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GPU- Based Responsive Grass. Jens Orthmann, Christof Rezk-Salama, Andreas Kolb. Overview. Motivation Grass Representation Collision Handling Rendering Results Future Work. Motivation. Physically correct reacting environment improves immersion for players
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GPU-BasedResponsive Grass JensOrthmann, Christof Rezk-Salama, Andreas Kolb
Overview • Motivation • Grass Representation • Collision Handling • Rendering • Results • Future Work
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
Grass Billboards • Usually: Clumps of grass are approximated by billboards quad with a semi-transparent texture • Crossed billboards produce a more volumetric impression
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
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
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
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
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
Shape Preservation • Spring model preserves the overall shape • Topology information is required • Length constraints correct adjacent vertices
Recovering • Previously collided billboards will regenerate • Interpolation between deformed and undeformed shape • Billboards will be simplified after regeneration undeformed deformed
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
Rendering • Irradiance information is precomputed for the complete grass layer • During runtime: tri-linear interpolation within the volume results in the irradiance
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
Results Video
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
ThankYou • Thank you for your attention