试图写一个 function 让精灵在 Allegro 中从左到右移动

Question

I'm still pretty new with C/C++, and this seems like it should be easy, but I simply want a ball to move from left to right on my screen, and I can't seem to get it working. Through trial and error, I can either get the bmp to load as a block of pixels (ie it's not loading, and it just keeps randomly restarting right on the left side of the screen), or it doesn't load at all.

I just think I broke my brain trying to figure everything out, cause I've done more complicated things but this should be sooo easy!

Here is my function to load the ball.bmp as a bitmap:

void setupballs()
{
    ball_bmp = load_bitmap("ball.bmp", NULL);
    
    balls[0] = &active_ball[0];
    balls[0]->x = 0;
    balls[0]->y = 0;
    balls[0]->width = ball_bmp->w;
    balls[0]->height = ball_bmp->h;
    
}

Here is my function to update the ball as it moves across the screen.

void updateballs(int num) 
{
    int x, y;

    balls[num]->x = SCREEN_W / 2;
    balls[num]->y = SCREEN_H / 2;

    if (!balls[num]->alive) return;

    //move bullet
    balls[num]->x = x + 22;
    balls[num]->y = y;
    balls[num]->xspeed = ballspeed;
    balls[num]->yspeed = 0;

    //stay within the screen
    if (x < 6 || x > SCREEN_W - 6 || y < 55 || y > SCREEN_H - 6)
    {
        balls[num]->alive = 0;
        return;
    }

    draw_sprite(screen, ball_bmp, x, y);
}

And the game loop in my main.c file

//game loop
    while (!gameover)
    {
        changeMusic();
        displayHelp();
        if (startScreenMode == 1)
        {

            loadBackgroundImage("title.bmp");
            
            if (key[KEY_F1]) 
            {
                startScreenMode = 0;
                gameMode = 1;
            }
        }
        // Else if in game mode, do game stuff.
        else if (gameMode == 1)
        {
            loadBackgroundImage("background.bmp");
            
            //update balls
            updateballs(0);

            //move the ships
            moveship(0);

            //draw the ship
            drawship(0);

            //update the bullet
            updatebullet(0);

            //check for keypresses
            if (keypressed())
                getinput();

            //slow the game down
            rest(20);
        }
        else if (gameMode == 2)
        {
            displayHelp();
        }
    }