Win32版弹球程序

    弹球程序是个非常经典的程序，经常容易被问到或者考到，所以非常有必要掌握一下。其思想非常的简单，就是当碰到边缘的时候将所碰撞的边缘的方向上的速度变为反向，例如X方向上碰到了边缘，就将原来X方向上的速度变为负的，Y方向上的同理。然后就会产生一个全反射的碰撞反弹效果，Java下的弹球程序通过AWT或者Swing的低级绘图比较容易实现，个人觉得Win32下的实现更有意思，所以这里我们探索一下Win32下的实现，程序中已经包含了大量的注释，就不作过多解释了，直接上代码，本例在VC6下编译运行通过。

#include<windows.h>
#include<time.h>
/*
Win32版弹球程序
*/
//小球半径
#define RADIUS 50

//窗口类名称
char * className = "main";
//程序标题
char * appName = "弹球";

struct SBall
{
	int posX;
	int posY;
	
	int velX;
	int velY;
	
};
//取x-y范围的随机整数
int	  RandInt(int x,int y) {return rand()%(y-x+1)+x;}

LRESULT CALLBACK WinProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
	WNDCLASSEX wnd;
	wnd.cbClsExtra = 0;
	wnd.cbSize = sizeof(WNDCLASSEX);
	wnd.cbWndExtra = 0;
	wnd.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
	wnd.hCursor = LoadCursor(NULL,IDC_ARROW);
	wnd.hIcon = LoadIcon(NULL,IDI_APPLICATION);
	wnd.hInstance = hInstance;
	wnd.style = CS_VREDRAW | CS_HREDRAW;
	wnd.lpfnWndProc = WinProc;
	wnd.lpszClassName = className;
	wnd.lpszMenuName = NULL;
	wnd.hIconSm = LoadIcon(NULL,IDI_APPLICATION);

	if(!RegisterClassEx(&wnd))
	{
		MessageBox(NULL,"注册窗口类失败","提示",0);
		return 0;
	}

	HWND hwnd = CreateWindowEx(NULL,className,appName,WS_OVERLAPPEDWINDOW,0,0,400,300,NULL,NULL,hInstance,NULL);

	ShowWindow(hwnd,nCmdShow);
	UpdateWindow(hwnd);

	MSG msg;

	while (GetMessage(&msg,NULL,0,0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);

		InvalidateRect(hwnd,NULL,TRUE);
	}

	UnregisterClass(className,wnd.hInstance);
	
	return msg.wParam;
}

LRESULT CALLBACK WinProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam)
{
	//创建画刷
	static HBRUSH redBrush = CreateSolidBrush(RGB(255,0,0));
	static HBRUSH oldBrush = NULL;

	//创建一个小球
	static SBall *ball = new SBall();

	//客户区大小
	static int xClient,yClient;

	switch(msg)
	{
	case WM_CREATE:
		//获取客户区大小
		RECT rect;
		GetClientRect(hwnd,&rect);
		xClient = rect.right;
		yClient = rect.bottom;
		
		//初始化随机数生成器
		srand((unsigned)time(NULL));
		//初始化小球位置
		ball->posX = RandInt(0,xClient);
		ball->posY = RandInt(0,yClient);
		//初始化小球运动速度
		ball->velX = 10;
		ball->velY = 10;
		
		break;
	case WM_SIZE:
		//窗口大小发生变化，重新获取客户区大小
		xClient = LOWORD(lParam);
		yClient = HIWORD(lParam);
		break;
	case WM_PAINT:
		PAINTSTRUCT ps;
		BeginPaint(hwnd,&ps);

		//判断小球是否需要变换方向
		if (ball->posX+RADIUS >= xClient || ball->posX-RADIUS < 0)
		{
			ball->velX = -ball->velX;
		}
		if (ball->posY+RADIUS >= yClient || ball->posY-RADIUS < 0)
		{
			ball->velY = -ball->velY;
		}
		//小球按照当前速度移动一个单位
		ball->posX += ball->velX;
		ball->posY += ball->velY;

		//启用红色画刷
		oldBrush = (HBRUSH)SelectObject(ps.hdc,redBrush);
		//画出小球
		Ellipse(ps.hdc,ball->posX-RADIUS,ball->posY-RADIUS,ball->posX+RADIUS,ball->posY+RADIUS);
		//替换回老画刷
		SelectObject(ps.hdc,oldBrush);

		EndPaint(hwnd,&ps);
		Sleep(100);
		break;
	case WM_DESTROY:
		//退出程序前先清理内存占用
		DeleteObject(redBrush);
		DeleteObject(oldBrush);
		delete ball;
		
		PostQuitMessage (0);
		break;
	}
	return DefWindowProc(hwnd,msg,wParam,lParam);
}