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GPU- Based Responsive Grass

This paper presents a new approach to rendering grass using GPU-based techniques to improve player immersion through physically accurate interactions with the environment. By utilizing modern graphics cards, the workload is shifted from the CPU to the GPU, allowing for efficient handling of collision detection and response at the vertex level. The integration of depth cubes for collision detection and a mass-spring model for shape preservation enables detailed and realistic grass interactions. Future work aims to extend this approach to other vegetation types and incorporate dynamic game elements for improved visual results.

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GPU- Based Responsive Grass

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  1. GPU-BasedResponsive Grass JensOrthmann, Christof Rezk-Salama, Andreas Kolb

  2. Overview • Motivation • Grass Representation • Collision Handling • Rendering • Results • Future Work

  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. Grass Billboards • Usually: Clumps of grass are approximated by billboards quad with a semi-transparent texture • Crossed billboards produce a more volumetric impression

  5. CPU-BasedPredecision • 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. GPU-BasedCollisionhandling • 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 Recovering Simplification

  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. CollisionDetection • 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. CollisionReaction • 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. Shape Preservation • Spring model preserves the overall shape • Topology information is required • Length constraints correct adjacent vertices

  11. Recovering • Previously collided billboards will regenerate • Interpolation between deformed and undeformed shape • Billboards will be simplified after regeneration undeformed deformed

  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. Rendering • Irradiance information is precomputed for the complete grass layer • During runtime: tri-linear interpolation within the volume results in the irradiance

  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. Results Video

  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. ThankYou • Thank you for your attention

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