Procedural terrain on the GPU

Chalmers University of TechnologyAdvanced computer graphics – DAT205

David SundeliusAdam Scott

Introduction

• Generating terrain is a task fitted well for parallelization and thus for the GPU

• A technique to generate terrain, with textures and lighting during runtime.

• Divides the world into cubic blocks containing voxels

Agenda

• Overview• Density function and noise generation• Marching cubes algorithm• Texturing, shading and lighting• Demo• Questions

Terrain generation overview

• Divide environment in blocks of voxels• Parallelize block calculation by using pixelshaders• Use a density function to create the basic environment• Apply noise to the generated density function• Use the marching cubes algorithm to generate geometry• Add textures and texture coordinates• Render scene

Density function

• Function used to create the basic environment

• A three dimensional function

• Positive and negative values

• float density = -1;• float density = -ws.y;• float density = rad – length(ws- float3(0,rad,0));

Noise generation

• Generate some noise 3d texture repeating• Modify the density function with random sampling from our

noise texture• Use interpolation to warp the area• Able to create a hard floor or flat areas, just clamp the density

function• Possibility to use hand made textures• Generate cave structure

Marching cubes - Blocks

• March through voxels in blocks

• For each voxel we create an array with information of corners from the density function

Marching cubes – Lookup tables

• Lookup constructed array

• Pregenereted lookuptables

Marching cubes - geometry

• Geometry shader

• Calculate position of vertex

• Calculate normal

• Three different methods to generate blocks

Block generation method 1

• 1. Fill volume

• 2. Generate vertices

• The slowest method

Block generation method 2

• 1. Fill density volume

• 2. Lightweight marker point

• 3. Generate vertices

Block generation method 3

• 1. Fill volume

• 2. List non-empty cells

• 3. List vertices to generate

• 4. Generate vertices

• 5. Splat vertices

• 6. Make triangles

Lighting and ambient occlusion

• Easy to implement

• Calculating normals

• Ray casting

• Long/short rays

Premade textures

• Pros and cons

• Loading textures (such as photographs)

• Triplanar texturing – project on axis with least distorted normal

Generating textures

• Generating textures

• Marble textures

Pros and cons

• Requires a lot of memory on the GPU• Can compromize valitity of data (not exact), ambiguity in model • Can have holes

• Fast way to generate procedural environments• Easy and fast to manipulate environment• High resolution (easy to extend use to LoD)

Applications

• Level of detail• Collisions• Lighting

• Other use: create 3d models from sampling i.e. MRI

Demonstration

• Video

Further research

• http://undergraduate.csse.uwa.edu.au/units/CITS4241/Project/references/Lorensen-Cline-brief.pdf

• http://code-freeze.blogspot.se/2012/04/rebuilding-world-one-iteration-at-time.html

• The CD to GPU gems 3 – Interactive demo

Questions

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