From 529c34efef580066b41156556bf3fe7668ddf97a Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Fri, 15 Mar 2013 14:59:12 +0100
Subject: Reverse play field, prevent death by going backwards

---
 snake.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/snake.c b/snake.c
index 2b87327..22011f8 100644
--- a/snake.c
+++ b/snake.c
@@ -20,10 +20,11 @@ typedef enum _dir_t {
 } dir_t;
 
 
-static volatile uint8_t dir;
-static volatile bool start = false;
+static volatile uint8_t kbdir;
+static volatile bool start;
 static volatile uint16_t lfsr = 0xace1;
 
+static uint8_t dir;
 static point_t tail = {7, 4};
 
 #define HISTORY_MAX 128
@@ -88,7 +89,7 @@ static void reset(void) {
 
 	rand_q();
 
-	dir = EAST;
+	kbdir = dir = EAST;
 	tail = (point_t){7, 4};
 	history_len = 0;
 	history_pos = 0;
@@ -98,6 +99,10 @@ static void reset(void) {
 		move(EAST, true);
 }
 
+static void set_led(uint8_t x, uint8_t y, uint8_t val) {
+	LedSignSet(13-x, 8-y, val);
+}
+
 void kbd_handle(uint16_t code, bool make) {
 	if (!make)
 		return;
@@ -108,19 +113,19 @@ void kbd_handle(uint16_t code, bool make) {
 		break;
 
 	case KBD_CODE_UP:
-		dir = NORTH;
+		kbdir = NORTH;
 		break;
 
 	case KBD_CODE_LEFT:
-		dir = WEST;
+		kbdir = WEST;
 		break;
 
 	case KBD_CODE_DOWN:
-		dir = SOUTH;
+		kbdir = SOUTH;
 		break;
 
 	case KBD_CODE_RIGHT:
-		dir = EAST;
+		kbdir = EAST;
 	}
 }
 
@@ -155,24 +160,27 @@ static bool point_used(const point_t *p, bool head) {
 }
 
 static bool step(void) {
+	if (kbdir != rev(dir))
+		dir = kbdir;
+
 	uint8_t d = dir;
 
 	rand_mix(d);
 
-	LedSignSet(tail.x, tail.y, 0);
+	set_led(tail.x, tail.y, 0);
 
 	int i;
 	point_t pt = tail;
 
-	LedSignSet(pt.x, pt.y, 0);
+	set_led(pt.x, pt.y, 0);
 
 	for (i = 0; i < history_len; i++) {
 		go(&pt, get_dir(i));
-		LedSignSet(pt.x, pt.y, 2);
+		set_led(pt.x, pt.y, 2);
 	}
 
 	go(&pt, d);
-	LedSignSet(pt.x, pt.y, 3);
+	set_led(pt.x, pt.y, 3);
 
 	if (point_used(&pt, true))
 		return false;
@@ -189,7 +197,7 @@ static bool step(void) {
 	if (point_used(&pt, false))
 		return false;
 
-	LedSignSet(q.x, q.y, 7);
+	set_led(q.x, q.y, 7);
 
 	return true;
 }
@@ -203,9 +211,8 @@ int main() {
 	kbd_send(KBD_CMD_RESET);
 
 	while(true) {
-		while (!start) {}
 		start = false;
-
+		while (!start) {}
 		reset();
 
 		while (step())
-- 
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