fixed pixel order, added LARGE option

[a2gs_xortest] / xortest.s

diff --git a/xortest.s b/xortest.s
index b876059..9a32dc2 100644 (file)
--- a/xortest.s
+++ b/xortest.s
@@ -1,5 +1,7 @@
        org $800
 
+LARGE = 0
+
 REG_NEWVID = $c029
 FB_BASE        = $e12000
 
@@ -12,15 +14,15 @@ FB_BASE     = $e12000
        rep #$30        ; accum/index 16bit
        lda #$0000
        ldx #$0000
-fillrest
+fillrest               ; @30f
        stal $e19d00,x
        inx
        inx
-       cpx #$300
+       cpx #$100
        bne fillrest
        
        lda #$0000
-cmap   pha
+cmap   pha             ; @31d
        sta 0
        asl
        tax     ; offset = i * 2
@@ -38,29 +40,53 @@ cmap        pha
        bne cmap
 
 YVAL   = 0
-COLIDX = 1
+TMPVAL = 1
+YNIB   = 2
 
-       sep #$20        ; accum 8bit
-       ldx #0          ; fb index
+       sep #$20        ; accum 8bit  @337
+       ldx #0000       ; fb index
        stz YVAL
-yloop  lda YVAL
-       and #$f
-       sta COLIDX
+yloop  ldy #0000       ; column/2 on Y reg  @33e
+xloop  lda YVAL        ; @341
+
+       DO LARGE
+       lsr
+       FIN
+
+       and #$0f
+       sta YNIB
+       tya
+
+       DO LARGE = 0
        asl
+       inc             ; increment X, next pixel on low nibble
+       FIN
+
+       and #$0f
+       sta TMPVAL      ; save first pixel X coordinate
+
+       DO LARGE = 0
+       dec             ; decrement back for high nibble pixel
+       FIN
+
+       eor YNIB
+       asl             ; move next pixel value to high nibble
        asl
        asl
        asl
-       ora COLIDX
-       ldy #160        ; 160 bytes across
-xloop  stal FB_BASE,x
+       ora TMPVAL      ; first pixel X -> low nibble
+       eor YNIB
+
+       stal FB_BASE, x ; write the pixel pair
        inx
-       dey
+       iny
+       cpy #160
        bne xloop
        inc YVAL
        lda YVAL
        cmp #200
        bne yloop
 
-infloop        bra infloop
+infloop        bra infloop     ; @36d
 
        ; vi:ft=asm_ca65