change code to deal with offsets from grid rather than addressing scren

memory directly from the get go

- this is so i can just store the current offset and modify the previous
  generation and current generation in one go than changing two separate
  variables

1 files changed, 56 insertions, 15 deletions

diff --git a/life.asm b/life.asm
index 44e3996..5544272 100644
--- a/life.asm
+++ b/life.asm
@@ -3,12 +3,16 @@
 
 numL := $02 ; low byte of a 16-bit number
 numH := $03 ; low byte of a 16-bit number
-key_buf_len := $c6
-key_buf := $0277
+num2L := $04
+num2H := $05
 GETIN := $ffe4
 CHROUT := $ffd2
 CLRCHN := $e544
 
+; one byte for each cell, 1000 bytes because 40x25 screen; is identical to
+; screen memory (i.e. $a0 is alive and $20 is dead)
+prev_grid := $0801
+
 ; initialisation: clear screen and set num to point to screen mem start
 init:
   ; clear screen
@@ -16,14 +20,14 @@ init:
   jsr CHROUT
 
   ldy #$00
-  lda #$04
-  sta numH
   lda #$00
+  sta numH
   sta numL
   jsr CLRCHN
   jmp loop
 
 ; main loop
+; num stores offset from grid
 loop:
   jsr GETIN
   beq loop
@@ -68,8 +72,15 @@ if_reset:
   jmp loop
 
 if_space:
-  ldx #$00
-  lda (numL,x)
+  lda numL
+  sta num2L
+  lda numH
+  clc
+  adc #$04
+  sta num2H
+
+  ldy #$00
+  lda (num2L),y
   cmp #$a0
   beq if_cell_filled
   jmp if_cell_empty
@@ -82,21 +93,23 @@ if_cell_empty:
   jsr print_byte
   jmp loop
 
-; print byte in A at location in num
+; print byte in A at location in screen_mem+num; destroys Y; num2 is expected
+; to be $0400 (screen_mem zero location) and is set to that at the end
 print_byte:
-  ; init: store original A in X and push Y to stack
-  tax
-  tya
+  tay
+  lda numH
   pha
-  txa
 
+  clc
+  adc #$04
+  sta numH
+
+  tya
   ldy #$00
   sta (numL),y
 
-  ; deinit: pull Y from stack and transfer original A from X to A
   pla
-  tay
-  txa
+  sta numH
   rts
 
 ; adds A to num
@@ -109,7 +122,17 @@ a16b:
   sta numH
   rts
 
-; subtracts A from num
+; adds A to num2
+a16b2:
+  clc
+  adc num2L
+  sta num2L
+  lda #$00
+  adc num2H
+  sta num2H
+  rts
+
+; subtracts A from num (destroys X)
 s16b:
   pha
   lda numL
@@ -124,6 +147,24 @@ s16b:
   pla
   rts
 
+; might change functions to take from stack but this is easier for now as I
+; only have 2 16 bit numbers to deal with anyways
+
+; subtracts A from num2 (destroys X)
+s16b2:
+  pha
+  lda num2L
+  tsx
+  inx
+  sec
+  sbc $0100,x
+  sta num2L
+  lda num2H
+  sbc #$00
+  sta num2H
+  pla
+  rts
+
 inc_num:
   inc numL
   beq inc_H