Transparency and Anti-Aliasing Techniques for Real-Time Rendering

Marilena Maule (UFRGS), Rafael Torchelsen (UFFS), Rui Bastos (NVIDIA), João L. D. Comba (UFRGS)
InSIBGRAPI Conference on Graphics Patterns and Images (Tutorials), 2012, Brazil

Transparency and anti-aliasing effects are crucial to enhance the realism in computer-generated images. In common, both effects have the fact they rely on processing discrete samples from a given function, but using the samples for different purposes. For transparency computation, samples usually encode color information along a ray that crosses a scene, which are combined in order of intersection to produce the final color of a pixel. For anti-aliasing, samples usually represent different color contributions within the region of a pixel, and must be combined with the proper weights to produce the final color of a pixel. Graphics applications have a high demand for such effects. Transparency effects are largely used to render transparent objects in CAD models, and several other phenomena, such as hair, smoke, fire, rain, grass, etc. Anti-aliasing is an even more crucial effect, because jagged edges can be easily spotted and create disruptive distractions during a 3D walkthrough, and clearly are unacceptable in real-time applications. For algorithms that compute these effects, there are several factors that impact the quality and performance of the final result. For example, a simple transparency effect can be simulated using pre-computed textures, sorted in depth order. However, more complex transparent effects, which require a higher cost for processing transparency samples in depth ordering, are often too costly to be included in interactive 3D applications, like games. This scenario is changing with the improvement in performance of GPUs, but transparency effects still have to fight for the computational power with the other aspects of the application. Similarly, anti-aliasing (AA) techniques are directly impacted by the need to collect and process multiple samples. There is a vast number of proposals in the image processing literature that describes how to solve the problem, each with its own tradeoffs on quality and performance. Likewise, GPUs are often used to improve performance of AA algorithms, and some already have AA support in hardware. While good results with respect to quality and performance are obtained for static scenes, to maintain temporal coherence (coherence between frames) is still challenging, especially when relying only in the color information. In this tutorial we review state-of-the-art techniques for transparency and anti-aliasing effects. Their initial ideas and subsequent GPU accelerations are detailed, with a discussion on their strengths and limitations. We conclude with a discussion on applications and methods that can arise in the future.



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