The past couple of weeks have been super busy at work, but I’ve still managed to get the ball rolling with the new renderer for the Vortex Engine.
This is the first time in years I’ve decided to actually write a completely new renderer for Vortex. This new renderer is a complete clean-room implementation of the rendering logic, designed specifically for the new Entity-Component system in the engine.
Current Rendering Systems in Vortex
Let’s start by taking a look at the current rendering systems in the Vortex Engine. Ever since 2011, Vortex has had two rendering systems: a Fixed Pipeline rendering system and a Programmable Pipeline rendering system.
Dual Pipeline support: a Comparison of the Rendering Pipelines available in Vortex Engine. The image on the left represent the Fixed Pipeline. The image on the right represents the Programmable Pipeline.
Both these rendering systems are pretty robust. Both have been used to develop and launch successful apps in the iOS App Store and they have proven to be reliable and portable, allowing the programmer to target Linux, Windows, Mac OS X and Android, as well as iOS.
The problem with these renderers is that they were designed with Vortex’s Scenegraph-based API in mind. This means that these renderers do not know anything about Entities or Components, but rather, they work at the Node level.
Moving forward, the direction for the Vortex Engine is to provide an Entity Component interface and move away from the Scenegraph-based API. This means that glue code has to be developed to allow the traditional renderers to draw the Entity-Component hierarchy.
So… why is this a problem?
Why a new Renderer?
As Vortex V3 now provides a brand new Entity-Component hierarchy for expressing scenes, glue code had to be developed in order to leverage the legacy renderers in the Vortex Editor. In the beginning this was not a major problem, however, as the Entity-Component system matures, it’s become ever more difficult to maintain compatibility with the legacy renderers.
PBR Materials in Unreal Engine 4. Image from ArtStation’s Pinterest.
Another factor is the incredible pace at which the rendering practice has continued to develop in these past few years. Nowadays, almost all modern mobile devices have support for OpenGL ES 2.0 and even 3.0, and PBR rendering has gone from a distant possibility to a very real technique for mobile devices. Supporting PBR rendering on these legacy renderers would require a significant rewrite of their core logic.
Finally, from a codebase standpoint, both renderers were implemented more than 5 years ago, back when C++11 was just starting to get adopted and compiler support was very limited. This does not mean that the legacy renderers’ codebases are obsolete by any means, but by leveraging modern C++ techniques, they could be cleaned up significantly.
From all of this, it is clear that a new clean-room implementation of the renderer is needed.
Designing a New Renderer
The idea is for the new renderer to be able to work with the Entity-Component hierarchy natively without a translation layer. It should be able to traverse the hierarchy and determine exactly what needs to be rendered for the current frame.
Once the objects to be renderer have been determined, then, a new and much richer material interface would determine exactly how to draw each object according to its properties.
Just like with the Vortex 2.0 renderer, this new renderer should fully support programmable shaders, but through a simplified API that requires less coding and allows drawing much more interesting objects and visual effects.
Choosing a backing API
Choosing a rendering API used to be a simple decision: pick DirectX for Windows-only code or OpenGL (ES) for portable code. The landscape has changed significantly in the past few years, however, and there are now a plethora of APIs we can choose from to implement hardware-accelerated graphics.
This year alone, the Khronos Group released the Vulkan specification, a new API that tackles some of the problems inherent to OpenGL, as seen in the following image.
Comparison of the OpenGL and Vulkan APIs of the Khronos Group. Slide Copyright (C) 2016 Khronos Group.
Now, both Vulkan and Metal are very appealing low-level APIs that provide a fine degree of control over the hardware, but they are limited in the sense that while Metal is Apple specific, Vulkan is cross-platform but not available on Apple devices.
DirectX 12 is Windows 10 only and that discards it right off the bat (for this project at least). DirectX 11 is a good option but, again, Windows only.
This leaves OpenGL and OpenGL ES as the two remaining options. I’ve decided to settle for Core OpenGL 3.3 at this time. I think it’s an API that exposes enough modern concepts to allow implementing a sophisticated renderer while also remaining fully compatible with Windows, iOS and everything in-between.
I don’t discard the possibility in the future of implementing a dedicated Metal or Vulkan backend for Vortex, and nothing in the Engine design should prevent this from happening, however, at this time, we have to start on a platform that’s available everywhere.
Using Core OpenGL 3.3 will also allow reusing the battle-tested shader API in Vortex. This component has several years of service under its belt and I’d risk to say that all of its bugs have been found and fixed.
Other than this particular component, I’m also reusing the material interface (but completely overhauling it) and developing a new RetainedMesh class for better handling mesh data streaming to the GPU.
Writing a comprehensive renderer is no weekend task. A lot of components must be carefully designed and built to fit together. The room for error is minimal, and any problem in any component that touches anything related to the Video Card can potentially make the entire system fail.
It is, at the same time, one of the most satisfying tasks that I can think of as a software engineer. Once you see it come to life, it’s more than a sum of its parts: it’s a platform for rendering incredible dream worlds on a myriad of platforms.
I will take my time developing this new renderer, enjoying the process along the way.
Stay tuned for more! : )