用WinAPI实现一个图片查看器：一个打开按钮，点击后打开一个打开文件对话框，打开选中的png文件显示在屏幕上，并可以用鼠标滚轮调整大小

你可以使用WinAPI来实现一个图片查看器。下面是一个简单的示例代码，它包含一个打开按钮，点击后会打开一个打开文件对话框，选中的png文件将显示在屏幕上，并且可以使用鼠标滚轮调整大小。

#include <Windows.h>

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    // 注册窗口类
    WNDCLASSEX wcex;
    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc = WndProc;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance;
    wcex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = "ImageViewer";
    wcex.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

    if (!RegisterClassEx(&wcex))
    {
        MessageBox(NULL, "窗口类注册失败！", "错误", MB_ICONERROR);
        return -1;
    }

    // 创建窗口
    HWND hWnd = CreateWindow("ImageViewer", "图片查看器", WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 800, 600, NULL, NULL, hInstance, NULL);

    if (!hWnd)
    {
        MessageBox(NULL, "窗口创建失败！", "错误", MB_ICONERROR);
        return -1;
    }

    // 显示窗口
    ShowWindow(hWnd, nCmdShow);
    UpdateWindow(hWnd);

    // 消息循环
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    static HBITMAP hBitmap = NULL;

    switch (msg)
    {
    case WM_CREATE:
    {
        // 创建打开按钮
        HWND hOpenButton = CreateWindow("BUTTON", "打开", WS_CHILD | WS_VISIBLE | BS_PUSHBUTTON,
            10, 10, 80, 30, hwnd, NULL, ((LPCREATESTRUCT)lParam)->hInstance, NULL);
        break;
    }
    case WM_COMMAND:
    {
        // 处理按钮点击事件
        if (lParam && LOWORD(wParam) == BN_CLICKED)
        {
            // 创建打开文件对话框
            OPENFILENAME ofn;
            char szFileName[MAX_PATH] = "";
            ZeroMemory(&ofn, sizeof(ofn));
            ofn.lStructSize = sizeof(ofn);
            ofn.hwndOwner = hwnd;
            ofn.lpstrFilter = "PNG 图片\0*.png\0";
            ofn.lpstrFile = szFileName;
            ofn.nMaxFile = sizeof(szFileName);
            ofn.Flags = OFN_EXPLORER | OFN_FILEMUSTEXIST | OFN_HIDEREADONLY;
            ofn.lpstrDefExt = "png";

            if (GetOpenFileName(&ofn))
            {
                // 加载选中的png图片
                hBitmap = (HBITMAP)LoadImage(NULL, ofn.lpstrFile, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);

                if (hBitmap)
                {
                    // 调整窗口大小与图片大小一致
                    BITMAP bm;
                    GetObject(hBitmap, sizeof(bm), &bm);
                    RECT rc;
                    GetClientRect(hwnd, &rc);
                    SetWindowPos(hwnd, NULL, 0, 0, bm.bmWidth, bm.bmHeight, SWP_NOMOVE | SWP_NOZORDER | SWP_FRAMECHANGED);

                    // 重绘窗口
                    InvalidateRect(hwnd, NULL, TRUE);
                }
                else
                {
                    MessageBox(hwnd, "无法加载图片！", "错误", MB_ICONERROR);
                }
            }
        }
        break;
    }
    case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        if (hBitmap)
        {
            // 绘制图片
            HDC hdcMem = CreateCompatibleDC(hdc);
            HBITMAP hOldBitmap = (HBITMAP)SelectObject(hdcMem, hBitmap);

            RECT rc;
            GetClientRect(hwnd, &rc);
            StretchBlt(hdc, 0, 0, rc.right, rc.bottom, hdcMem, 0, 0, ps.rcPaint.right, ps.rcPaint.bottom, SRCCOPY);

            SelectObject(hdcMem, hOldBitmap);
            DeleteDC(hdcMem);
        }

        EndPaint(hwnd, &ps);
        break;
    }
    case WM_MOUSEWHEEL:
    {
        // 处理鼠标滚轮事件
        if (hBitmap)
        {
            short zDelta = GET_WHEEL_DELTA_WPARAM(wParam);
            RECT rc;
            GetClientRect(hwnd, &rc);

            if (zDelta > 0)
            {
                // 放大
                rc.right += 10;
                rc.bottom += 10;
            }
            else
            {
                // 缩小
                rc.right -= 10;
                rc.bottom -= 10;
            }

            // 设置新的窗口大小
            SetWindowPos(hwnd, NULL, 0, 0, rc.right, rc.bottom, SWP_NOMOVE | SWP_NOZORDER | SWP_FRAMECHANGED);

            // 重绘窗口
            InvalidateRect(hwnd, NULL, TRUE);
        }
        break;
    }
    case WM_DESTROY:
    {
        // 释放资源
        if (hBitmap)
        {
            DeleteObject(hBitmap);
        }

        PostQuitMessage(0);
        break;
    }
    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
    }

    return 0;
}

这是一个简单的图片查看器示例，仅供参考。你可以根据自己的需求进行修改和扩展。