GDI顯示圖像時設定窗口大小爲圖像大小

先前已經能基於GDI顯示png圖像，可是窗口大小和圖像尺寸並不一致。注意到opencv中的imshow的窗口和圖像尺寸一致，這裏進行設置。

原理

CreateWindow階段並不能肯定窗口大小，可是在窗口處理函數的繪製階段能夠從新調整窗口大小。具體步驟按前後順序：

• 首先讀取圖像（而不是像以前的博客中縮寫的，每次窗口paint時都從新讀取圖像）

• 註冊窗口

• CreateWindowEx時候隨便設置一個窗口大小

• case WM_PAINT:階段判斷一下，若是沒有調整過窗口大小，就調整

代碼

#include <stdio.h>
#include <stdbool.h>
#include <windows.h>
#include "png.h"

#pragma comment(lib, "D:/work/libfc/lib/libpng.lib")
#pragma comment(lib, "D:/work/libfc/lib/zlib.lib")
//#pragma comment(lib, "msimg32.lib") // for png's alpha channel

typedef struct MyWindow {
    HDC dc;
    //HGDIOBJ image;
    HBITMAP hBmp;
    unsigned char* imdata;
    int im_width;
    int im_height;
    int win_pos_x; // window position, top left point's x coordinate
    int win_pos_y; // window posttion, top left point's y coordinate
    bool adjusted;
} MyWindow;

MyWindow* my_window;
enum ImageType {BMP, PNG};

long ReadPngData(const char *szPath, int *pnWidth, int *pnHeight, unsigned char **cbData)
{
    FILE *fp = NULL;
    long file_size = 0, pos = 0, mPos = 0;
    int color_type = 0, x = 0, y = 0, block_size = 0;

    png_infop info_ptr;
    png_structp png_ptr;
    png_bytep *row_point = NULL;

    fp = fopen(szPath, "rb");
    if (!fp)    return -1;            //文件打開錯誤則返回 FILE_ERROR

    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);        //建立png讀取結構
    info_ptr = png_create_info_struct(png_ptr);        //png 文件信息結構
    png_init_io(png_ptr, fp);                //初始化文件 I\O
    png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0);                //讀取png文件

    *pnWidth = png_get_image_width(png_ptr, info_ptr);        //得到圖片寬度
    *pnHeight = png_get_image_height(png_ptr, info_ptr);        //得到圖片高度
    color_type = png_get_color_type(png_ptr, info_ptr);        //得到圖片色彩深度
    file_size = (*pnWidth) * (*pnHeight) * 4;                    //計算須要存儲RGB(A)數據所需的內存大小
    *cbData = (unsigned char *)malloc(file_size);            //申請所需的內容, 並將 *cbData 指向申請的這塊內容

    row_point = png_get_rows(png_ptr, info_ptr);            //讀取RGB(A)數據

    block_size = color_type == 6 ? 4 : 3;                    //根據是否具備a通道判斷每次所要讀取的數據大小, 具備Alpha通道的每次讀4位, 不然讀3位

    //將讀取到的RGB(A)數據按規定格式讀到申請的內存中
    for (x = 0; x < *pnHeight; x++)
        for (y = 0; y < *pnWidth*block_size; y += block_size)
        {
            (*cbData)[pos++] = row_point[x][y + 2];        //B
            (*cbData)[pos++] = row_point[x][y + 1];        //G
            (*cbData)[pos++] = row_point[x][y + 0];        //R
            (*cbData)[pos++] = row_point[x][y + 3];        //alpha
        }

    png_destroy_read_struct(&png_ptr, &info_ptr, 0);
    fclose(fp);

    return file_size;
}


//int DEFAULT_WIDTH, DEFAULT_HIGHT;
void SetWindowSize(HWND hWnd)
{
    if (my_window->adjusted == false) {
        RECT WindowRect;
        RECT ClientRect;
        GetWindowRect(hWnd, &WindowRect);
        GetClientRect(hWnd, &ClientRect);
        WindowRect.right += (my_window->im_width - ClientRect.right);
        WindowRect.bottom += (my_window->im_height - ClientRect.bottom);
        MoveWindow(hWnd, WindowRect.left, WindowRect.top, WindowRect.right - WindowRect.left, WindowRect.bottom - WindowRect.top, true);
    }

    my_window->adjusted = true;
}


LRESULT __stdcall WindowProcedure(HWND window, unsigned int msg, WPARAM wp, LPARAM lp)
{
    int image_type = PNG;
    switch (msg)
    {
    case WM_CREATE:
        if (image_type == BMP) {
            my_window->hBmp = (HBITMAP)LoadImage(NULL, "D:/work/libfc/imgs/lena512.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
        }
        else if (image_type == PNG) {
            //
            my_window->hBmp = CreateBitmap(my_window->im_width, my_window->im_height, 32, 1, my_window->imdata);
        }
        if (my_window->hBmp == NULL)
            MessageBox(window, "Could not load image!", "Error", MB_OK | MB_ICONEXCLAMATION);
        break;

    case WM_PAINT:
    {
        SetWindowSize(window);
        BITMAP bm;
        PAINTSTRUCT ps;

