Graphics Interface 2009

The-Kiet LuKok-Lim Low

Jianmin Zheng

1

Rendering high-detail surface (>100M points) is inefficient when vertices are independently processed one-by-one in real-time• Redundant processing

Occlusion LOD # of pixels vs. # of vertices

1024x1024 pixels vs. 368 millions points Memory size

1 vertex requires > 6 bytes (un-compressed) St. Mathew (368 M) > 2Gbs

Simplification – slow• Requires surface reconstruction first

2

Hybrid approach• Object-space and screen-space solution• Display 3D models by per-pixel ray-casting a

set of 2D height fields (displacement mapping)

3

4

1) 2D Height Field Construction• Decompose points using octree• Generate height field maps• Generate height field bounding boxes

2) Height Field Rendering• Rasterize bounding box.• For each fragment rasterized:

Transform viewing ray to height field map coordinate space

Ray-casting — compute ray-surface intersection.

5

Decompose points using an octree so that each cell contains points forming a valid height field

6

Using PCA to determine Height Field domain plane. Height Field map is generated as displaced distance between the Surface and the PCA plane.

7

The faces of the octree cells that bounds the height filed surface are added into Vertex buffer with appropriately assigned texture coordinates.

8

Each fragment, the viewing ray is transformed from world coordinate frame into locals of the corresponding 2D height map.

9

We compute intersection by marching along the viewing ray from initial location

to the closet point above the Height Field map.

Culling Test: A simple Texture coordinate check to ensure the ray indeed intersects the current height map – not the neigh borings.

Xi = Xi-1 + v x ∆h

v

10

Hybrid approach• Optimize

Automatic Screen-space occlusion culling Back Face culling Early Z-culling

Memory consumption 6 bytes vertex vs. 8-bit depth buffer Texture compression

• Limitation Performance subjects to screen resolution

11

12

A main advantage of our method is its simplicity in dealing with  silhouettes  correctly.

13

1 iterations 4 iterations 8 iterations

14

15

16

17

Comparison: point-based Mar2007 : 6060M per second – our method results with 368M368M (St. Mathew) with 12 Fps on GeForce Go 7900 GPU - Intel Core 2 Duo 2.4 GHz..

18

We have presented a new approach for fast visualization of highly detail 3D models by decomposition 3D model into Height Fields and render these Height Fields using image-space ray-casting algorithm that offers significant performance improvement compared to previous point-based approach.

Our current limitation is that it is not efficient for flat and smooth surfaces as well as not applicable for dynamic or deformable surfaces – our current research topic.

19