work in progress

.gitignore

@@ -0,0 +1,5 @@
+.DS_Store
+*.o
+*.xex
+*.pxd
+canvas*.png

dither4.js

@@ -530,9 +530,12 @@ function decimate(input, palette, n) {
         let least = Infinity;
         let pick = -1;
         for (let i = 1; i < decimated.length; i++) {
-            if (i == 0) {
+            if (decimated[i] === palette256[0]) {
                 continue; // keep black always
             }
+            if (decimated[i] === palette256[0x0f]) {
+                continue; // keep white always
+            }
 
             //let coolFactor = popularity[i];
 
@@ -552,11 +555,15 @@ function decimate(input, palette, n) {
             }
         }
         let old = decimated.length;
+        //decimated.splice(pick, 1);
         decimated = decimated.filter((rgb, i) => {
             if (i == pick) {
                 return false;
             }
-            if (i > 0 && popularity[i] == 0) {
+            if (rgb !== palette256[0] && popularity[i] == 0) {
+                return false;
+            }
+            if (rgb !== palette256[0x0f] && popularity[i] == 0) {
                 return false;
             }
             return true;

dither4.s

@@ -1,23 +1,91 @@
 SAVMSC = $58
+SDMCTL = $22F
+SDLSTL = $230
+SDLSTH = $231
+COLPF0 = $D016
+COLPF1 = $D017
+COLPF2 = $D018
+COLPF3 = $D019
+COLBK = $D01A
+
+WSYNC = $D40A
+VCOUNT = $D40B
+NMIEN = $D40E
+
+.data
+
+.import palette1
+.import palette2
+.import palette3
+.import framebuffer
+
+displaylist:
+    .repeat 3
+        .byte $70 ; 8 blank lines
+    .endrep
+    .byte $4e ; ANTIC mode e (160px 2bpp, 1 scan line per line)
+    .addr framebuffer
+    .repeat 191
+        .byte $0e
+    .endrep
+    .byte $41 ; jump and blank
+    .addr displaylist
+
 
 .code
 
 .export start
 
-.proc start
+; Loop through scan lines updating the palette
-    ; Get the framebuffer address and just write new fun values into it
+.proc update_palette
-    ; x: byte to write in
+    lda palette1,y
-    ; y: index into the first 256 bytes of buffer
+    pha
+    ldx palette2,y
+    lda palette3,y
+    tay
+    pla
+
+    ; Wait for horizontal blank
+    sta WSYNC
+
+    ; Update color registers as fast as possible
+    sta COLPF0
+    stx COLPF1
+    sty COLPF2
+    rst
+.endproc
+
+.proc start
+    ; Disable display DMA
+    lda #$00
+    sta SDMCTL
+    ; Set up the display list
+    lda .low displaylist
+    sta SDLSTL
+    lda .high displaylist
+    sta SDLSTH
+
+    ; Turn off interrupts except reset button
+    lda #$20
+    sta NMIEN
+
+    ; Manually wait for first scan line
+wait_vblank:
+    lda VCOUNT
+    bnz wait_vblank
+
+    ; Re-enable display DMA
+    lda #$22
+    sta SDMCTL
+
+even_scanline:
+    ldy VCOUNT
+    jsr update_palette
+
+odd_scanline:
+    ldy VCOUNT
+    iny
+    jsr update_palette
+    jmp even_scanline
 
-    ldx #00
-outer_loop:
-    txa
-    ldy #00
-inner_loop:
-    sta (SAVMSC),y
-    iny
-    bne inner_loop
-    inx
-    jmp outer_loop
-    ; infinite loop
 .endproc