Render Pipelines

A render pipeline (just called a Pipeline in the API) is a combination of a Stage, Camera and some kind of render target (often the framebuffer) which controls the visual output of your scene. Pipelines can be combined to "layer up" the finally displayed frame.

Pipelines are controlled by the Compositor which is a property of the Window and each frame are run in order to generate the final image. For example, if you want to create a 3D scene, with a 2D UI layer you may do the following:

  1. Create a Stage and a perspective Camera for the 3D portion
  2. Create a Stage and an orthographic Camera for the UI
  3. Create a Pipeline to render the 3D scene using the perspective camera
  4. Create a Pipeline to render the UI using the orthographic camera, but with a higher RenderPriority than the 3D scene

This is how it might look in code:

auto stage = window->new_stage();
auto persp_camera = stage->new_camera();

auto overlay = window->new_stage();
auto ortho_camera = overlay->new_camera();

auto pipeline1 = compositor->render(stage, persp_camera);
auto pipeline2 = compositor->render(
    overlay, ortho_camera


Now StageNodes added to stage will be rendered in 3D before UI elements added to overlay.

Linking Pipelines to Stages

Often you will build up your scenes in the load() method of your Scene subclass. It's probable that this scene building will happen in a background thread. Activating pipelines in load() in this scenario is dangerous as any stage that's attached to an activated Pipeline will be updated in the main thread which will cause deadlocks and crashes if you're also manipulating it concurrently. It's advised that you activate your pipelines in your Scene's activate() method, and that you deactivate them in your Scene's deactivate() method.

This boilerplate overriding of Scene::activate() and Scene::deactivate() can become repetitive, so Simulant provides a helper method called Scene::link_pipeline. Once you link a Pipeline to a Scene it will activate and deactivate along with it.

auto pipeline1 = compositor->render(stage, persp_camera);
link_pipeline(pipeline1); // pipeline1 will activate when this Scene is activated

Naming Pipelines

Pipelines are Nameable meaning that you can set a name and then find them later by that name:

compositor->render(stage, camera)->set_name("pipeline1");

auto p1 = window->find_pipeline("pipeline1");

If there is no pipeline with that name, then you will get a null PipelinePtr returned.