Grass Dynamics

State-of-the-art 3D games and realtime simulations demonstrate the power of currently available graphics hardware for rendering exciting natural sceneries in real-time. As nature scenes often include a lot of plants (blades of grass, shrubs, trees etc.) the rendering of a large number of them is still challenging. Furthermore, they cannot be displayed with complex geometry in real time. Many of the approaches make use of billboard representations to preserve the real-time constraint while leaving out user interaction. In general, static level design is more and more replaced by dynamic environments that can be modified in real-time throughout the gaming process. Due to the fact that natural phenomena are better approximated in the game, the player feels a higher immersion while playing. Consequently, the dynamic environment is becoming a part of the game logic: Trees are chopped to clear the path and objects need to be moved in order to fulfill quests. The more the realism of the scene is enhanced the more of the player's expectations are satisfied. Following this trend, our paper takes dynamic environments one step further by integrating responsive real-time simulation of ground vegetation. We propose a highly efficient technique for GPU-based simulation of responsive grass billboards. Our implementation targets Shader Model 4 graphics boards, including geometry shaders and stream output. The collision detection with dynamic scene objects, the response and the recovering are directly simulated on the GPU. An adaptive geometrical representation of the grass guarantes a pleasing visual rendering in conjunction with a high performance. Thus, the responsive grass approach has the potential to significantly improve the challenges in game play of modern games and may lead to a better perception of interactive environments.

Results

Realtime simulation of grass fields on the GPU:

GPU-based Responsive Grass

Large natural environments are often essential for todays computer games. Interaction with the environment is widely implemented in order to satisfy the player’s expectations of a living scenery and to help increasing the immersion of the player. Within this context our work describes an efficient way to simulate a responsive grass layer with todays graphics cards in real-time. Clumps of grass are approximated by two billboard representations. GPU-based distance maps of scene objects are employed to test for penetrations and for resolving them. Adaptive refinement is necessary to preserve the shape of deformed billboards. A recovering process is applied after the deformation which restores the original that is to say the undeformed and efficient shape. The primitives of each billboard are assembled during the rendering process. Their vertices are dynamically lit within an ambient occlusion based irradiance volume. Alpha-to-Coverage completes the illusion as it is used to simulate the semitransparent nature of grass.

Paper Presentation Bibtex