Drawing with a Custom Camera

Gum's render loop is driven by an internal camera (SystemManagers.Default.Renderer.Camera). The auto-fit helpers — EnableZoomToWindow and EnableExpandToWindow — are the easiest way to drive that camera, but games that already maintain their own camera state (for pan / zoom / cinematic effects, or because other content draws under the same camera) need a way to hand Gum that state directly.

The Draw method on GumService has platform-specific overloads that accept the platform's native per-frame camera type, copy the relevant fields onto Gum's internal camera, and then draw under it. This is the supported path for "render Gum under my own camera."

raylib: Draw(Camera2D)

On raylib, GumService.Draw accepts a raylib Camera2D:

using Raylib_cs;
using static Raylib_cs.Raylib;

GumService GumUI => GumService.Default;

Camera2D camera = new Camera2D
{
    Target = new Vector2(0, 0),
    Offset = new Vector2(0, 0),
    Zoom = 1f,
    Rotation = 0,
};

while (!WindowShouldClose())
{
    // ...handle input that mutates camera.Target / camera.Zoom...

    BeginDrawing();
    ClearBackground(Color.Black);

    BeginMode2D(camera);
    DrawWorld();       // your own world content under the same camera
    EndMode2D();

    GumUI.Update(GetTime());
    GumUI.Draw(camera); // Gum renders under the same Camera2D
    EndDrawing();
}

The overload copies camera.Target.X, camera.Target.Y, and camera.Zoom onto Gum's internal camera before drawing.

camera.Offset and camera.Rotation are intentionally not copied:

• Offset — Gum derives the rendering offset from Camera.CameraCenterOnScreen (Center or TopLeft). Set that separately on the camera if you need non-default placement; the offset on the passed Camera2D is ignored.
• Rotation — Gum's camera does not model rotation. A rotated Camera2D will not produce rotated UI from this call. If you need rotated UI input compensation, see Cursor TransformMatrix.

Each call to Draw(camera) overwrites any previously-configured X, Y, and Zoom on Gum's internal camera for that frame, so this overload and the auto-fit helpers (EnableZoomToWindow / EnableExpandToWindow) should not be used together — the camera passed to Draw wins.

Other platforms

Equivalent Draw overloads for MonoGame, KNI, FNA, and SkiaSharp are not yet shipped. The current workaround on those backends is the RenderTarget approach — render Gum into a RenderTarget2D, then composite it under your own transform. As the per-platform overloads land they will follow the same pattern: pass the platform's native per-frame transform to GumUI.Draw, no separate sync step.