From 64a6cf50f3a5d7aa46632b6ab8f83120e2c49448 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Mon, 30 Dec 2024 10:21:52 -0800
Subject: [PATCH] awesome new palette cycler

---
 mandel.s | 108 ++++++++++++++++++++++++++++++++++++++++++-------------
 todo.md  |   2 --
 2 files changed, 84 insertions(+), 26 deletions(-)

diff --git a/mandel.s b/mandel.s
index 90396d4..198e40c 100644
--- a/mandel.s
+++ b/mandel.s
@@ -13,13 +13,13 @@ zy_2  = $92     ; fixed4.12: z_y^2
 zx_zy = $94     ; fixed4.12: z_x * z_y
 dist  = $96     ; fixed4.12: z_x^2 + z_y^2
 
-iter         = $a0 ; u8: iteration count
+iter          = $a0 ; u8: iteration count
 
-zoom         = $a1 ; u8: zoom shift level
-count_frames = $a2 ; u8
-count_pixels = $a3 ; u8
-total_ms     = $a4 ; float48
-total_pixels = $aa ; float48
+zoom          = $a1 ; u8: zoom shift level
+count_frames  = $a2 ; u8
+count_pixels  = $a3 ; u8
+total_ms      = $a4 ; float48
+total_pixels  = $aa ; float48
 
 z_buffer_active = $b0 ; boolean: 1 if we triggered the lake, 0 if not
 z_buffer_start  = $b1 ; u8: index into z_buffer
@@ -34,6 +34,14 @@ pixel_offset    = $bd ; u8
 fill_level      = $be ; u8
 palette_offset  = $bf ; u8
 
+palette_ticks = $c0 ; u8
+chroma_ticks  = $c1 ; u8
+chroma_offset = $c2 ; u8
+
+palette_delay = 120
+chroma_delay = 120
+
+
 ; FP registers in zero page
 FR0    = $d4 ; float48
 FRE    = $da
@@ -224,11 +232,26 @@ color_map:
         .byte 3
     .endrepeat
 
-palette:
-    .byte $00
-    .byte $46
-    .byte $78
-    .byte $b4
+
+palette_start:
+    .byte $04
+    .byte $08
+    .byte $0e
+palette_repeat:
+    .byte $03
+    .byte $09
+
+palette_entries = 3
+
+palette_chroma:
+    .repeat 15, i
+        .byte (i + 1) << 4
+    .endrepeat
+    .repeat 2, i
+        .byte (i + 1) << 4
+    .endrepeat
+palette_chroma_entries = 15
+
 .code
 
 z_buffer_len = 16
@@ -1136,31 +1159,65 @@ done:
 
 .proc vblank_handler
     inc count_frames
+
+    inc chroma_ticks
+    lda chroma_ticks
+    cmp #(chroma_delay)
+    bne skip_chroma
+
+    lda #0
+    sta chroma_ticks
+
+    inc chroma_offset
+    lda chroma_offset
+    cmp #(palette_chroma_entries)
+    bne skip_chroma
+
+    lda #0
+    sta chroma_offset
+skip_chroma:
+
+    inc palette_ticks
+    lda palette_ticks
+    cmp #(palette_delay)
+    bne skip_luma
+
+    lda #0
+    sta palette_ticks
+
     inc palette_offset
+    lda palette_offset
+    cmp #(palette_entries)
+    bne skip_luma
+
+    lda #0
+    sta palette_offset
+
+skip_luma:
     jsr update_palette
     jmp XITVBV
 .endproc
 
 .proc update_palette
-    lda palette
+    lda #0
     sta COLOR4
 
-    clc
-    lda palette_offset
-    and #$f0
-    adc palette + 1
+    ldx chroma_offset
+    ldy palette_offset
+    lda palette_chroma,x
+    ora palette_start,y
     sta COLOR0
 
-    clc
-    lda palette_offset
-    and #$f0
-    adc palette + 2
+    inx
+    iny
+    lda palette_chroma,x
+    ora palette_start,y
     sta COLOR1
 
-    clc
-    lda palette_offset
-    and #$f0
-    adc palette + 3
+    inx
+    iny
+    lda palette_chroma,x
+    ora palette_start,y
     sta COLOR2
 
     rts
@@ -1358,6 +1415,9 @@ copy_byte_loop:
     ; Initialize the palette
     lda #0
     sta palette_offset
+    sta palette_delay
+    sta chroma_offset
+    sta chroma_delay
     jsr update_palette
 
     ; install the vblank handler
diff --git a/todo.md b/todo.md
index 6c6d84d..a8675af 100644
--- a/todo.md
+++ b/todo.md
@@ -11,8 +11,6 @@ things to try:
 
 * 'wide pixels' 2x and 4x for a fuller initial image in the tiered rendering
 
-* rework the palette cycling to look more like an advancing flow
-
 * extact viewport for display & re-input via keyboard
 
 * fujinet screenshot/viewport uploader