我正在制作一个 Direct2D 应用程序，并且我正在编写一个 Direct2D 库，它也使我使用 Direct2D 更容易。如果需要，我将发布确切的有问题的代码，但我的主要问题是我在一个类的定义中有一个 ID2D1HwndRenderTarget，我用另一个类扩展了该类，在子类中我有一个调用方法的方法初始化Render Target的父类，然后依次调用子类的load方法。但是，一旦程序到达子类的加载内容方法，ID2D1HwndRenderTarget 的 IUnknown 部分中的 __vfptr 变量（我不知道那是什么）现在为空。我发现这一点的唯一原因是在其他一些代码中，当使用渲染目标从 IWicBitmapSource 创建 ID2D1Bitmap 时，我遇到了访问冲突错误。我不明白这是怎么发生的，因为在初始化渲染目标之后，只要带有初始化代码的方法返回，_vfptr 变量就会变为空。谁能解释为什么会发生这种情况？我的相关代码如下。
此代码被调用一次以创建 hwnd 渲染目标和离屏渲染目标。这是在一个 dll 项目中。游戏基础.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();
}
在调用 LoadContent 之后，我不会更改 mainRenderTarget 的值。
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;
}
线路发生Access Violation异常
result = this->renderTarget->CreateBitmapFromWicBitmap(converter, NULL, &image->bitmap);
其中 image->bitmap 是当前为 NULL（就像它应该是）ID2D1Bitmap。
这里，renderTarget 变量与上面 GameBase.cpp 中的 mainRenderTarget 变量相同。当我调试该行时，RenderTarget 的所有父级都不为空，但是一旦我到达它下面的 IUnknown 接口，_vfptr 的东西就是空的。对于转换器变量、此变量或图像变量，情况并非如此。