d3d8: Use unsafe_impl_from_IDirect3DVertexBuffer8 for app provided ifaces.

dlls/d3d8/buffer.c

@@ -298,6 +298,15 @@ HRESULT vertexbuffer_init(IDirect3DVertexBuffer8Impl *buffer, IDirect3DDevice8Im
     return D3D_OK;
 }
 
+IDirect3DVertexBuffer8Impl *unsafe_impl_from_IDirect3DVertexBuffer8(IDirect3DVertexBuffer8 *iface)
+{
+    if (!iface)
+        return NULL;
+    assert(iface->lpVtbl == &Direct3DVertexBuffer8_Vtbl);
+
+    return impl_from_IDirect3DVertexBuffer8(iface);
+}
+
 static inline IDirect3DIndexBuffer8Impl *impl_from_IDirect3DIndexBuffer8(IDirect3DIndexBuffer8 *iface)
 {
     return CONTAINING_RECORD(iface, IDirect3DIndexBuffer8Impl, IDirect3DIndexBuffer8_iface);

dlls/d3d8/d3d8_private.h

@@ -277,6 +277,7 @@ struct IDirect3DVertexBuffer8Impl
 
 HRESULT vertexbuffer_init(IDirect3DVertexBuffer8Impl *buffer, IDirect3DDevice8Impl *device,
         UINT size, DWORD usage, DWORD fvf, D3DPOOL pool) DECLSPEC_HIDDEN;
+IDirect3DVertexBuffer8Impl *unsafe_impl_from_IDirect3DVertexBuffer8(IDirect3DVertexBuffer8 *iface) DECLSPEC_HIDDEN;
 
 /* --------------------- */
 /* IDirect3DIndexBuffer8 */

dlls/d3d8/device.c

@@ -2005,8 +2005,8 @@ static HRESULT WINAPI IDirect3DDevice8Impl_ProcessVertices(IDirect3DDevice8 *ifa
         DWORD Flags)
 {
     IDirect3DDevice8Impl *This = impl_from_IDirect3DDevice8(iface);
+    IDirect3DVertexBuffer8Impl *dest = unsafe_impl_from_IDirect3DVertexBuffer8(pDestBuffer);
     HRESULT hr;
-    IDirect3DVertexBuffer8Impl *dest = (IDirect3DVertexBuffer8Impl *) pDestBuffer;
 
     TRACE("iface %p, src_start_idx %u, dst_idx %u, vertex_count %u, dst_buffer %p, flags %#x.\n",
             iface, SrcStartIndex, DestIndex, VertexCount, pDestBuffer, Flags);
@@ -2683,6 +2683,7 @@ static HRESULT WINAPI IDirect3DDevice8Impl_SetStreamSource(IDirect3DDevice8 *ifa
         UINT StreamNumber, IDirect3DVertexBuffer8 *pStreamData, UINT Stride)
 {
     IDirect3DDevice8Impl *This = impl_from_IDirect3DDevice8(iface);
+    IDirect3DVertexBuffer8Impl *streamdata = unsafe_impl_from_IDirect3DVertexBuffer8(pStreamData);
     HRESULT hr;
 
     TRACE("iface %p, stream_idx %u, buffer %p, stride %u.\n",
@@ -2690,8 +2691,7 @@ static HRESULT WINAPI IDirect3DDevice8Impl_SetStreamSource(IDirect3DDevice8 *ifa
 
     wined3d_mutex_lock();
     hr = wined3d_device_set_stream_source(This->wined3d_device, StreamNumber,
-            pStreamData ? ((IDirect3DVertexBuffer8Impl *)pStreamData)->wineD3DVertexBuffer : NULL,
-            0/* Offset in bytes */, Stride);
+            streamdata ? streamdata->wineD3DVertexBuffer : NULL, 0/* Offset in bytes */, Stride);
     wined3d_mutex_unlock();
 
     return hr;