sokol_app.h: add function to query IDXGISwapChain object

sokol_app.h

@@ -1489,6 +1489,8 @@ SOKOL_APP_API_DECL const void* sapp_ios_get_window(void);
 SOKOL_APP_API_DECL const void* sapp_d3d11_get_device(void);
 /* D3D11: get pointer to ID3D11DeviceContext object */
 SOKOL_APP_API_DECL const void* sapp_d3d11_get_device_context(void);
+/* D3D11: get pointer to IDXGISwapChain object */
+SOKOL_APP_API_DECL const void* sapp_d3d11_get_swap_chain(void);
 /* D3D11: get pointer to ID3D11RenderTargetView object */
 SOKOL_APP_API_DECL const void* sapp_d3d11_get_render_target_view(void);
 /* D3D11: get pointer to ID3D11DepthStencilView */
@@ -10949,6 +10951,15 @@ SOKOL_API_IMPL const void* sapp_d3d11_get_device_context(void) {
     #endif
 }
 
+SOKOL_API_IMPL const void* sapp_d3d11_get_swap_chain(void) {
+    SOKOL_ASSERT(_sapp.valid);
+#if defined(SOKOL_D3D11)
+    return _sapp.d3d11.swap_chain;
+#else
+    return 0;
+#endif
+}
+
 SOKOL_API_IMPL const void* sapp_d3d11_get_render_target_view(void) {
     SOKOL_ASSERT(_sapp.valid);
     #if defined(SOKOL_D3D11)