基于GDI显示png图像
intro
先前基于GDI已经能够显示BITMAP图像：windows下控制台程序实现窗口显示 ，其中BMP图像是使用LoadImage()这一Win32 API函数来做的。考虑到LoadImage()函数并不能读取png图像，因此需要libpng或stb等png编解码库的帮助。
网上找到相关代码不多，稍加修改可以运行，具备特点：
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纯C，单个文件（依赖的libpng和zlib可以忽略）
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直接读取png图像而不是通过读取.rc文件（资源文件）再读取png图像
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png图像的读取：基于libpng（以及zlib），我直接用的opencv345 windows预编译报里的.h文件和库文件
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入口函数为
main()而非WinMain()，也即控制台程序，方便作为库函数、移植 -
不同于BMP的地方：在窗口处理函数的创建阶段有所不同：
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); } -
并没有处理alpha通道
如果图像有alpha通道，透明区域将显示为黑色，因为用的是BitBlt()。如果要使用alpha通道（例如做融合，或者显示为黑色以外的颜色），则应当使用AlphaBlend()和msing32库：#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中看起来也是把透明区域显示为黑色。
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缺点：窗口client区域大小固定，没有能根据图像尺寸来变化
代码
#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;
}
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
//原样拷贝，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);//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)
{
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;
}
参考
使用 Libpng 配合 GDI 完成对 png 图片的解析与显示 ， 讲解细致
How would I load a PNG image using Win32/GDI (no GDI+ if possible)? (没用）
使用libpng和GDI读取显示png图片 (代码无法运行)
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