The Win95/Win98 Caret Bug

Listing 1: caretbug.c — Code to demonstrate caret bug

// caretbug.c -- program demonstrating SetCaretPos() problems

#define WIN32_LEAN_AND_MEAN
#include <windows.h>

#define TEST_CLASS      "CaretTest"

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam,
                        LPARAM lParam);
void OnKeyDown(HWND hwnd, UINT vk, int *x, int *y);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASS    wndClass;
    MSG         msg;
    HWND        hwnd;

    (void)UNREFERENCED_PARAMETER(hPrevInstance);
    (void)UNREFERENCED_PARAMETER(lpCmdLine);
    (void)UNREFERENCED_PARAMETER(nCmdShow);

    ZeroMemory(&wndClass, sizeof(WNDCLASS));
    wndClass.lpfnWndProc    = WndProc;
    wndClass.hInstance      = hInstance;
    wndClass.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wndClass.hbrBackground  = (HBRUSH) (COLOR_WINDOW + 1);
    wndClass.lpszClassName  = TEST_CLASS;

    if (!RegisterClass(&wndClass))
        return(FALSE);

    hwnd = CreateWindow(TEST_CLASS, "Caret Bug Demo",
                    WS_POPUPWINDOW | WS_CAPTION, 10, 10, 300, 300,
                    GetDesktopWindow(), NULL, hInstance, NULL);
    if (hwnd != NULL) {
        ShowWindow(hwnd, SW_SHOWNORMAL);
        UpdateWindow(hwnd);

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

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    static int      x, y;
    PAINTSTRUCT     ps;

    switch(uMsg) {
        case WM_CREATE:
            x = 10;
            y = 10;
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            break;
        case WM_PAINT:
            BeginPaint(hwnd, &ps);
            EndPaint(hwnd, &ps);
            return(0);
        case WM_SETFOCUS:
            CreateCaret(hwnd, NULL, 2, 20);
            SetCaretPos(x, y);
            ShowCaret(hwnd);
            break;
        case WM_KILLFOCUS:
            DestroyCaret();
            break;
        case WM_KEYDOWN:
            OnKeyDown(hwnd, (UINT) wParam, &x, &y);
            break;
    }
    return(DefWindowProc(hwnd, uMsg, wParam, lParam));
}

void OnKeyDown(HWND hwnd, UINT vk, int *x, int *y)
{
    RECT    r;
    BOOL    valid;

    valid = TRUE;
    switch(vk) {
        case VK_LEFT:
            *x -= 15;
            break;
        case VK_RIGHT:
            *x += 15;
            break;
        case VK_UP:
            *y -= 15;
            break;
        case VK_DOWN:
            *y += 15;
            break;
        default:
            valid = FALSE;
            break;
    }

    if (valid) {
        GetClientRect(hwnd, &r);
        if (*x < r.left)
            *x = r.left;
        if (*x >= r.right)
            *x = r.right - 1;
        if (*y < r.top)
            *y = r.top;
        if (*y >= r.bottom)
            *y = r.bottom - 1;

        r.bottom = 20;
        InvalidateRect(hwnd, &r, TRUE);

        SetCaretPos(*x, *y);
    }
}
//End of File