MOOC清华《VC++面向对象与可视化程序设计》第2章：编程作业-渐变图形的绘制（“万花筒”程序）

#include <windows.h>
#include <math.h>
LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInst,
				   LPSTR lpszCmdLine, int nCmdShow)
{
	HWND hwnd;
	MSG msg;
	WNDCLASS wndclass;
	char lpszClassName[]="万花筒";
	char lpszTitle[]="万花筒";
	wndclass.style=0;
	wndclass.lpfnWndProc=WndProc;
	wndclass.cbClsExtra=0;
	wndclass.cbWndExtra=0;
	wndclass.hInstance=hInstance;
	wndclass.hIcon=LoadIcon(NULL,IDI_APPLICATION);
	wndclass.hCursor=LoadCursor(NULL,IDC_ARROW);
	wndclass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
	wndclass.lpszMenuName=NULL;
	wndclass.lpszClassName=lpszClassName;
	if(! RegisterClass(&wndclass))
	{
		MessageBeep(0);
		return FALSE;
	}

	hwnd=CreateWindow
		(
		lpszClassName,
		lpszTitle,
		WS_OVERLAPPEDWINDOW,
		0,
		0,
		500,
		400,
		NULL,
		NULL,
		hInstance,
		NULL
		);

	ShowWindow(hwnd,nCmdShow);
	UpdateWindow(hwnd);
	while(GetMessage(&msg,NULL,0,0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}
	return msg.wParam;
}

HPEN hpen[6];
LRESULT CALLBACK WndProc( HWND hwnd,
						  UINT message, 
						  WPARAM wParam, 
						  LPARAM lParam
						 )
{
	HDC hdc;
	PAINTSTRUCT ps;
			
	switch(message)
	{
	case WM_CREATE:
		{
			hpen[0]=(HPEN)CreatePen(PS_SOLID,0,RGB(125,0,0));
			hpen[1]=(HPEN)CreatePen(PS_SOLID,0,RGB(255,0,0));
			hpen[2]=(HPEN)CreatePen(PS_SOLID,0,RGB(0,125,0));
			hpen[3]=(HPEN)CreatePen(PS_SOLID,0,RGB(0,255,0));
			hpen[4]=(HPEN)CreatePen(PS_SOLID,0,RGB(0,0,125));
			hpen[5]=(HPEN)CreatePen(PS_SOLID,0,RGB(0,0,255));
		}
		break;
	
	case WM_PAINT:
	{
		double t;
		int x0=220,y0=200;
		int n=25,i,j,r=150;
		int x[50],y[50];
		t=6.28318/n;

		hdc=BeginPaint(hwnd,&ps);
		
		for(i=0;i<n;i++)
		{
			x[i]=int(r*cos(i*t)+x0);
			y[i]=int(r*sin(i*t)+y0);
		}
		for(i=0;i<=n-2;i++)
		{
			for(j=i+1;j<=n-1;j++)
			{
				SelectObject(hdc,hpen[j%6]);
				Sleep(50);
				MoveToEx(hdc,x[i],y[i],NULL);
				LineTo(hdc,x[j],y[j]);
			}
		}

		EndPaint(hwnd,&ps);
	}
		break;

	case WM_DESTROY:
		PostQuitMessage(0);
		break;

	default:
		return DefWindowProc(hwnd,message,wParam,lParam);
	}
	return 0;
}