From c152c4346bf1bba5af4ee471d2e5bce71923cd34 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 4 Feb 2024 14:25:15 -0800
Subject: [PATCH] Progressive pixel layout

---
 mandel.s  | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++----
 readme.md |  4 +++-
 2 files changed, 62 insertions(+), 5 deletions(-)

diff --git a/mandel.s b/mandel.s
index ee99f05..ae8b897 100644
--- a/mandel.s
+++ b/mandel.s
@@ -31,7 +31,7 @@ pixel_color     = $b8 ; u8
 pixel_mask      = $b9 ; u8
 pixel_shift     = $ba ; u8
 pixel_offset    = $bb ; u8
-
+fill_level      = $bc ; u8
 
 ; FP registers in zero page
 FR0    = $d4 ; float48
@@ -218,6 +218,15 @@ z_buffer:
 
 .export start
 
+max_fill_level = 6
+fill_masks:
+    .byte %00011111
+    .byte %00001111
+    .byte %00000111
+    .byte %00000011
+    .byte %00000001
+    .byte %00000000
+
 ; 2 + 9 * byte cycles
 .macro add bytes, dest, arg1, arg2
     clc ; 2 cyc
@@ -959,6 +968,11 @@ copy_byte_loop:
     jsr SETVBV
 
 main_loop:
+    lda #0
+    sta fill_level
+
+fill_loop:
+
     ; sy = -92 .. 91
     lda #(256-half_height)
     sta sy
@@ -973,6 +987,40 @@ loop_sy:
     sta sx + 1
 
 loop_sx:
+    ; check the fill mask
+    ldy #0
+
+loop_skip_level:
+    cpy fill_level
+    beq current_level
+
+    lda fill_masks,y
+    and sx
+    bne not_skipped_mask1
+
+    lda fill_masks,y
+    and sy
+    beq skipped_mask
+
+not_skipped_mask1:
+    iny
+    jmp loop_skip_level
+
+current_level:
+    lda fill_masks,y
+    and sx
+    bne skipped_mask
+
+    lda fill_masks,y
+    and sy
+    beq not_skipped_mask
+
+skipped_mask:
+    jmp skipped
+
+not_skipped_mask:
+
+    ; run the fractal!
     zoom_factor cx, sx, zoom, aspect_x
     add16 cx, cx, ox
     zoom_factor cy, sy, zoom, aspect_y
@@ -983,7 +1031,7 @@ loop_sx:
     jsr keycheck
     beq no_key
     ; @fixme clear the pixel stats
-    jmp main_loop
+    jmp fill_loop
 
 no_key:
     ; check if we should update the counters
@@ -997,7 +1045,7 @@ no_key:
     ; count_frames >= 120? update!
     lda count_frames
     cmp #120 ; >= 2 seconds
-    bmi skip_status
+    bmi skipped
 
 update_status:
     ; FR0 = (float)count_pixels & clear count_pixels
@@ -1061,7 +1109,7 @@ update_status:
     draw_text_indirect speed_start, speed_precision, INBUFF
     draw_text speed_start + speed_precision, str_speed_len, str_speed
 
-skip_status:
+skipped:
 
     clc
     lda sx
@@ -1095,6 +1143,13 @@ loop_sy_done:
 
     draw_text 40 - str_done_len, str_done_len, str_done
 
+fill_loop_done:
+    inc fill_level
+    lda fill_level
+    cmp #max_fill_level
+    beq loop
+    jmp fill_loop
+
 loop:
     ; finished
     jsr keycheck
diff --git a/readme.md b/readme.md
index 46ebd36..6b57378 100644
--- a/readme.md
+++ b/readme.md
@@ -14,7 +14,7 @@ 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 - february 2024
 
 ## Current state
 
@@ -28,6 +28,8 @@ The mandelbrot calculations are done using 4.12-precision fixed point numbers. I
 
 Iterations are capped at 255.
 
+The pixels are run in a progressive layout to get the basic shape on screen faster.
+
 ## Next steps
 
 Add a running counter of ms/px using the vertical blank interrupts as a timer. This'll show how further work improves it!