基於GDI顯示png圖像

intro

先前基於GDI已經可以顯示BITMAP圖像：windows下控制檯程序實現窗口顯示 ，其中BMP圖像是使用LoadImage()這一Win32 API函數來作的。考慮到LoadImage()函數並不能讀取png圖像，所以須要libpng或stb等png編解碼庫的幫助。

網上找到相關代碼很少，稍加修改能夠運行，具有特色：

• 純C，單個文件（依賴的libpng和zlib能夠忽略）

• 直接讀取png圖像而不是經過讀取.rc文件（資源文件）再讀取png圖像

• png圖像的讀取：基於libpng（以及zlib），我直接用的opencv345 windows預編譯報裏的.h文件和庫文件

• 入口函數爲main()而非WinMain()，也即控制檯程序，方便做爲庫函數、移植

• 不一樣於BMP的地方：在窗口處理函數的建立階段有所不一樣：
  C 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) { ReadPngData("D:/work/libfc/imgs/Lena.png", &im_width, &im_height, &my_window->imdata); my_window->hBmp = CreateBitmap(im_width, im_height, 32, 1, my_window->imdata); }

• 並無處理alpha通道
  若是圖像有alpha通道，透明區域將顯示爲黑色，由於用的是BitBlt()。若是要使用alpha通道（例如作融合，或者顯示爲黑色之外的顏色），則應當使用AlphaBlend()和msing32庫：
  ```C
  #pragma comment(lib, "msimg32.lib")
  ...

  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);

  ```
  opencv中看起來也是把透明區域顯示爲黑色。

• 缺點：窗口client區域大小固定，沒有能根據圖像尺寸來變化

代碼

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


#define CRTDBG_MAP_ALLOC 
#include <crtdbg.h>


#pragma comment(lib, "D:/work/libfc/lib/libpng.lib")
#pragma comment(lib, "D:/work/libfc/lib/zlib.lib")

typedef struct MyRect {
    int x, y, width, height;
} MyRect;

const char* project_root = "D:/work/libfc";
char bitmap_im_pth[100];

typedef struct MyWindow {
    HDC dc;
    //HGDIOBJ image;
    HBITMAP hBmp;
    unsigned char* imdata;
} 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;
}


LRESULT __stdcall WindowProcedure(HWND window, unsigned int msg, WPARAM wp, LPARAM lp)
{
    int im_width, im_height;
    
    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) {
            ReadPngData("D:/work/libfc/imgs/Lena.png", &im_width, &im_height, &my_window->imdata);
            my_window->hBmp = CreateBitmap(im_width, 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:
    {
        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);
#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)
{
    MyRect rect;
    rect.x = 300;
    rect.y = 300;
    rect.width = 640;
    rect.height = 480;

    DWORD defStyle = WS_VISIBLE | WS_MINIMIZEBOX | WS_MAXIMIZEBOX | WS_SYSMENU;

    HWND hwnd = CreateWindowEx(0, szWindowClass, "title",
        defStyle, rect.x, rect.y,
        rect.width, rect.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 = my_window; // write back
}

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

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

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

    MyRegisterClass(hInstance);
    create_my_window(&my_window);

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

    destroy_my_window(my_window);


    return 0;
    
}

參考

使用 Libpng 配合 GDI 完成對 png 圖片的解析與顯示 ， 講解細緻

How would I load a PNG image using Win32/GDI (no GDI+ if possible)? (沒用）

使用libpng和GDI讀取顯示png圖片 (代碼沒法運行)