Graph retained or reconstructed?

[sphet]

In the common case, is the graph created for rendering reconstructed from scratch every frame, or expected to be updated each frame?

[vsg-dev]

The VulkanSceneGraph doesn't have a graph that is created for rendering each frame.

There is the main scene graph that is traversed each frame by the RecordTraversal that records Vulkan commands to vk/vsg::CommandBuffer which are then submitted to the vk/vsg::Queue each frame.

The command buffers are re-recorded each frame unless you are using a SecondaryCommandGraph/ExecuteCommands to reuse recorded command buffers.

Does this answer you question? As the way asked makes it seem like you've got a preconception of what the VSG might be doing.

In general, it's best to explain what you are trying to achieve as an end result and ask us how you want to achieve it, then have us fill in the blanks, rather than say stuff that has us guessing what ideas might be in your head in order to address those.

[sphet]

I apologize for not being clear. I am researching scene graphs generally, and was trying to understand if the main graph in vsg is meant to be manipulated by the application state, and then traversed each time a frame need rendering via the RecordTraversal. I really appreciate the well-written code and the performance decisons made here. I think you have answered my question, thanks.

[robertosfield]

The bulk of scene graph state is typically static, with the view's camera changing the view frustum and affecting what gets culled during each RecordTraversal.

In applications where there are animations or other updates happening then those parts of the scene graph will be updated, perhaps every frame. Done right this will just require a small amount of dynamic data to be transferred between the CPU and GPU each frame.

With more rendering techniques like shadows and other multi-pass/multistage rendering techniques the VSG's RecordTraversal can record multiple command buffers and then submit them together with ordering enforced to make sure the nested RTT command buffers get rendered before the main rendering happens.

Some multi-stage techniques might be managed explicitly at the top level with compute and graphics stages, or for work to be done implicitly by the VSG, like when users enable shadows on lights and the shadow mapping backend it fired up on demand. The lighting uniforms and shadow mapping is managed by the ViewDependetState.

The VSG also allows applications to render multiple views on a single window, or spread across multiple windows. To do this one sets up a high level graph that sits above the View's which sit about the scene graphs elements. This means you have graph elements above the scene graph, and graph elements below the scene graph.