1. Computer Graphics and Multimedia Systems, University of Siegen, Germany 1 GPU-Based Responsive Grass Jens Orthmann, Christof Rezk-Salama, Andreas Kolb

2. Computer Graphics and Multimedia Systems, University of Siegen, Germany 2 Overview Motivation Grass Representation Collision Handling Rendering Results Future Work

3. Computer Graphics and Multimedia Systems, University of Siegen, Germany 3 Motivation Physically correct reacting environment improves immersion for players Until now: research has been focused on the animation and rendering Modern graphics cards  shift the workload to the GPU

4. Computer Graphics and Multimedia Systems, University of Siegen, Germany 4 Grass Billboards Usually: Clumps of grass are approximated by billboards  quad with a semi-transparent texture Crossed billboards produce a more volumetric impression

5. Computer Graphics and Multimedia Systems, University of Siegen, Germany 5 CPU-Based Predecision The grass layer is organized in an octree A lookup into the octree brings up colliding nodes Affected billboards will be handled on the GPU

6. Computer Graphics and Multimedia Systems, University of Siegen, Germany 6 GPU-Based Collisionhandling Collision detection and reaction requires a more detailed mesh Collisions are detected and resolved per vertex Mass-spring system preserves the shape Performance stability via recovering Animation + Refinement Collision- detection Collision- reaction RecoveringSimplification

7. Computer Graphics and Multimedia Systems, University of Siegen, Germany 7 Depth Cubes Objects are implictly represented by depth-cubes The mesh is projected to each face Each face stores the distance to the surface and the normal information

8. Computer Graphics and Multimedia Systems, University of Siegen, Germany 8 Collision Detection Vertex collides if it is occluded by all six faces of the depth cube Occlusion is determined by a lookup within the depth cube The accuracy of the detection depends on the resolution of the depth cube

9. Computer Graphics and Multimedia Systems, University of Siegen, Germany 9 Collision Reaction The normal vector within the depth cube defines the reaction‘s direction The vertex then is moved along the normal out of the object As each vertex is handled separately unrealistic distortions may occur

10. Computer Graphics and Multimedia Systems, University of Siegen, Germany 10 Shape Preservation Spring model preserves the overall shape Topology information is required Length constraints correct adjacent vertices

11. Computer Graphics and Multimedia Systems, University of Siegen, Germany 11 Recovering Previously collided billboards will regenerate Interpolation between deformed and undeformed shape Billboards will be simplified after regeneration deformed undeformed

12. Computer Graphics and Multimedia Systems, University of Siegen, Germany 12 Irradiance Information Ambient occlusion: How much light reaches a point and from which direction? Amount and mean-direction are determined by using shadow maps Sampling an environment map results in the irradiance

13. Computer Graphics and Multimedia Systems, University of Siegen, Germany 13 Rendering Irradiance information is precomputed for the complete grass layer During runtime: tri-linear interpolation within the volume results in the irradiance

14. Computer Graphics and Multimedia Systems, University of Siegen, Germany 14 Alpha-To-Coverage The transparency of a pixel determines how much sub-samples are colored The final color is calculated during the multi-sample resolve phase Quality depends on the multi-sampling resolution

15. Computer Graphics and Multimedia Systems, University of Siegen, Germany 15 Results Video

16. Computer Graphics and Multimedia Systems, University of Siegen, Germany 16 Future Work Take dynamic environments one step further Enables integration of new game elements and extends game logics Apply responsive grass algorithm to small plants like bushes, shrubs… Improvement of visual results by dynamic sub-divisions

17. Computer Graphics and Multimedia Systems, University of Siegen, Germany Thank You Thank you for your attention 17