FORSCHUNG & ENTWICKLUNG: Akkurate Darstellung transparenter Objekte bei 3D-Anwendungen

Fabian Friederichs: Die akkurate Darstellung transparenter Objekte ist nach wie vor eine Herausforderung für aktuelle Frameworks und Engines für interaktive 3D-Anwendungen. Transparenz ist beispielsweise unerlässlich im Computer-Aided Design. Auch virtuelle Spielwelten erhalten einen Großteil ihrer Immersion durch Anwendung von Transparenzeffekten zur Darstellung von Vegetation oder volumetrischen Phänomenen wie Feuer, Rauch oder Nebel. Mit Rendertechniken für 3D-Anwendungen und 3D-Engines hat sich der Autor Fabian Friedrichs in seiner Bachelorarbeit „Improving Order-Independent Transparency“ befasst. Für seine Forschung wurde er mit dem Hochschulabsolventenpreis der FKTG ausgezeichnet.

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Order independent transparency is still not widely adopted in current productiongrade engines and frameworks for interactive 3D applications, which imposes severe limitations on the use of transparent or translucent objects and materials. Existing truly order independent blending operators, namely the work of Meshkin [2007], Bavoil and Myers [2008] and McGuire and Bavoil [2013] produce already promising results for low to medium opacity values but lack accuracy regarding visual occlusion information when it comes to more opaque surfaces. This thesis aims to improve that accuracy by dividing the scene into a fixed number of depth buckets, applying the operator of McGuire and Bavoil to all of these and combining the results using correct alpha blending. Interpolation and a depth buffer offset technique, already used successfully for reducing artifacts of Opacity Maps [Yuksel and Keyser 2008], are applied to reduce resulting layering artifacts. Furthermore, two methods for distributing fragments to the buckets are evaluated. Various combinations of the two distribution methods and variants of the new algorithm are tested in five scenes with varying geometric and depth complexity. The results show a significant improvement of visual quality for surfaces of medium to high opacity at reasonable render times for interactive applications. However, layering artifacts are still present in some situations and both tested distribution methods are rather inefficient in scenes which combine very high depth and geometric complexity.