Windows程序设计珍藏版-正弦波源码

WM_CREATE，WM_SIZE，WM_PAINT三个消息的先后顺序

/*-----------------------------------------
   SINEWAVE.C -- Sine Wave Using Polyline
                 (c) Charles Petzold, 1998
  -----------------------------------------*/

#include <windows.h>
#include <math.h>

#define NUM    1000
#define TWOPI  (2 * 3.14159)

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

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("SineWave");
    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("Program requires Windows NT!"),
            szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szAppName, TEXT("Sine Wave Using Polyline"),
        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 int  cxClient, cyClient;
    HDC         hdc;
    int         i;
    PAINTSTRUCT ps;
    POINT       apt[NUM];
    CREATESTRUCT cs;
    RECT cr;

    switch (message)
    {
      //源码中没有对这个消息的处理，自己添加，以及上边的cr变量;
    case WM_CREATE:
        GetClientRect(hwnd, &cr);
        cxClient = cr.right - cr.left;
        cyClient = cr.bottom - cr.top;
        return 0;
    case WM_SIZE:
        cxClient = LOWORD(lParam);
        cyClient = HIWORD(lParam);
        return 0;

    case WM_PAINT:
        hdc = BeginPaint(hwnd, &ps);

        MoveToEx(hdc, 0, cyClient / 2, NULL);
        LineTo(hdc, cxClient, cyClient / 2);
        
        for (i = 0; i < NUM; i++)
        {
            apt[i].x = i * cxClient / NUM;
            apt[i].y = (int)(cyClient / 2 * (1 - sin(TWOPI * i / NUM)));
        }

        Polyline(hdc, apt, NUM);
        
        EndPaint(hwnd, &ps);
        return 0;

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

在三个消息后边下断点，发现先后顺序是

WM_CREATE，WM_PAINT，WM_SIZE，

源码中没有对create消息进行处理，导致程序一开始运行时，先处理paint的消息时，cxClient和cyClient初始值都还是0，看不到曲线波图形。点击最大最小化按钮，触发WM_SIZE消息后，对cxClient和cyClient复制后，才看到曲线波。