nibbles/nibbles.S

#define WIDTH 60
#define HEIGHT 40

.bss
// Array of longs representing the game field
.align 4
world:			.space WIDTH*HEIGHT*4

.data
// Current length of the snake
snakeLength: 	.long 0
// Snake position
snakePosX:		.long WIDTH / 2
snakePosY:		.long HEIGHT / 2
// Snake direction
snakeDirX:		.long 1
snakeDirY:		.long 0
// Number of apples
numApples:		.long 0
// Optional score-keeping
score: 			.long 0
// Utility strings
snibbles: 		.ascii "NIBBLES"
snibbles_end:
sgameover: 		.string " Game over! Score: %i "
sgameover_end:
string1:		.string "Started with snake length %i and %i apples!\n"
string2:		.string "Snake position: (%i, %i)\n"
stringi:		.string "%i\n"
stringtest:		.string "> %i %i %c\n"

.text
.global start_game
start_game:
	// snakeLength = len
	movl 4(%esp), %eax
	movl %eax, snakeLength
	// numApples = n_apples
	movl 8(%esp), %eax
	movl %eax, numApples

	pushl %ebx
	pushl %edi
	
	// Call nib_init
	call nib_init
	// Seed randomness
	pushl $0
	call time
	addl $4, %esp
	pushl %eax
	call srand
	addl $4, %esp

	// Print our arguments
	//pushl numApples
	//pushl snakeLength
	//pushl $string1
	//call printf
	//addl $4*3, %esp

	// Print worm position
	//pushl snakePosY
	//pushl snakePosX
	//pushl $string2
	//call printf
	//addl $4*3, %esp

	// Initialize the snake array
	// Set every cell to a time value greater than the snake length
	movl $world, %edi
	movl snakeLength, %eax
	movl $WIDTH*HEIGHT, %ebx
	xorl %ecx, %ecx
1:
	movl %eax, (%edi, %ecx, 4)
	incl %ecx
	cmpl %ebx, %ecx
	jl 1b

	// Spawn initial apples
	movl numApples, %ecx
1:
	pushl %ecx
	call spawnApple
	popl %ecx
	loop 1b

	// Loop forever
loop:
	// Sleep for a while
	pushl $250*1000
	pushl %ecx
	call usleep
	addl $4, %esp

	jmp tick

	popl %edi
	popl %ebx
	ret

// Update stuff
tick:
	movl $world, %edi
	
	// Increment cell times
	movl snakeLength, %ebx
	xorl %ecx, %ecx
1:
	movl (%edi, %ecx, 4), %eax
	// If the value is negative it's an apple we don't want to disappear
	test %eax, %eax
	js 2f
	// No need to increment if it's already greater than snakeLength
	cmpl %ebx, %eax
	jg 2f
	// Increment the cell value
	incl %eax
	movl %eax, (%edi, %ecx, 4)
2:	incl %ecx // Loop increment
	cmpl $WIDTH*HEIGHT, %ecx
	jne 1b
	
	// Input
	call nib_poll_kbd
	// Down
	movl $258, %ebx
	cmpl %eax, %ebx
	jne 1f
	movl $0, snakeDirX
	movl $1, snakeDirY
1: 	// Up
	movl $259, %ebx
	cmpl %eax, %ebx
	jne 1f
	movl $0, snakeDirX
	movl $-1, snakeDirY
1: 	// Left
	movl $260, %ebx
	cmpl %eax, %ebx
	jne 1f
	movl $-1, snakeDirX
	movl $0, snakeDirY
1: 	// Right
	movl $261, %ebx
	cmpl %eax, %ebx
	jne 1f
	movl $1, snakeDirX
	movl $0, snakeDirY
1:

	// Move snake
	// snakePosX = (snakePosX + snakeDirY + WIDTH) % WIDTH
	movl snakePosX, %eax
	movl snakeDirX, %ebx
	addl %ebx, %eax
	addl $WIDTH, %eax // For modulo wrap-around
	xorl %edx, %edx
	movl $WIDTH, %ecx 
	divl %ecx
	mov %edx, snakePosX
	// snakePosY = (snakePosY + snakeDirY + HEIGHT) % HEIGHT
	movl snakePosY, %eax
	movl snakeDirY, %ebx
	addl %ebx, %eax
	addl $HEIGHT, %eax // For modulo wrap-around
	xorl %edx, %edx
	movl $HEIGHT, %ecx 
	divl %ecx
	mov %edx, snakePosY

	// Get value at head position
	movl snakePosY, %eax
	movl $WIDTH, %edx
	mull %edx
	addl snakePosX, %eax
	movl (%edi, %eax, 4), %edx

