GDI显示图像时设定窗口大小为图像大小

先前已经能基于GDI显示png图像，但是窗口大小和图像尺寸并不一致。注意到opencv中的imshow的窗口和图像尺寸一致，这里进行设置。

原理

CreateWindow阶段并不能确定窗口大小，但是在窗口处理函数的绘制阶段可以重新调整窗口大小。具体步骤按先后顺序：

• 首先读取图像（而不是像之前的博客中缩写的，每次窗口paint时都重新读取图像）

• 注册窗口

• CreateWindowEx时候随便设置一个窗口大小

• case WM_PAINT:阶段判断一下，如果没有调整过窗口大小，就调整

代码

#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;            //文件打开错误则返回 FILE_ERROR
	png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);        //创建png读取结构
	info_ptr = png_create_info_struct(png_ptr);        //png 文件信息结构
	png_init_io(png_ptr, fp);                //初始化文件 I\O
	png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0);                //读取png文件
	*pnWidth = png_get_image_width(png_ptr, info_ptr);        //获得图片宽度
	*pnHeight = png_get_image_height(png_ptr, info_ptr);        //获得图片高度
	color_type = png_get_color_type(png_ptr, info_ptr);        //获得图片色彩深度
	file_size = (*pnWidth) * (*pnHeight) * 4;                    //计算需要存储RGB(A)数据所需的内存大小
	*cbData = (unsigned char *)malloc(file_size);            //申请所需的内容, 并将 *cbData 指向申请的这块内容
	row_point = png_get_rows(png_ptr, info_ptr);            //读取RGB(A)数据
	block_size = color_type == 6 ? 4 : 3;                    //根据是否具有a通道判断每次所要读取的数据大小, 具有Alpha通道的每次读4位, 否则读3位
	//将读取到的RGB(A)数据按规定格式读到申请的内存中
	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
		//原样拷贝，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);//获得客户区的大小
		int nWidth = rcClient.right - rcClient.left;//客户区的宽度
		int nHeight = rcClient.bottom - rcClient.top;//客户区的高度
		StretchBlt(hdc, 0, 0, nWidth, nHeight, hdcMem, 0, 0, bm.bmWidth, bm.bmHeight, SRCCOPY);//拉伸拷贝
#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;
}

参考

设置窗口客户区大小的一种办法