From 6f05a9bbd057d0a3d7bfc963e2817117ad5463f5 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 18 Aug 2024 21:06:30 -0700
Subject: [PATCH] basic palette cycling

---
 mandel.s | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/mandel.s b/mandel.s
index 8cbd770..5976b73 100644
--- a/mandel.s
+++ b/mandel.s
@@ -32,6 +32,7 @@ pixel_mask      = $b9 ; u8
 pixel_shift     = $ba ; u8
 pixel_offset    = $bb ; u8
 fill_level      = $bc ; u8
+palette_offset  = $bd ; u8
 
 ; FP registers in zero page
 FR0    = $d4 ; float48
@@ -87,6 +88,12 @@ SYSVBV = $E45F
 XITVBV = $E462
 SETVBV = $E45C
 
+COLOR0 = $2C4
+COLOR1 = $2C5
+COLOR2 = $2C6
+COLOR3 = $2C7
+COLOR4 = $2C8
+
 ; Keycodes!
 KEY_PLUS  = $06
 KEY_MINUS = $0e
@@ -205,6 +212,11 @@ color_map:
         .byte 3
     .endrepeat
 
+palette:
+    .byte $00
+    .byte $36
+    .byte $88
+    .byte $d4
 .code
 
 z_buffer_len = 16
@@ -809,9 +821,33 @@ done:
 
 .proc vblank_handler
     inc count_frames
+    inc palette_offset
     jmp XITVBV
 .endproc
 
+.proc update_palette
+    lda palette
+    sta COLOR4
+
+    clc
+    lda palette_offset
+    and #$f0
+    adc palette + 1
+    sta COLOR0
+
+    clc
+    lda palette_offset
+    and #$f0
+    adc palette + 2
+    sta COLOR1
+
+    clc
+    lda palette_offset
+    and #$f0
+    adc palette + 3
+    sta COLOR2
+.endproc
+
 .proc update_speed
     ; convert frames (u16) to fp
     ; add to frames_total
@@ -971,6 +1007,11 @@ copy_byte_loop:
     lda #$22
     sta DMACTL
 
+    ; Initialize the palette
+    lda #0
+    sta palette_offset
+    jsr update_palette
+
     ; install the vblank handler
     lda #7 ; deferred
     ldx #.hibyte(vblank_handler)
@@ -1122,6 +1163,8 @@ update_status:
     draw_text_indirect speed_start, speed_precision, INBUFF
     draw_text speed_start + speed_precision, str_speed_len, str_speed
 
+    jsr update_palette
+
 skipped:
 
     clc