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Render Module

Session::Render() is the foundation for overlays: it tells you which renderer the client uses, hands you the device, and marks the frame boundaries.

Renderer information​

std::optional< RendererID > GetRendererID() const;
std::optional< Uint64 > GetDeviceHandle() const;

GetRendererID() returns OpenGL or DirectX11. GetDeviceHandle() returns the backend device as an address; cast it per renderer:

  • DirectX 11: the value is an ID3D11Device *.
  • OpenGL: there is no device object; the value is 0.
if( g_session->Render().GetRendererID() == TruckersMP::RendererID::DirectX11 )
{
    if( auto d3d = reinterpret_cast< ID3D11Device * >( g_session->Render().GetDeviceHandle().value_or( 0 ) ) )
    {
        InitMyOverlay( d3d );
    }
}

Frame events​

Event<> OnPreRender;
Event<> OnPostRender;

The two events bracket the TruckersMP GUI within the frame:

  • OnPreRender fires before the TruckersMP GUI renders. Drawing here puts your output under the client's own UI.
  • OnPostRender fires after the TruckersMP GUI has rendered. Drawing here puts your output on top of everything, which is what most overlays want.
g_session->Render().OnPostRender.Register( []
{
    if( g_overlayOpen )
    {
        DrawMyOverlay();
    }
} );

Working with the device​

Two rules keep overlay code safe:

  • Draw only inside the frame events. The device is in a known state there; touching it at other times races the game's or client's own rendering.
  • Restore the state you change. A plugin that renders anything is expected to put the device back the way it found it before returning; the client does not re-assert its full pipeline state around your callback.

Popular immediate-mode UI libraries (such as Dear ImGui with the D3D11 backend) fit this model directly: initialize them with the device from GetDeviceHandle(), feed them from the Input module, and render them in OnPostRender.