d3d9: Use unsafe_impl_from_IDirect3DIndexBuffer9 for an app provided iface.

dlls/d3d9/buffer.c

@@ -19,6 +19,7 @@
  */
 
 #include "config.h"
+#include <assert.h>
 #include "d3d9_private.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(d3d9);
@@ -573,3 +574,12 @@ HRESULT indexbuffer_init(IDirect3DIndexBuffer9Impl *buffer, IDirect3DDevice9Impl
 
     return D3D_OK;
 }
+
+IDirect3DIndexBuffer9Impl *unsafe_impl_from_IDirect3DIndexBuffer9(IDirect3DIndexBuffer9 *iface)
+{
+    if (!iface)
+        return NULL;
+    assert(iface->lpVtbl == &d3d9_indexbuffer_vtbl);
+
+    return impl_from_IDirect3DIndexBuffer9(iface);
+}

dlls/d3d9/d3d9_private.h

@@ -283,6 +283,7 @@ typedef struct IDirect3DIndexBuffer9Impl
 
 HRESULT indexbuffer_init(IDirect3DIndexBuffer9Impl *buffer, IDirect3DDevice9Impl *device,
         UINT size, DWORD usage, D3DFORMAT format, D3DPOOL pool) DECLSPEC_HIDDEN;
+IDirect3DIndexBuffer9Impl *unsafe_impl_from_IDirect3DIndexBuffer9(IDirect3DIndexBuffer9 *iface) DECLSPEC_HIDDEN;
 
 /* --------------------- */
 /* IDirect3DBaseTexture9 */

dlls/d3d9/device.c

@@ -2528,8 +2528,8 @@ static HRESULT WINAPI IDirect3DDevice9Impl_SetIndices(IDirect3DDevice9Ex *iface,
         IDirect3DIndexBuffer9 *pIndexData)
 {
     IDirect3DDevice9Impl *This = impl_from_IDirect3DDevice9Ex(iface);
+    IDirect3DIndexBuffer9Impl *ib = unsafe_impl_from_IDirect3DIndexBuffer9(pIndexData);
     HRESULT hr;
-    IDirect3DIndexBuffer9Impl *ib = (IDirect3DIndexBuffer9Impl *) pIndexData;
 
     TRACE("iface %p, buffer %p.\n", iface, pIndexData);