Research And Implementation On Large Scale Grassland Capturing,rendering And Simulation

Grass is very import element of nature and it is indispensible in many 3D scenes.Grass modeling,rendering as well as simulation are wildly used in many 3D applications.Moreover it is the grass rendering and simulation quality that determines the overall impressions of the whole virtual scene.There are few methods that are designed to reconstruct grass blade models.In former works about grass rendering and simulation,manually designed models are used for geometrical representation of grass blades.However it is difficult for those methods to accurately reconstruct blade shapes.Besides,there are so many grass types in natural world,obviously it is a better idea to recontruct blade shape automatically rather than manually.In order to improve system performance,some former works use billboard to represent grass blades.Nevertheless billboard-based methods do not always achieve satisfactory rendering results.A cluster of blades may map to the same billboard,which limits the movement of those grass blades.As for simulation,it is not blade but billborad that interacts with other objects.As a result it is not physically-real for virtual scenes.As for other methods that use geometry-based representation for grass blades,only a small amount of grass blades could be simulated at the same time because of high computation complexity.Non-simulated grass blades are represented as billboards or 2D textures.The method in this paper is designed to reconstruct grass blade model,render and simulate large scale grassland.We use color images as well as depth image to reconstruct blade shape,and design a model simplification method according to vertices movement and geometry similarity.This simplification method helps reconstructed model to be used in our rendering and simulation system meanwhile achieving high performance.We come up with a tile-based rendering scheme.At first a grass patch is generated before rendering and every tile is instanced from this grass patch.We expand grass blade in vertex shader to save storage space.Finally we implement a grass simulation system that allows to simulate over one million grass blades with individual collision response.Only those tiles that possibly interact with other objects will be added into simulation quenes.We solve the constraits of collision,such as bending and twisting,to update blade movements.This is a physically-real simulation scheme and compatible with global procedual animations such as wind.Futhermore,level-of-detail is also supported in our system.