HGE tutorial06

bool FrameFunc()
{
	float dt = hge->Timer_GetDelta();
	static float t = 0.0f;
	float tx, ty;
	int id;
	static int lastid = 0;

	// If ESCAPE was pressed, tell the GUI to finish
	if (hge->Input_GetKeyState(HGEK_ESCAPE)) { lastid = 5; gui->Leave(); }

	// We update the GUI and take an action if
	// one of the menu items was selected
	id = gui->Update(dt);
	if (id == -1)
	{
		switch (lastid)
		{
		case 1:
		case 2:
		case 3:
		case 4:
			gui->SetFocus(1);
			gui->Enter();
			break;

		case 5: return true;
		}
	}
	else if (id) { lastid = id; gui->Leave(); }

	// Here we update our background animation
	t += dt;
	tx = 50 * cosf(t / 60);
	ty = 50 * sinf(t / 60);

	quad.v[0].tx = tx;        quad.v[0].ty = ty;
	quad.v[1].tx = tx + 800 / 64; quad.v[1].ty = ty;
	quad.v[2].tx = tx + 800 / 64; quad.v[2].ty = ty + 600 / 64;
	quad.v[3].tx = tx;        quad.v[3].ty = ty + 600 / 64;

	return false;
}

在这个代码中，当gui->update(dt)之后，会进行动画的操作。关于gui->update(dt):

If one of the controls has changed it's state, Update returns that control's identificator. If leave method was called and all the controls have finished their animation, Update returns -1. Otherwise it returns 0.

按照这个解释，我们会遇到三种情况：

1）、指向了某个选项，但是没有选择，那么 return  0;

2）、指向并选择了某个选项，那么 return id; 之后会调用leave();然后选项会消失在屏幕上

3）、在2）之后的情况，调用leave()之后会立刻的 return -1。那么在return -1则会默认指向某个选项，并且会刷新使得选项出现。

将原来的if-else if改成了if-else if-else输出了当前指示的选项。