c++ - sdl 45 度运动

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我试图让我的物体以 45 度对角线移动。当它达到屏幕宽度时，它应该弹起来，我在某个地方犯了一个大错误，但无法弄清楚。

distance = 0;
etiSpeed = 1;

t2 = SDL_GetTicks();
delta = (t2 - t1) * 0.001;
t1 = t2;

distance += etiSpeed * delta;



    ball_x = ball_x * distance * ball_x_vel;
    ball_y = ball_y  * distance * ball_y_vel;

    if (ball_x < SCREEN_WIDTH)
    {
        ball_x_vel = 1;
        DrawSurface(screen, ball, ball_x, ball_y);
    }

else if (ball_x = SCREEN_WIDTH)
    {
        ball_x_vel = -1;
       DrawSurface(screen, ball, ball_x, ball_y);       
    }

Answer 1

你的测试不正确

if (ball_x = SCREEN_WIDTH)

正在将ball_x位置设置为SCREEN_WIDTH，作为 bool 测试，该位置将为true，因此将执行下一个代码块。我认为您正在尝试测试

if (ball_x == SCREEN_WIDTH)

但这也是不正确的，应该是

if (ball_x >= SCREEN_WIDTH)

即使这仍然太简单，如果球在屏幕外，您需要重新定位球。

if (ball_x >= SCREEN_WIDTH)
    ball_x = (SCREEN_WIDTH - 1) - (ball_x -(SCREEN_WIDTH-1));

假设你有

#define SCREEN_WIDTH 40
...
ball_x = 40;
if (ball_x >= SCREEN_WIDTH)
    ball_x = (SCREEN_WIDTH - 1) - (ball_x -(SCREEN_WIDTH-1));

计算结果为 39 - (40-39) = 38，当球超出 1 时，反弹 1。