snake

1 files changed, 118 insertions, 46 deletions

diff --git a/fw/snake.c b/fw/snake.c
index 968379e..a57d241 100644
--- a/fw/snake.c
+++ b/fw/snake.c
@@ -6,23 +6,27 @@ __sfr __at(0x70) UART_TX;
 __sfr __at(0x71) UART_RX;
 __sfr __at(0x72) UART_STATUS;
 
-/*
- * how many OVF per refresh of the screen
- */
-#define OVF_PER_REFRESH 80
+#define GRID_W       20
+#define GRID_H       10
+#define MAX_LEN      20
+#define OVF_PER_FRAME 60
 
 #define DIR_UP    0
 #define DIR_DOWN  1
 #define DIR_LEFT  2
 #define DIR_RIGHT 3
 
-uint8_t direction;
-uint8_t position[2];
-
-static volatile uint8_t ovf_count = 0;
+static uint8_t snake_x[MAX_LEN];
+static uint8_t snake_y[MAX_LEN];
+static uint8_t snake_len;
+static uint8_t direction;
+static uint8_t food_x;
+static uint8_t food_y;
+static uint8_t score;
+static volatile uint8_t ovf_count;
 
 void isr(void) __interrupt(0) {
-    if (INTCON & 0x04) {        /* T0IF = bit 2 */
+    if (INTCON & 0x04) {
         ovf_count++;
         INTCON &= ~(uint8_t)0x04;
     }
@@ -39,8 +43,8 @@ static void uart_puts(const char *s) {
 
 static uint8_t uart_recv(void) {
     if (UART_STATUS & 0x02)
-        return 0;           /* rx_empty: nothing to read */
-    return UART_RX;         /* reading pops the FIFO */
+        return 0;
+    return UART_RX;
 }
 
 static uint8_t uart_getc(void) {
@@ -50,25 +54,19 @@ static uint8_t uart_getc(void) {
 
 static void handle_input(void) {
     uint8_t c = uart_recv();
-    if (c != 0x1B)
-        return;
-    if (uart_getc() != '[')
-        return;
+    if (c != 0x1B) return;
+    if (uart_getc() != '[') return;
     switch (uart_getc()) {
-        case 'A': direction = DIR_UP;    break;  /* ESC [ A */
-        case 'B': direction = DIR_DOWN;  break;  /* ESC [ B */
-        case 'C': direction = DIR_RIGHT; break;  /* ESC [ C */
-        case 'D': direction = DIR_LEFT;  break;  /* ESC [ D */
+        case 'A': if (direction != DIR_DOWN)  direction = DIR_UP;    break;
+        case 'B': if (direction != DIR_UP)    direction = DIR_DOWN;  break;
+        case 'C': if (direction != DIR_LEFT)  direction = DIR_RIGHT; break;
+        case 'D': if (direction != DIR_RIGHT) direction = DIR_LEFT;  break;
     }
 }
 
-static void update_position(void) {
-    switch (direction) {
-        case DIR_UP:    position[1]--; break;
-        case DIR_DOWN:  position[1]++; break;
-        case DIR_LEFT:  position[0]--; break;
-        case DIR_RIGHT: position[0]++; break;
-    }
+static void place_food(void) {
+    food_x = (ovf_count * 7 + 3) % GRID_W;
+    food_y = (ovf_count * 5 + 1) % GRID_H;
 }
 
 static void print_uint8(uint8_t v) {
@@ -83,40 +81,114 @@ static void print_uint8(uint8_t v) {
     uart_send(v + '0');
 }
 
-
 static void render(void) {
-    uart_puts("\x1B[H");   /* cursor home */
+    uint8_t x, y, i;
+
+    uart_puts("\x1B[H");
 
-    uart_puts("pos: ");
-    print_uint8(position[0]);
-    uart_puts(", ");
-    print_uint8(position[1]);
-    uart_puts("\r\n");
+    /* top border */
+    uart_send('+');
+    for (x = 0; x < GRID_W; x++) uart_send('-');
+    uart_puts("+\r\n");
+
+    for (y = 0; y < GRID_H; y++) {
+        uart_send('|');
+        for (x = 0; x < GRID_W; x++) {
+            uint8_t ch = ' ';
+            if (x == food_x && y == food_y) {
+                ch = '*';
+            } else {
+                for (i = 0; i < snake_len; i++) {
+                    if (snake_x[i] == x && snake_y[i] == y) {
+                        ch = (i == 0) ? 'O' : 'o';
+                        break;
+                    }
+                }
+            }
+            uart_send(ch);
+        }
+        uart_puts("|\r\n");
+    }
+
+    /* bottom border */
+    uart_send('+');
+    for (x = 0; x < GRID_W; x++) uart_send('-');
+    uart_puts("+\r\n");
+
+    uart_puts("Score: ");
+    print_uint8(score);
+    uart_puts("   \r\n");
 }
 
+/* returns 1 if alive, 0 if dead */
+static uint8_t update(void) {
+    uint8_t nx, ny, i;
+
+    nx = snake_x[0];
+    ny = snake_y[0];
+    switch (direction) {
+        case DIR_UP:    if (ny == 0)         return 0; ny--; break;
+        case DIR_DOWN:  if (ny == GRID_H-1)  return 0; ny++; break;
+        case DIR_LEFT:  if (nx == 0)         return 0; nx--; break;
+        case DIR_RIGHT: if (nx == GRID_W-1)  return 0; nx++; break;
+    }
+
+    /* self-collision (exclude tail: it moves away this step) */
+    for (i = 0; i < snake_len - 1; i++) {
+        if (snake_x[i] == nx && snake_y[i] == ny) return 0;
+    }
+
+    if (nx == food_x && ny == food_y) {
+        if (snake_len < MAX_LEN) snake_len++;
+        score++;
+        place_food();
+    }
+
+    /* shift body back, add new head */
+    for (i = snake_len - 1; i > 0; i--) {
+        snake_x[i] = snake_x[i-1];
+        snake_y[i] = snake_y[i-1];
+    }
+    snake_x[0] = nx;
+    snake_y[0] = ny;
+
+    return 1;
+}
 
 void main(void) {
+    uint8_t alive;
 
     OPTION_REG = 0x07;
     TMR0 = 0;
     INTCON = 0xa0;
 
-    direction = DIR_RIGHT;
-    position[0] = 10;
-    position[1] = 5;
+    while (1) {
+        /* init */
+        direction  = DIR_RIGHT;
+        snake_len  = 3;
+        score      = 0;
+        snake_x[0] = 5; snake_y[0] = 5;
+        snake_x[1] = 4; snake_y[1] = 5;
+        snake_x[2] = 3; snake_y[2] = 5;
+        place_food();
 
-    uart_puts("\x1B[2J\x1B[H");
-    uart_puts("snake\r\n");
-    uart_puts("-----------\r\n");
+        uart_puts("\x1B[2J\x1B[H");
 
-    while (1) {
-        ovf_count = 0;
-        while (ovf_count < OVF_PER_REFRESH);
+        alive = 1;
+        while (alive) {
+            ovf_count = 0;
+            while (ovf_count < OVF_PER_FRAME);
 
-        handle_input();
-        update_position();
-        render();
+            handle_input();
+            alive = update();
+            render();
+            PORTA ^= 0x01;
+        }
 
-        PORTA ^= 0x01;
+        uart_puts("\x1B[2J\x1B[H");
+        uart_puts("GAME OVER  score: ");
+        print_uint8(score);
+        uart_puts("\r\npress any key\r\n");
+        uart_getc();
     }
 }