slowLineTo.cpp

#include <windows.h>
#include <tchar.h>

void FatalError(LPCTSTR errorMessage)
{
    MessageBox(NULL, errorMessage, _T("Fatal error"), MB_OK | MB_ICONERROR);
    exit(-1);
}

void Paint(HWND hWnd)
{
    const DWORD penStyle = PS_GEOMETRIC | PS_DOT | PS_JOIN_ROUND | PS_ENDCAP_ROUND;
    const DWORD penWidth = 1;

    PAINTSTRUCT ps;
    HDC         dc;
    HPEN        pen;
    LOGBRUSH    logBrush{0};
    RECT        clipRect;

    logBrush.lbColor = RGB(0, 0, 0);
    logBrush.lbStyle = BS_SOLID;
    logBrush.lbHatch = 0;

    pen = ExtCreatePen(penStyle, penWidth, &logBrush, 0, NULL);
    if ( !pen )
        FatalError(_T("Could not create the pen."));

    dc = BeginPaint(hWnd, &ps);
    GetClipBox(dc, &clipRect);

    if ( SelectObject(dc, pen) == HGDI_ERROR )
        FatalError(_T("Could not select the pen."));

    const int lineLength = 150000;
    const int x = 20;
    const int y = 20;
    const int yGap = 50;
    const int numLines = 2;

    for ( int i = 0; i < numLines; ++i )
    {
        MoveToEx(dc, x, y + (i * yGap), NULL);
        LineTo(dc, x + lineLength, y + (i * yGap));
    }

    EndPaint(hWnd, &ps);
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch ( message )
    {
        case WM_PAINT:
            Paint(hWnd);
            break;

        case WM_DESTROY:
            PostQuitMessage(0);
            break;

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

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, LPSTR, int nCmdShow)
{
    // create the app window

    LPCTSTR className = _T("SampleFrame");

    WNDCLASSEX wcex{0};

    wcex.cbSize         = sizeof(WNDCLASSEX);
    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.hInstance      = hInstance;
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszClassName  = className;

    if ( !RegisterClassEx(&wcex) )
        FatalError(_T("Could not register the class for the application window."));

    HWND hFrame = CreateWindow(className, _T("Sample Frame"), WS_OVERLAPPEDWINDOW,
                    CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);
    if ( !hFrame )
      FatalError(_T("Could not create the application window."));

    ShowWindow(hFrame, nCmdShow);
    UpdateWindow(hFrame);

    // run the message pump

    MSG msg;

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

    return (int)msg.wParam;
}