dxgi: Reset the back buffer index to zero on ResizeBuffers().

dlls/dxgi/swapchain.c

@@ -2249,6 +2249,8 @@ static HRESULT d3d12_swapchain_resize_buffers(struct d3d12_swapchain *swapchain,
     if (!dxgi_validate_swapchain_desc(&new_desc))
         return DXGI_ERROR_INVALID_CALL;
 
+    swapchain->current_buffer_index = 0;
+
     if (desc->Width == new_desc.Width && desc->Height == new_desc.Height
             && desc->Format == new_desc.Format && desc->BufferCount == new_desc.BufferCount)
         return S_OK;

dlls/dxgi/tests/dxgi.c

@@ -4988,7 +4988,6 @@ static void test_swapchain_backbuffer_index(IUnknown *device, BOOL is_d3d12)
         {
             index = IDXGISwapChain3_GetCurrentBackBufferIndex(swapchain3);
             expected_index = is_d3d12 ? j % swapchain_desc.BufferCount : 0;
-            todo_wine_if(is_d3d12)
             ok(index == expected_index, "Got back buffer index %u, expected %u.\n", index, expected_index);
             hr = IDXGISwapChain3_Present(swapchain3, 0, 0);
             ok(hr == S_OK, "Got unexpected hr %#lx.\n", hr);
@@ -5003,7 +5002,6 @@ static void test_swapchain_backbuffer_index(IUnknown *device, BOOL is_d3d12)
         {
             index = IDXGISwapChain3_GetCurrentBackBufferIndex(swapchain3);
             expected_index = is_d3d12 ? j % swapchain_desc.BufferCount : 0;
-            todo_wine_if(is_d3d12)
             ok(index == expected_index, "Got back buffer index %u, expected %u.\n", index, expected_index);
             hr = IDXGISwapChain3_Present(swapchain3, 0, 0);
             ok(hr == S_OK, "Got unexpected hr %#lx.\n", hr);
@@ -5017,7 +5015,6 @@ static void test_swapchain_backbuffer_index(IUnknown *device, BOOL is_d3d12)
         {
             index = IDXGISwapChain3_GetCurrentBackBufferIndex(swapchain3);
             expected_index = is_d3d12 ? j % swapchain_desc.BufferCount : 0;
-            todo_wine_if(is_d3d12)
             ok(index == expected_index, "Got back buffer index %u, expected %u.\n", index, expected_index);
             hr = IDXGISwapChain3_Present(swapchain3, 0, 0);
             ok(hr == S_OK, "Got unexpected hr %#lx.\n", hr);