Friday, December 18, 2015

Data Driven Rendering in Stingray


We’re all familiar with the benefits that a data driven architecture brings to gameplay: code is decoupled from data, enabling live linking and rapid iteration. Placing new objects in the editor or modifying the speed of a character has an immediate effect on a live game instance. Really speeds up the development process as you fine tune scripts, gameplay and other content.

What about graphics programming?  It turns out that the same architecture and associated benefits apply to Stingray’s renderer.

Just by modifying configuration files (albeit somewhat complex configuration files) we can implement new shader programs, post-processing effects and even different cascading shadow map implementations. All in real time, on a live game instance. Which is a big win for graphics programmers: try out new ideas, fine tune shaders all with real-time feedback. No more of that long edit/compile/run/debug cycle. And this applies to the entire rendering pipeline: everything from the object space to world space transforms to shadow casting and the final rendering pass is all exposed as config file data, not as C++ code as with traditional architectures.

I gave a presentation on this topic a while back which has now found it’s way to our YouTube channel:

https://www.youtube.com/channel/UC0fIe6XV1PjilADTei9JMOA

By the way, there’s a lot of other great Stingray content up there so please check it out! The renderer presentation can be found under “Stingray Render Config Tutorial.”

The details as well as a PowerPoint can be found there. The code changes to add a trivial greyscale post-processing effect involve:

settings.ini: 

The render_config variable points to the renderer.config file. Settings.ini also provides a section to override default settings found in the next file, renderer.render_config

core/stingray_renderer/renderer.render_config:

Points to our shader libraries, text files containing actual shader programs. A section called global_resources allocates graphics buffers, such as scratch buffers for the cascading shadow maps and G-buffers for deferred rendering along with the main framebuffer. And most of the actual rendering is invoked in the resource_generators section. Again, more details in the YouTube video though a surprising amount can be learned just by grepping through the various config files and playing with the settings. Which is easy to do since it’s all data driven!

core/stingray_renderer/shader_libraries/development.shader_source:

One of several shader libraries. While shader code can be entered as text here, Stingray also provides a graphical node-based shader editor. And we support ShaderFX materials from Max or Maya. It’s often easier (and more portable) to implement shaders graphically.

But whatever method you choose to implement shaders in, the key point is that Stingray's entire rendering pipeline is fully accessible through configuration files. With our data driven architecture making complex rendering changes, while still non-trivial, is a whole lot faster and easier (and portable!) than working with platform-specific C++ code.

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