Merging two Gdiplus::Bitmap into one c++ - c++

Question

I have two bitmaps:
Gdiplus::Bitmap *pbmBitmap, pbmBitmap1;
They contains two images. How i can merge them into one image?
I was trying something like that:
Bitmap* dstBitmap = new Bitmap(pbmBitmap->GetWidth(), pbmBitmap->GetHeight() + pbmBitmap1->GetHeight()); //create dst bitmap
HDC dcmem = CreateCompatibleDC(NULL);
SelectObject(dcmem, pbmBitmap); //select first bitmap
HDC dcmemDst = CreateCompatibleDC(NULL);
SelectObject(dcmem1, dstBitmap ); //select destination bitmap
BitBlt(dcmemDst em1, 0, 0, pbmBitmap->GetWidth(), pbmBitmap->GetHeight(), dcmem, 0, 0, SRCCOPY); //copy first bitmap into destination bitmap
HBITMAP CreatedBitmap = CreateCompatibleBitmap(dcmem, pbmBitmap->GetWidth(), pbmBitmap->GetHeight() + pbmBitmap1->GetHeight());
dstBitmap = new Bitmap(CreatedBitmap, NULL);
dstBitmap ->Save(L"omg.bmp", &pngClsid, 0); //pngClsid i took from msdn
I know - ugly code, but i need to do it in C++.
I'm getting black image. Why?
//EDIT
After two hours googling and reading i got this:
HBITMAP bitmapSource;
pbmBitmap->GetHBITMAP(Color::White, &bitmapSource); //create HBITMAP from Gdiplus::Bitmap
HDC dcDestination = CreateCompatibleDC(NULL); //create device contex for our destination bitmap
HBITMAP HBitmapDestination = CreateCompatibleBitmap(dcDestination, pbmBitmap->GetWidth(), pbmBitmap->GetHeight()); //create HBITMAP with correct size
SelectObject(dcDestination, dcDestination); //select created hbitmap on our destination dc
HDC dcSource = CreateCompatibleDC(NULL); //create device contex for our source bitmap
SelectObject(dcSource, bitmapSource); //select source bitmap on our source dc
BitBlt(dcDestination, 0, 0, pbmBitmap->GetWidth(), pbmBitmap->GetHeight(), dcSource, 0, 0, SRCCOPY); //copy piece of bitmap with correct size
SaveBitmap(dcDestination, HBitmapDestination, "OMG.bmp"); //not working i get 24kb bitmap
//SaveBitmap(dcSource, bitmapSource, "OMG.bmp"); //works like a boss, so it's problem with SaveBitmap function
It should work, but i get 24kb bitmap.
SaveBitmap is my custom function, it works when i try save source bitmap.
Why i can't copy one bitmap to another??

Answer 1

Use a Graphics object to combine them. Here's some sample working code... Of course, you should use smart ptrs like unique_ptr<> instead of new/delete but I did not want to assume you're using VS 2012 or newer.
void CombineImages()
{
Status rc;
CLSID pngClsid;
GetEncoderClsid(L"image/png", &pngClsid);
Bitmap* bmpSrc1 = Bitmap::FromFile(L"Image1.JPG");
assert(bmpSrc1->GetLastStatus() == Ok);
Bitmap* bmpSrc2 = Bitmap::FromFile(L"Image2.JPG");
assert(bmpSrc2->GetLastStatus() == Ok);
Bitmap dstBitmap(bmpSrc1->GetWidth(), bmpSrc1->GetHeight() + bmpSrc2->GetHeight());
assert(dstBitmap.GetLastStatus() == Ok);
Graphics* g = Graphics::FromImage(&dstBitmap);
rc = g->DrawImage(bmpSrc1, 0, 0 );
assert(rc == Ok);
rc = g->DrawImage(bmpSrc2, 0, bmpSrc1->GetHeight());
assert(rc == Ok);
rc = dstBitmap.Save(L"Output.png", &pngClsid, NULL);
assert(rc == Ok);
delete g;
delete bmpSrc1;
delete bmpSrc2;
}
main fn..
int _tmain(int argc, _TCHAR* argv[])
{
ULONG_PTR token;
GdiplusStartupInput input;
GdiplusStartup(&token, &input, nullptr);
CombineImages();
GdiplusShutdown(token);
return 0;
}

Answer 2

Here is my own function that receives a vector of image files and merge them vercially.
wstring CombineBitmaps(vector files)
{
wstring NewFile{ L"Output.png" };
Gdiplus::Status rc;
CLSID pngClsid;
GetEncoderClsid(L"image/png", &pngClsid);
vector< Gdiplus::Bitmap*> bmpSrc;
int Height{ 0 };
for (int i = 0; i < files.size(); i++)
{
bmpSrc.push_back (Gdiplus::Bitmap::FromFile(files[i].c_str()));
Height += bmpSrc[0]->GetHeight();
}
Gdiplus::Bitmap dstBitmap(bmpSrc[0]->GetWidth(), Height);
Gdiplus::Graphics* g = Gdiplus::Graphics::FromImage(&dstBitmap);
for (int i = 0; i < files.size(); i++)
{
rc = g->DrawImage(bmpSrc[i], 0, i*bmpSrc[i]->GetHeight());
}
rc = dstBitmap.Save(NewFile.c_str(), &pngClsid, NULL);
delete g;
return NewFile;
}
You would call it as shown below:
vector<wstring> screens;
screens.push_back(L"screenshot1");
screens.push_back(L"screenshot2");
screens.push_back(L"screenshot3");
screens.push_back(L"screenshot4");
screens.push_back(L"screenshot5");
CombineBitmaps(screens);