The problem is pretty complex, though, so I figured a short blogpost would be needed to really explain it. In short, this is the question:
What is the most efficient way to synchronise renderable objects between the game thread and the render thread?
There are a couple of subtleties you need to know to answer this for our situation, though. Let me start with a scheme that shows the approach to threading in the Ronitech (our in-house multiplatform 2D engine), as we use it in Awesomenauts on the Xbox 360 and Playstation 3:
This works fine and we managed to get 60fps on console this way. However, the copying phase takes relatively long, so I am still wasting a lot of performance there. Since we will also use the Ronitech in all our future games, improving here will pay off greatly in our future projects.
There are a couple of specific requirements that I have to make this work with the rest of our engine:
- The gameplay thread must be able to modify (and even delete!) all renderable objects. At the same time, the renderer must still be able to render each object how it looked during the previous frame.
- Within a single frame, the same object might be rendered to different viewports in different ways. For example, a character might be partially transparent in one viewport and fully visible in another. The game can register itself as a PreViewportRenderListener and thus change objects in between the rendering of two viewports.
So, what alternatives are there to just copying all the relevant data for all visible objects every frame? Or should rendering in a separate thread be set up differently all together? Please comment below if you have interesting ideas for this!