Hardware Instancing for Real-time Realistic Forest Rendering

彬彬

1 Introduction

Real-time rendering of vegetation is important in many applications,

such as video games, internet graphics applications, landscape

design and visualization. However, the visualization of large-scale

forests has always been a challenge not only due to the high geometric

complexity but also due to the small batch problem. Moreover,

generating real-time shadows for forests will heavily increase the

burden. The batch problem is caused by a large number of graphics

API draw calls launched in every frame. Normally, rendering a tree

model requires at least one graphics API draw call. As a forest usually

consists of thousands of trees and the graphics API invocation

is a relatively high cost for CPU, the large-scale forest rendering is

often CPU bound.

As the computational capabilities of GPU are growing much faster

than that of CPU, more and more methods focus on minimizing

the number of driver invocations to solve the CPU bound problem.

Most methods such as [C***cci and Studios 2005] work like this: in

each frame, they first update all geometry instances in the view ***stum

and then put the updated data into several vertex buffer objects

(VBOs) and finally render the VBOs in a few draw calls. These

methods still need CPU interventions such as culling instances against

the view ***stum and determining appropriate LOD models.

The method of [Shopf et al. 2008] uses geometry shaders to perform

culling and dynamic LOD selecting on GPU. However, it is not

intended for modern graphics hardware and it needs many rendering

passes to separate LODs. The method of [Decaudin and Neyret

2004] utilizes no periodic tiles of volumetric textures to render vast

and dense forests by using the texturing power of graphic hardware.

It relies on LODs and a GPU-friendly s***cture to produce dense

forests corresponding to continuous non-repetitive fields. However,

e-mail:xiaopeng.zhang@ia.ac.cn

walking through into these forests is not available.

We present a novel framework which renders a large-scale forest

scene containing over one million highly detailed trees in real-time

with real-time shadowing effects. The framework is well integrated

with GPU-based dynamic geometry LOD [R´akos 2010] and

parallel-split shadow mapping (psSMs) [Zhang et al. 2006]. Our

method overcomes the limitation in [R´akos 2010] that separates instances

into only a limited number of LOD levels. By taking advantage

of the latest functionalities introduced in OpenGL 4, the

number of driver invocations is dramatically reduced. Culling and

LOD determining are entirely implemented on GPU without breaking

the drawing batches by complicated and expensive CPU-based

methods. This method is straightforward and does not need any extra

scene management algorithm. Occlusion culling is beyond the

scope of this paper

彬彬

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