	// Collision with apple if negative
	test %edx, %edx
	js 1f
	// No need to increment if it's already greater than snakeLength
	movl snakeLength, %ebx
	cmpl %ebx, %edx
	jg 2f
	// End the game when the snake collides with itself
	jmp gameOver
1:	// Spawn a new apple
	pushl %edi
	pushl %eax
	call spawnApple
	popl %eax
	popl %edi
	// Extend the snake!
	incl snakeLength
2:

	// Set time value to 0 at snake head position
	// i = x + y * WIDTH
	// %edi = %ebx + %ecx * $WIDTH
	movl $0, (%edi, %eax, 4)

	jmp draw
	//jmp debug_draw

// Draw stuff
draw:
	// Loop Y
	movl $HEIGHT, %ecx
1:
	// Loop X
	movl $WIDTH, %ebx
2:
	// Save loop registers
	pushl %ecx
	pushl %ebx
	subl $1, %ecx
	subl $1, %ebx

	// Call nib_put_scr

	// i = x + y * WIDTH
	// %eax = %ebx + %ecx * $WIDTH
	movl %ecx, %eax
	movl $WIDTH, %edx
	mull %edx
	addl %ebx, %eax
	// Fetch the value of the cell
	movl $world, %edi
	movl (%edi, %eax, 4), %eax
	
	// Compare with the snake length
	cmpl snakeLength, %eax
	// If the value is negative, it's an apple
	test %eax, %eax
	js 4f
	// If it's greater or equal to snakeLength, it's empty
	cmpl snakeLength, %eax
	jge 3f
	// Else, it's part of the snake
	pushl $'@'
	jmp 5f
3:	pushl $' '
	jmp 5f
4:	pushl $'o'
5:

	movl %ecx, %eax // Y
	pushl %eax 
	
	movl %ebx, %eax // X
	pushl %eax
	
	call nib_put_scr
	addl $4*3, %esp

	// Restore loop registers
	popl %ebx
	popl %ecx

	decl %ebx // Decrement X
	jnz 2b // End of X loop
	loop 1b // End of Y loop

	jmp loop

// Debug drawing
debug_draw:
	// Loop Y
	movl $HEIGHT, %ecx
1:
	// Loop X
	movl $WIDTH, %ebx
2:
	// Save loop registers
	pushl %ecx
	pushl %ebx
	subl $1, %ecx
	subl $1, %ebx

	// Call nib_put_scr

	// i = x + y * WIDTH
	// %edi = %ebx + %ecx * $WIDTH
	movl %ecx, %eax
	movl $WIDTH, %edx
	mull %edx
	addl %ebx, %eax
	// Fetch the value of the cell
	movl $world, %edi
	movl (%edi, %eax, 4), %eax	
	pushl %eax

	movl %ecx, %eax // Y
	pushl %eax 
	
	movl %ebx, %eax // X
	pushl %eax
	
	call nib_put_scr
	addl $4*3, %esp

	// Restore loop registers
	popl %ebx
	popl %ecx

	decl %ebx // Decrement X
	jnz 2b // End of X loop
	loop 1b // End of Y loop

	jmp loop

gameOver:
	// Calculate string length
	movl $sgameover_end, %eax
	subl $sgameover, %eax
	subl $1, %eax // Discount null terminator

	// Calculate X-pos
	movl $2, %ebx
	xorl %edx, %edx
	divl %ebx
	negl %eax
	addl $WIDTH/2, %eax

	// Print game over message
	pushl snakeLength
	pushl $sgameover
	pushl %eax // X
	pushl $HEIGHT/2 // Y
	call mvprintw
	add $4*3, %esp
	call refresh

	pushl $3000*1000
	call usleep
	addl $4, %esp
	call nib_end

spawnApple:
	pushl %ebx

	// %ecx = rand() % HEIGHT
	call rand
	xorl %edx, %edx
	movl $HEIGHT, %ebx 
	divl %ebx
	movl %edx, %ecx
	// %ebx = rand() % WIDTH
	pushl %ecx
	call rand
	xorl %edx, %edx
	movl $WIDTH, %ebx 
	divl %ebx
	movl %edx, %ebx
	popl %ecx

	// i = x + y * WIDTH
	// %eax = %ebx + %ecx * $WIDTH
	movl %ecx, %eax
	movl $WIDTH, %edx
	mull %edx
	addl %ebx, %eax

	// Set the cell negative to represent an apple
	movl $world, %ecx
	movl $-1, %edx
	movl %edx, (%ecx, %eax, 4)

	popl %ebx
	ret