d3d11: Implement d3d11_immediate_context_IAGetIndexBuffer().

dlls/d3d11/device.c

@@ -1344,7 +1344,26 @@ static void STDMETHODCALLTYPE d3d11_immediate_context_IAGetVertexBuffers(ID3D11D
 static void STDMETHODCALLTYPE d3d11_immediate_context_IAGetIndexBuffer(ID3D11DeviceContext *iface,
         ID3D11Buffer **buffer, DXGI_FORMAT *format, UINT *offset)
 {
-    FIXME("iface %p, buffer %p, format %p, offset %p stub!\n", iface, buffer, format, offset);
+    struct d3d_device *device = device_from_immediate_ID3D11DeviceContext(iface);
+    enum wined3d_format_id wined3d_format;
+    struct wined3d_buffer *wined3d_buffer;
+    struct d3d_buffer *buffer_impl;
+
+    TRACE("iface %p, buffer %p, format %p, offset %p.\n", iface, buffer, format, offset);
+
+    wined3d_mutex_lock();
+    wined3d_buffer = wined3d_device_get_index_buffer(device->wined3d_device, &wined3d_format, offset);
+    *format = dxgi_format_from_wined3dformat(wined3d_format);
+    if (!wined3d_buffer)
+    {
+        wined3d_mutex_unlock();
+        *buffer = NULL;
+        return;
+    }
+
+    buffer_impl = wined3d_buffer_get_parent(wined3d_buffer);
+    wined3d_mutex_unlock();
+    ID3D11Buffer_AddRef(*buffer = &buffer_impl->ID3D11Buffer_iface);
 }
 
 static void STDMETHODCALLTYPE d3d11_immediate_context_GSGetConstantBuffers(ID3D11DeviceContext *iface,