add basic cell modifying

1 files changed, 27 insertions, 18 deletions

diff --git a/life.asm b/life.asm
index b8e9fd0..1e3a6af 100644
--- a/life.asm
+++ b/life.asm
@@ -23,39 +23,49 @@ loop:
 
   cmp #$1d ; right arrow
   beq if_right
-
   cmp #$9d ; left arrow
   beq if_left
-  jmp else_left
-if_left:
-  jsr dec_num
-  jmp loop
-else_left:
+  cmp #$2d ; reset if - pressed
+  beq if_reset
+  cmp #$20 ; fill cell if space pressed
+  beq if_space
+  cmp #$30 ; end program if 0 pressed
+  bne loop
+  jmp end
 
-  jsr print_byte
 if_right:
   jsr inc_num
+  jmp loop
+
+if_left:
+  jsr dec_num
+  jmp loop
 
-  cmp #$2d ; reset if - pressed
-  beq if_reset
-  jmp else_reset
 if_reset:
-  pha
   lda #$04
   sta numH
   lda #$00
   sta numL
-  pla
   jmp loop
 
-else_reset:
-  cmp #$30 ; end program if 0 pressed
-  bne loop
-  jmp end
+if_space:
+  ldx #$00
+  lda (numL,x)
+  cmp #$a0
+  beq if_cell_filled
+  jmp if_cell_empty
+if_cell_filled:
+  lda #$20
+  jsr print_byte
+  jmp loop
+if_cell_empty:
+  lda #$a0
+  jsr print_byte
+  jmp loop
+
 
 ; loops until keyboard buffer has any number of characters in it
 key_wait:
-  ; init: pha to retrieve before rts, to keep A intact
   pha
 key_wait_loop:
   lda key_buf_len ; shows how many keys are in key buffer
@@ -105,7 +115,6 @@ print_byte:
   txa
 
   ldy #$00
-  sbc #$3f ; convert (very vaguely) to c64 screen codes
   sta (numL),y
 
   ; deinit: pull Y from stack and transfer original A from X to A