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Prevent the snake from going back on itself #3

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60 changes: 33 additions & 27 deletions snake.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,9 @@ using namespace blit;
const uint32_t UPDATE_RATE = 200;

// Some handy constants for movement directions and "stopped" state
const Vec2 MOVE_UP(0, -1);
const Vec2 MOVE_DOWN(0, 1);
const Vec2 MOVE_LEFT(-1, 0);
const Vec2 MOVE_RIGHT(1, 0);
const Vec2 STOP(0, 0);
enum Direction {
Up, Down, Left, Right, Stop
};

// These points index into the spritesheet, using x/y values
// makes it easy to identify a specific sprite.
Expand All @@ -30,7 +28,8 @@ const uint32_t NUM_SPRITES = 14; // First 14 sprites on the top row
Rect game_bounds;

// Current snake direction
Vec2 direction(0, 0);
Direction direction = Stop;
Direction last_move = Stop;

// The snake itself is a vector of Points
std::vector<Point> snake;
Expand All @@ -53,7 +52,7 @@ void restart_game() {
// Remove all snake
snake.clear();
snake.emplace_back(game_bounds.center());
direction = STOP;
direction = Stop;
score = 0;
random_reset();
apple = get_random_point(game_bounds.size());
Expand All @@ -64,11 +63,27 @@ void restart_game() {
// this allows us to run the game at a speed (more or less) of our choosing.
// TASK you could try making Snake harder over time by speeding it up!
void move(Timer &t) {
// No movement means nothing to do here
// exit early so the snake doesn't continually collide with itself
if (direction == Vec2(0.0f, 0.0f)) return;

Point head = snake.back() + direction;
Point head = snake.back();
switch(direction) {
case Up:
head.y -= 1;
break;
case Down:
head.y += 1;
break;
case Left:
head.x -= 1;
break;
case Right:
head.x += 1;
break;
default:
// No movement means nothing to do here
// exit early so the snake doesn't continually collide with itself
return;
}

for(auto segment : snake) {
// If the head x/y coordinates match any body/segment
// coordinates then we've collided with ourselves. BAD LUCK!
Expand Down Expand Up @@ -99,6 +114,7 @@ void move(Timer &t) {
// which is A BAD THING, but for the sake of snake... it's fiiiinnnee!
snake.erase(snake.begin());
}
last_move = direction;
}

void init() {
Expand Down Expand Up @@ -150,20 +166,10 @@ void render(uint32_t time_ms) {

void update(uint32_t time) {
// Movement is easy. You can't go back on yourself.
// These checks ensure you can't be moving left,
// ie: directon.x == -1
// and change direction to go back over yourself,
// ie: direction.x == 1
if(direction.x == 0) {
// If we're not already moving along the X axis,
// allow a change in direction along X
if(buttons.pressed & DPAD_RIGHT) direction = MOVE_RIGHT;
if(buttons.pressed & DPAD_LEFT) direction = MOVE_LEFT;
}
if(direction.y == 0) {
// If we're not already moving along the Y axis,
// allow a change in direction along Y
if(buttons.pressed & DPAD_DOWN) direction = MOVE_DOWN;
if(buttons.pressed & DPAD_UP) direction = MOVE_UP;
}
// The last actual move made is remembered in last_move.
// You can go in any direction except the opposite of it.
if(buttons.pressed & DPAD_RIGHT && last_move != Left) direction = Right;
if(buttons.pressed & DPAD_LEFT && last_move != Right) direction = Left;
if(buttons.pressed & DPAD_DOWN && last_move != Up) direction = Down;
if(buttons.pressed & DPAD_UP && last_move != Down) direction = Up;
}