windowscodecs: Do not assume that vtable is the first element of the object,…

dlls/windowscodecs/jpegformat.c

@@ -175,9 +175,10 @@ static HRESULT WINAPI JpegDecoder_QueryInterface(IWICBitmapDecoder *iface, REFII
 
     if (!ppv) return E_INVALIDARG;
 
-    if (IsEqualIID(&IID_IUnknown, iid) || IsEqualIID(&IID_IWICBitmapDecoder, iid))
+    if (IsEqualIID(&IID_IUnknown, iid) ||
+        IsEqualIID(&IID_IWICBitmapDecoder, iid))
     {
-        *ppv = This;
+        *ppv = &This->IWICBitmapDecoder_iface;
     }
     else
     {
@@ -469,6 +470,8 @@ static const IWICBitmapDecoderVtbl JpegDecoder_Vtbl = {
 static HRESULT WINAPI JpegDecoder_Frame_QueryInterface(IWICBitmapFrameDecode *iface, REFIID iid,
     void **ppv)
 {
+    JpegDecoder *This = impl_from_IWICBitmapFrameDecode(iface);
+
     TRACE("(%p,%s,%p)\n", iface, debugstr_guid(iid), ppv);
 
     if (!ppv) return E_INVALIDARG;
@@ -477,7 +480,7 @@ static HRESULT WINAPI JpegDecoder_Frame_QueryInterface(IWICBitmapFrameDecode *if
         IsEqualIID(&IID_IWICBitmapSource, iid) ||
         IsEqualIID(&IID_IWICBitmapFrameDecode, iid))
     {
-        *ppv = iface;
+        *ppv = &This->IWICBitmapFrameDecode_iface;
     }
     else
     {
@@ -492,13 +495,13 @@ static HRESULT WINAPI JpegDecoder_Frame_QueryInterface(IWICBitmapFrameDecode *if
 static ULONG WINAPI JpegDecoder_Frame_AddRef(IWICBitmapFrameDecode *iface)
 {
     JpegDecoder *This = impl_from_IWICBitmapFrameDecode(iface);
-    return IUnknown_AddRef((IUnknown*)This);
+    return IWICBitmapDecoder_AddRef(&This->IWICBitmapDecoder_iface);
 }
 
 static ULONG WINAPI JpegDecoder_Frame_Release(IWICBitmapFrameDecode *iface)
 {
     JpegDecoder *This = impl_from_IWICBitmapFrameDecode(iface);
-    return IUnknown_Release((IUnknown*)This);
+    return IWICBitmapDecoder_Release(&This->IWICBitmapDecoder_iface);
 }
 
 static HRESULT WINAPI JpegDecoder_Frame_GetSize(IWICBitmapFrameDecode *iface,
@@ -722,8 +725,8 @@ HRESULT JpegDecoder_CreateInstance(IUnknown *pUnkOuter, REFIID iid, void** ppv)
     InitializeCriticalSection(&This->lock);
     This->lock.DebugInfo->Spare[0] = (DWORD_PTR)(__FILE__ ": JpegDecoder.lock");
 
-    ret = IUnknown_QueryInterface((IUnknown*)This, iid, ppv);
-    IUnknown_Release((IUnknown*)This);
+    ret = IWICBitmapDecoder_QueryInterface(&This->IWICBitmapDecoder_iface, iid, ppv);
+    IWICBitmapDecoder_Release(&This->IWICBitmapDecoder_iface);
 
     return ret;
 }
@@ -1219,7 +1222,7 @@ static HRESULT WINAPI JpegEncoder_QueryInterface(IWICBitmapEncoder *iface, REFII
     if (IsEqualIID(&IID_IUnknown, iid) ||
         IsEqualIID(&IID_IWICBitmapEncoder, iid))
     {
-        *ppv = This;
+        *ppv = &This->IWICBitmapEncoder_iface;
     }
     else
     {
@@ -1470,8 +1473,8 @@ HRESULT JpegEncoder_CreateInstance(IUnknown *pUnkOuter, REFIID iid, void** ppv)
     InitializeCriticalSection(&This->lock);
     This->lock.DebugInfo->Spare[0] = (DWORD_PTR)(__FILE__ ": JpegEncoder.lock");
 
-    ret = IUnknown_QueryInterface((IUnknown*)This, iid, ppv);
-    IUnknown_Release((IUnknown*)This);
+    ret = IWICBitmapEncoder_QueryInterface(&This->IWICBitmapEncoder_iface, iid, ppv);
+    IWICBitmapEncoder_Release(&This->IWICBitmapEncoder_iface);
 
     return ret;
 }