Math.round(x * x / 2) & 0xff)}
+${db((i) => squares[i] & 0xff)}
 
 .align 256
 mul_hibyte256:
-${db((x) => (Math.round(x * x / 2) >> 8) & 0xff)}
+${db((i) => (squares[i] >> 8) & 0xff)}
 
 .align 256
 mul_hibyte512:
-${db((x) => (Math.round((x + 256) * (x + 256) / 2) >> 8) & 0xff)}
+${db((i) => (squares[i + 256] >> 8) & 0xff)}
+
+; (i * i) for the plain squares
+.align 256
+sqr_lobyte:
+${db((i) => (i * i) & 0xff)}
+
+.align 256
+sqr_hibyte:
+${db((i) => ((i * i) >> 8) & 0xff)}
 
 `);

todo.md

@@ -0,0 +1,17 @@
+things to try:
+
+* fix status bar to show elapsed time, per-iter time, per-pixel iter count
+
+* 'turbo' mode disabling graphics in full or part
+
+* patch the entire expanded-ram imul8xe on top of imul8 to avoid the 3-cycle thunk penalty :D
+
+* maybe clean up the load/layout of the big mul table
+
+* consider alternate lookup tables in the top 16KB under ROM
+
+* y-axis mirror optimization
+
+* extract viewport for display & re-input via keyboard
+
+* fujinet screenshot/viewport uploader