如何在不基于网格的蛇游戏（使用c ++和OpenGL）中实现食物生成器？

Question

The snake in my game is basically a list of squares. Each square in this list is defined using GL_QUADS, which requires definition of two vertices (x,y and x1,y1) as so:

void Square::draw() const
{
glBegin(GL_QUADS);

    glVertex2f(x, y);
    glVertex2f(x1, y);
    glVertex2f(x1, y1);
    glVertex2f(x, y1);

    glEnd();
}

The snake moves by insertion of a new element at the front of the list, and deletion of the last. So, if the snake was initially moving towards the left, and receives a command to move upwards, a square would be created above the snake's (previous) head, and the last square in the list will be removed.

To generate food, I have the following code:

void generate_food()
{
    time_t seconds
    time(&seconds);
    srand((unsigned int)seconds);

        x = (rand() % (max_width - min_width + 1)) + min_width;
        y = (rand() % (max_height - min_height + 1)) + min_height;
        x1 = foodx + 10;
        y1 = foody + 10;

    food = new Square{x,y,x1,y1 };
}

(Note: the width and height are dimensions of the playfield.)

I also implemented a function that grows the snake: if the coordinates of the snake's head match the coordinates of the food. However, when I run the program, the snake's head is never EXACTLY at the same coordinates as the food block... a few pixels off, here and there. Is there any way around this problem which does not require me to re-write all my code with a grid-based implementation?

Answer 1

As i understand your explanation when snake is moving you compare two squares: square of new head and food. So to get it work correctly you should detect collisions of squares and not full equality.

bool rectHitTest(const Square head, const Square food){
    if ((head.x2 < food.x1 || head.y2 < food.y1) || 
        (head.x1 > food.x2 || head.y1 > food.y2))
        return false;
    return true;
}

To allow it eat without graphical collision on the screen you can draw your food with base coords but test on collision with expanded for a few pixels