        HDC hdc = BeginPaint(window, &ps);
        SetStretchBltMode(hdc, COLORONCOLOR);

        my_window->dc = CreateCompatibleDC(hdc);
        HBITMAP hbmOld = SelectObject(my_window->dc, my_window->hBmp);

        GetObject(my_window->hBmp, sizeof(bm), &bm);

#if 1
        //原樣拷貝，不支持拉伸
        BitBlt(hdc, 0, 0, bm.bmWidth, bm.bmHeight, my_window->dc, 0, 0, SRCCOPY);
        //AlphaBlend(hdc, 100, 0, bm.bmWidth, bm.bmHeight, my_window->dc, 0, 0, bm.bmWidth, bm.bmHeight, bf);
#else
        RECT rcClient;
        GetClientRect(window, &rcClient);//得到客戶區的大小
        int nWidth = rcClient.right - rcClient.left;//客戶區的寬度
        int nHeight = rcClient.bottom - rcClient.top;//客戶區的高度
        StretchBlt(hdc, 0, 0, nWidth, nHeight, hdcMem, 0, 0, bm.bmWidth, bm.bmHeight, SRCCOPY);//拉伸拷貝
#endif

        SelectObject(my_window->dc, hbmOld);
        DeleteDC(my_window->dc);

        EndPaint(window, &ps);
    }
    break;

    case WM_DESTROY:
        printf("\ndestroying window\n");
        PostQuitMessage(0);
        return 0L;

    case WM_LBUTTONDOWN:
        printf("\nmouse left button down at (%d, %d)\n", LOWORD(lp), HIWORD(lp));

        // fall thru
    default:
        //printf(".");
        return DefWindowProc(window, msg, wp, lp);
    }
}

const char* szWindowClass = "myclass";


ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEX wc;
    wc.cbSize = sizeof(WNDCLASSEX);
    /* Win 3.x */
    wc.style = CS_DBLCLKS;
    wc.lpfnWndProc = WindowProcedure;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = GetModuleHandle(0);
    wc.hIcon = LoadIcon(0, IDI_APPLICATION);
    wc.hCursor = LoadCursor(0, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszMenuName = 0;
    wc.lpszClassName = szWindowClass;
    /* Win 4.0 */
    wc.hIconSm = LoadIcon(0, IDI_APPLICATION);

    return RegisterClassEx(&wc);
}

BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
    my_window->win_pos_x = 600;
    my_window->win_pos_y = 300;

    DWORD defStyle = WS_VISIBLE | WS_MINIMIZEBOX | WS_MAXIMIZEBOX | WS_SYSMENU;

    HWND hwnd = CreateWindowEx(0, szWindowClass, "title",
        defStyle, my_window->win_pos_x, my_window->win_pos_y,
        my_window->im_width, my_window->im_height, 0, 0, hInstance, 0);

    if (!hwnd)
    {
        return FALSE;
    }
    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    return TRUE;
}

void create_my_window(MyWindow** _my_window) {
    MyWindow* my_window = (MyWindow*)malloc(sizeof(MyWindow));
    my_window->dc = NULL;
    my_window->imdata = NULL;
    my_window->hBmp = NULL;

    my_window->adjusted = false;

    *_my_window = my_window; // write back
}

void destroy_my_window(MyWindow* my_window) {
    if (my_window) {
        free(my_window);
    }
}

int main()
{
    printf("hello world!\n");
    
    create_my_window(&my_window);

    int im_width, im_height;
    unsigned char* imdata;
    ReadPngData("D:/work/libfc/imgs/op.png", &im_width, &im_height, &imdata);
    my_window->im_width = im_width;
    my_window->im_height = im_height;
    my_window->imdata = imdata;

    HINSTANCE hInstance = GetModuleHandle(0);
    int nCmdShow = SW_SHOWDEFAULT;

    MyRegisterClass(hInstance);

    if (!InitInstance(hInstance, nCmdShow))
    {
        return FALSE;
    }
        
    MSG msg;
    while (GetMessage(&msg, 0, 0, 0)) {
        DispatchMessage(&msg);
    }

    destroy_my_window(my_window);
    free(imdata);


    return 0;
    
}

參考

設置窗口客戶區大小的一種辦法