Thursday, 2 December 2010

Animated Random Access Vector Graphics

I have just finished my Honours degree and the topic of my thesis is "Random Access Rendering of Animated Vector Graphics Using GPU". It is based on previous work by Nehab & Hoppe. Full paper of my thesis is available here.

The meaning of "random access" here is similar to when used in term random-access memory (RAM). It means that the color of the image can be queried at an arbitrary coordinate within the image space. Efficient random access to image data is essential for texture mapping, and has been traditionally associated with raster images.

The novel approach to random access rendering introduced by Nehab & Hoppe is to preprocess the vector image, localize the data into cells, and build a fast look-up structure used for rendering. In short, it allows efficient texture mapping of vector images onto curved surfaces. However, their CPU localisation was way too slow to be used in real time with animated vector images.

My goal was to improve their approach of vector image localisation by parallelizing the encoding algorithm and implementing it on the GPU to take full advantage of its parallel architecture, thus allowing application to animated images. In my thesis, I present an alternative look-up structure, more suitable to parallelism, and an efficient parallel encoding algorithm. I was able to achieve significant performance improvements in both encoding and rendering stages. In most cases, my rendering approach even outperforms the traditional forward rendering approach.

Wednesday, 1 December 2010

Game Engine

Over the last few years, while studying Games & Graphics Programming at RMIT, I was also working on my own game engine as one of my hobby projects. A complete game engine is a complex beast which includes many subsystems including rendering, animation, sound, physics, AI, resource management, exporting pipeline and more. Trying to implement everything from scratch would be simply a crazy idea, therefore I mostly focused on three objectives.

This demo is available for download here:

Firstly, I wanted to implement a modern renderer with state-of-art visual effect. Secondly, I wanted to implement an animation system supporting both skeletal and cutscene (scene-wide) animations. Finally, I wanted to implement a content pipeline for models, animations and scenes (maps), to bring resources from content creation software such as Maya into the game engine.

I have followed the trend of many other recent game engines and decided to implement deferred rendering, which allows me to use complex lighting scenarios with hundreds of lights and still render the scene efficiently. This approach also turned out to lend itself nicely to implementation of depth-of-field effect. I also implemented a High-Dynamic-Range lighting pipeline with tone mapping and "Bloom" effect.

I used Maya SDK to create a custom exporter tool. By using Maya's C++ API I was able to link the plugin executable directly to my engine library, allowing me to use the engine's serialization functions. My exporter was somewhat inspired by that of UnrealEd and allows separate exporting of static meshes, skeleton poses or character animations. However, since I wasn't going to develop my own editor software, I implemented additional exporting functions for scene-wide animations, allowing construction of cutscene sequences. The exporter encodes all these resources into package files which can be directly loaded by the engine.

In 3rd year of uni I took the opportunity to use my game engine in the major project. I teamed up with a couple of digital artists and designers to produce a short demo in the form of an intro to what would be a game similar to Heavy Rain. We tried to use the features of the rendering engine creatively, such as utilizing the depth-of-field effect to steer the player's attention towards an interactive object.

In order to avoid combinatorial explosion in shading code arising from many different material and geometry types, I implemented an automatic shader compositor. It is designed as a data-driven graph system, where inter-connected processing nodes are defined by their input data, output data and shading code. Every asset in the pipeline can register its own shading nodes which get automatically inserted into the shading graph based on the flow of data through the network. The automatic shader compositor makes it easy to combine different types of materials with various number of input textures and shading modes such as diffuse map, normal map and cell shading, as well as additional geometry processing such as hardware skinning.

Overall, I am quite satisfied with the work I've done on the engine so far. I have achieved my goal of implementing some of the state-of-art visual effects as well as the supporting asset pipeline and learned a lot in the process. In the future, I might add more to it, either in the form of additional rendering effects or optimizations and improvement of existing techniques. In particular, I am planning to implement screen-space ambient occlusion and explore alternative shadowing approaches (simple shadow maps turn out quite bad more often than not).