fix flickering

[lifeboot.git] / lifeboot.asm

diff --git a/lifeboot.asm b/lifeboot.asm
index 0e114d0a7a93aebfb29ace065599d1129d3fd84e..655febbd6ab1d07658e013e5705f4455a728dd6f 100644 (file)
--- a/lifeboot.asm
+++ b/lifeboot.asm
@@ -14,7 +14,7 @@ org 0x7c00
 
 %define COLS 80
 %define ROWS 25
-%define VGAPGSZ (COLS * ROWS * 2)
+%define VGAPGSZ (COLS * ROWS * 2 + 96)  ; why 96 ??????
 
 ; memory layout ---------------------------------------------------------------
 
@@ -33,10 +33,10 @@ org 0x7c00
 
 ; initialize segment registers
 mov ax, VGA >> 4
-mov ds, ax
 mov es, ax
 
 xor ax, ax
+mov ds, ax
 mov ss, ax
 
 ; set stack pointers
@@ -52,22 +52,36 @@ mov ah, 0x01                ; set text-mode cursor shape
 int 0x10                    ; video services
 
 ; initialize xss
+
+set_xss_seed:
+
 mov ah, 0x00                ; get
 int 0x1a                    ;  system time
+
+cmp dx, 0
+je set_xss_seed             ; if seed is 0, xs wont work properly
+
 mov [xss], dx               ; cx:dx = number of clock ticks since midnight
 
 ; initialize currvgapg
-mov word [currvgapg], VGAPGSZ
+mov word [currvgapg], 0
 
-; setup -----------------------------------------------------------------------
+; start simulation from random state ------------------------------------------
 
-setup:
+start:
 
 call init_grid
+
+; apply game of life's rules to determine the next state ----------------------
+
+next_state:
+
+call vsync_wait
+call write_next_vga_page
+call wait_keypress
 call flip_vga_page
-call delay
 
-jmp setup
+jmp next_state
 
 ; =============================================================================
 
@@ -87,6 +101,17 @@ int 0x15                    ; wait
 
 ret
 
+; wait_keypress() - wait for any keypress -------------------------------------
+
+; clobbers: ax
+
+wait_keypress:
+
+mov ah, 0x00        ; read key press
+int 0x16            ; keyboard services
+
+ret
+
 ; vsync_wait() - wait for display to enter the next VBlank cycle --------------
 
 ; clobbers ax, dx
@@ -175,6 +200,162 @@ int 0x10                    ; video services
 
 ret
 
+; alive_neighbours() ----------------------------------------------------------
+
+; input:
+; es:si     -> current grid
+; cx        -> cell index
+
+; output:
+; ax = # alive neighbours
+
+; clobbers ax, bx, dx
+
+alive_neighbours:
+enter 5, 0
+
+; [bp - 1]: row
+; [bp - 2]: col
+; [bp - 3]: neighbours
+; [bp - 4]: i
+; [bp - 5]: j
+
+mov ax, cx                  ; ax = idx
+mov bl, COLS                ; bl = COLS
+div bl                      ; al = idx / COLS ; ah = idx % COLS
+
+mov [bp - 1], al            ; row = idx / COLS
+mov [bp - 2], ah            ; row = idx % COLS
+mov byte [bp - 3], 0        ; neighbours = 0
+
+mov byte [bp - 4], -1       ; i = -1
+.i:                         ; do {
+
+    mov byte [bp - 5], -1           ; j = -1
+.j:                                 ; do {
+
+        mov al, [bp - 4]
+        or al, [bp - 5]
+        jz .continue                    ; if (!i && !j) continue
+
+        mov al, [bp - 1]
+        add al, [bp - 4]                ; al = row + i
+
+        cmp al, 0
+        jl .continue                    ; if (row + i < 0) continue
+
+        cmp al, ROWS
+        jge .continue                   ; if (row + i >= ROWS) continue
+
+        mov ah, [bp - 2]
+        add ah, [bp - 5]                ; ah = col + j
+
+        cmp ah, 0
+        jl .continue                    ; if (col + j < 0) continue
+
+        cmp ah, COLS
+        jge .continue                   ; if (col + j >= COLS) continue
+
+        movzx bx, ah                    ; bx = col + j
+
+        mov ah, COLS
+        mul ah                          ; ax = (row + i) * COLS
+
+        add bx, ax                      ; bx = cell index
+        shl bx, 1                       ; bx = grid offset
+
+        mov dx, [es:si + bx]            ; dl = cell state
+
+        cmp dl, ALIVE                   ; if (!ALIVE) continue
+        jne .continue
+
+        inc byte [bp - 3]               ; neighbours++
+
+.continue:
+        inc byte [bp - 5]
+        cmp byte [bp - 5], 1
+        jle .j                      ; } while (++j <= 1)
+
+    inc byte [bp - 4]
+    cmp byte [bp - 4], 1
+    jle .i                  ; } while (++i <= 1)
+
+movzx ax, byte [bp - 3]     ; ax = # alive neighbours
+
+leave
+ret
+
+; write_next_cell_state() -----------------------------------------------------
+
+; input:
+; es:si     -> current grid
+; es:di     -> next grid
+; cx        -> cell index
+
+; output:
+; [es:di + cx * 2] = updated cell state
+
+; clobbers ax, bx, dx
+
+write_next_cell_state:
+
+call alive_neighbours       ; ax = # alive neighbours
+
+mov bx, cx
+shl bx, 1
+
+mov dx, [es:si + bx]        ; dl = cell current state
+
+cmp dl, ALIVE               ; if (ALIVE) {
+jne .else
+
+cmp ax, 2                   ;     if (n < 2)
+jl .dead                    ;         return DEAD
+
+cmp ax, 3                   ;     if (n > 3)
+jg .dead                    ;         return DEAD
+
+jmp .alive                  ;     return ALIVE
+
+.else:                      ; }
+
+cmp ax, 3                   ; if (n != 3)
+jne .dead                   ;     return DEAD
+
+.alive:                     ; return ALIVE
+mov dl, ALIVE
+jmp .write
+
+.dead:
+mov dl, DEAD
+
+.write:
+mov [es:di + bx], dx
+
+ret
+
+; write_next_vga_page() -------------------------------------------------------
+
+; clobbers di, si, ax, bx, cx, dx
+
+write_next_vga_page:
+
+mov si, [currvgapg]         ; es:si -> current page
+
+mov di, VGAPGSZ
+xor di, si                  ; es:di -> next page
+
+xor cx, cx                  ; i = 0
+
+.update_loop:
+call write_next_cell_state
+
+inc cx
+cmp cx, COLS * ROWS
+jl .update_loop             ; for i in [0 .. COLS * ROWS - 1]
+
+ret
+
 ; halt() - stop program execution ---------------------------------------------
 
 halt: