C++ Direct2D ID2D1HwndRenderTarget's parent IUnknown class' _vfptr variable becomes null - c++

Question

I have a Direct2D app that I am making, and I am writing a Direct2D library that makes using Direct2D easier for me as well. I'll post the exact problematic code if I need to, but my main issue is that I have an ID2D1HwndRenderTarget in the definition of one class, I extend that class with another class, in the child class I have a method that calls a method of the parent class that initializes the Render Target, and then in turn calls the load method of the child class. However, as soon as the program reaches the load content method of the child class, the __vfptr variable (I don't have a clue what that is) in the IUnknown portion of the ID2D1HwndRenderTarget is now null. The only reason I figured this out is in some other code I was getting an access violation error when using the render target to create a ID2D1Bitmap from an IWicBitmapSource. I don't understand how this happens because after initializing the Render Target, that _vfptr variable becomes null as soon as the method with the initialization code returns. Can anyone explain why this may be happening? My relevant code is below.
This code is called once to create the hwnd render target and the offscreen render target. This is in a dll project.
GameBase.cpp
HRESULT GameBase::Initialize(HINSTANCE hInst, HWND winHandle, struct DX2DInitOptions options)
{
this->mainRenderTarget = NULL;
this->offscreenRendTarget = NULL;
this->factory = NULL;
HRESULT result;
D2D1_FACTORY_OPTIONS factOptions;
D2D1_FACTORY_TYPE factType;
if(options.enableDebugging)
factOptions.debugLevel = D2D1_DEBUG_LEVEL::D2D1_DEBUG_LEVEL_ERROR;
else
factOptions.debugLevel = D2D1_DEBUG_LEVEL::D2D1_DEBUG_LEVEL_NONE;
if(options.singleThreadedApp)
factType = D2D1_FACTORY_TYPE_SINGLE_THREADED;
else
factType = D2D1_FACTORY_TYPE_MULTI_THREADED;
result = D2D1CreateFactory(factType, factOptions, &this->factory);
if(FAILED(result))
{
OutputDebugString(L"Failed to create a Direct 2D Factory!");
return result;
}
this->instance = hInst;
this->hwnd = winHandle;
D2D1_SIZE_U size = D2D1::SizeU(options.winWidth, options.winHeight);
this->width = options.winWidth;
this->height = options.winHeight;
result = factory->CreateHwndRenderTarget(D2D1::RenderTargetProperties(), D2D1::HwndRenderTargetProperties(winHandle, size), &this->mainRenderTarget);
if(FAILED(result))
{
OutputDebugString(L"Failed to create a render target to draw to the window with!");
return result;
}
result = this->mainRenderTarget->CreateCompatibleRenderTarget(&this->offscreenRendTarget);
if(FAILED(result))
{
OutputDebugString(L"Failed to create an offscreen render target from the main render target.");
return result;
}
return LoadContent();
}
After the call to LoadContent, at no point in time do I change the value of the mainRenderTarget.
DX2DImage.cpp
HRESULT DX2DImageLoader::LoadFromResource(LPCWSTR resourceName, LPCWSTR resourceType, HMODULE progModule, DX2DImage* image)
{
if(!this->isInit)
{
OutputDebugStringA("You must call InitializeImageLoader before using this image loader!");
return E_FAIL;
}
IWICBitmapDecoder *decoder = NULL;
IWICBitmapFrameDecode *source = NULL;
IWICStream *stream = NULL;
IWICFormatConverter *converter = NULL;
HRSRC imageResHandle = NULL;
HGLOBAL imageResDataHandle = NULL;
void *imageFile = NULL;
DWORD imageFileSize = 0;
HRESULT result;
//Find the image.
imageResHandle = FindResource(progModule, resourceName, resourceType);
if(!imageResHandle)
{
OutputDebugStringA("Failed to get a handle to the resource!");
return E_FAIL;
}
//Load the data handle of the image.
imageResDataHandle = LoadResource(progModule, imageResHandle);
if(!imageResDataHandle)
{
OutputDebugStringA("Failed to load the image from the module!");
return E_FAIL;
}
//Lock and retrieve the image.
imageFile = LockResource(imageResDataHandle);
if(!imageFile)
{
OutputDebugStringA("Failed to lock the image in the module!");
return E_FAIL;
}
//Get the size of the image.
imageFileSize = SizeofResource(progModule, imageResHandle);
if(!imageFileSize)
{
OutputDebugStringA("Failed to retrieve the size of the image in the module!");
return E_FAIL;
}
//Create a stream that will read the image data.
result = this->factory->CreateStream(&stream);
if(FAILED(result))
{
OutputDebugStringA("Failed to create an IWICStream!");
return result;
}
//Open a stream to the image.
result = stream->InitializeFromMemory(reinterpret_cast<BYTE*>(imageFile), imageFileSize);
if(FAILED(result))
{
OutputDebugStringA("Failed to initialize the stream!");
return result;
}
//Create a decoder from the stream
result = this->factory->CreateDecoderFromStream(stream, NULL, WICDecodeMetadataCacheOnDemand, &decoder);
if(FAILED(result))
{
OutputDebugStringA("Failed to create a decoder from the stream!");
return result;
}
//Get the first frame from the image.
result = decoder->GetFrame(0, &source);
if(FAILED(result))
{
OutputDebugStringA("Failed to get the first frame from the decoder!");
return result;
}
//Create a format converter to convert image to 32bppPBGRA
result = this->factory->CreateFormatConverter(&converter);
if(FAILED(result))
{
OutputDebugStringA("Failed to create a format converter!");
return result;
}
//Convert the image to the new format.
result = converter->Initialize(source, GUID_WICPixelFormat32bppPBGRA, WICBitmapDitherTypeNone, NULL, 0.0f, WICBitmapPaletteTypeMedianCut);
if(FAILED(result))
{
OutputDebugStringA("Failed to convert the image to the correct format!");
return result;
}
//Create the Direct2D Bitmap from the Wic Bitmap.
result = this->renderTarget->CreateBitmapFromWicBitmap(converter, NULL, &image->bitmap);
if(FAILED(result))
{
OutputDebugStringA("Failed to create a Direct 2D Bitmap from a WIC Bitmap!");
return result;
}
image->width = static_cast<UINT>(image->bitmap->GetSize().width);
image->height = static_cast<UINT>(image->bitmap->GetSize().height);
SafeRelease(&source);
SafeRelease(&converter);
SafeRelease(&decoder);
SafeRelease(&stream);
return S_OK;
}
The Access Violation exception occurs on the line
result = this->renderTarget->CreateBitmapFromWicBitmap(converter, NULL, &image->bitmap);
where image->bitmap is a currently NULL (Like it's supposed to be) ID2D1Bitmap.
Here, the renderTarget variable is the same mainRenderTarget variable from GameBase.cpp above. When I debug the line, all the parents of the RenderTarget are not null, however once I get to the IUnknown interface under it all, the _vfptr thing is null. This is not the case with the converter variable, this variable, or image variable.

Answer 1

I don't have enough code to debug your code, but from what I see I suspect the call to converter->Initialize(...) be invalid since MSDN say:
If you do not have a predefined palette, you must first create one. Use
InitializeFromBitmap to create the palette object, then pass it in along
with your other parameters.
dither, pIPalette, alphaThresholdPercent, and paletteTranslate are used to
mitigate color loss when converting to a reduced bit-depth format. For
conversions that do not need these settings, the following parameters values
should be used: dither set to WICBitmapDitherTypeNone, pIPalette set to NULL,
alphaThresholdPercent set to 0.0f, and paletteTranslate set to
WICBitmapPaletteTypeCustom.
And in your code you do not provide a valid pallete(you used NULL) and your paletteTranslate is not WICBitmapPaletteTypeCustom