windows程序设计之编写应用程序，当按下鼠标左键并在窗口中移动时，窗口中鼠标所经历的个点颜色设置为黑色

//Windows3.cpp: 定义应用程序的入口点。
//

#include "stdafx.h"
#include "Windows3.h"

#define MAX_LOADSTRING 100
#define MAXPOINTS 1000

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
	PSTR szCmdLine, int iCmdShow)
{

	static TCHAR	szAppName[] = TEXT("Windows3");
	HWND			hwnd;
	MSG			msg;
	WNDCLASS		wndclass;

	wndclass.style = CS_HREDRAW | CS_VREDRAW;
	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 = szAppName;

	if (!RegisterClass(&wndclass))
	{
		MessageBox(NULL, TEXT("Windows3"),
			szAppName, MB_ICONERROR);
		return 0;
	}

	hwnd = CreateWindow(szAppName, TEXT("Windows3"),
		WS_OVERLAPPEDWINDOW,
		CW_USEDEFAULT, CW_USEDEFAULT,
		CW_USEDEFAULT, CW_USEDEFAULT,
		NULL, NULL, hInstance, NULL);

	ShowWindow(hwnd, iCmdShow);
	UpdateWindow(hwnd);

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

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	static POINT	point[MAXPOINTS];       
	static int		num;
	HDC			hdc;
	PAINTSTRUCT		ps;

	switch (message)
	{
	case WM_LBUTTONDOWN:
		num = 0;
		InvalidateRect(hwnd, NULL, TRUE);
		return 0;

	case WM_MOUSEMOVE:
		if (wParam & MK_LBUTTON && num < MAXPOINTS)
		{
			point[num].x = LOWORD(lParam);
			point[num].y = HIWORD(lParam);
			num++;
			hdc = GetDC(hwnd);
			SetPixel(hdc, LOWORD(lParam), HIWORD(lParam), 0);   //将经过的点的颜色改为黑色
			ReleaseDC(hwnd, hdc);
		}
		return 0;

	case WM_LBUTTONUP:
		InvalidateRect(hwnd, NULL, FALSE);
		return 0;

	case WM_PAINT:
		hdc = BeginPaint(hwnd, &ps);
		for (int i = 0; i < num - 1; i++)
			for (int j = i + 1; j < num; j++)
			{

				MoveToEx(hdc, point[i].x, point[i].y, NULL);
				LineTo(hdc, point[j].x, point[j].y);
			}

		EndPaint(hwnd, &ps);
		return 0;

	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	}
	return DefWindowProc(hwnd, message, wParam, lParam);
}