GDI+ 图片转存

摘自MSDN,其中 GetEncoderClsid 第一个参数可为

L"image/bmp"
L"image/jpeg"
L"image/gif"
L"image/tiff"
L"image/png"

#include <windows.h>
#include <gdiplus.h>
#include <stdio.h>
using namespace Gdiplus;

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid);

int main() {
   // Initialize GDI+.
   GdiplusStartupInput gdiplusStartupInput;
   ULONG_PTR gdiplusToken;
   GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

   CLSID  encoderClsid;
   int    result;
   WCHAR  strGuid[39];

   result = GetEncoderClsid(L"image/png", &encoderClsid);

   if(result < 0) {
      printf("The PNG encoder is not installed.
");
   } else {
      Bitmap bmp(L"logo.bmp");
      bmp.Save(L"logo.png", &encoderClsid, NULL);
   }

   GdiplusShutdown(gdiplusToken);
   return 0;
}

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid) {
   UINT  num = 0;          // number of image encoders
   UINT  size = 0;         // size of the image encoder array in bytes

   ImageCodecInfo* pImageCodecInfo = NULL;

   GetImageEncodersSize(&num, &size);
   if(size == 0) {
      return -1;  // Failure
   }
   pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
   if(pImageCodecInfo == NULL) {
      return -1;  // Failure
   }

   GetImageEncoders(num, size, pImageCodecInfo);

   for(UINT j = 0; j < num; ++j) {
      if(wcscmp(pImageCodecInfo[j].MimeType, format) == 0) {
         *pClsid = pImageCodecInfo[j].Clsid;
         free(pImageCodecInfo);
         return j;  // Success
      }    
   }

   free(pImageCodecInfo);
   return -1;  // Failure
}