slide1
Download
Skip this Video
Download Presentation
Graftal textures

Loading in 2 Seconds...

play fullscreen
1 / 24

Graftal textures - PowerPoint PPT Presentation


  • 101 Views
  • Uploaded on

Art-based Rendering with Continuous Levels of Detail Lee Markosian, Barb Meier, Michael Kowalski, Loring Holden, J. D. Northrup, and John Hughes. Graftal textures. “Art-based Rendering of Fur, Grass and Trees,”. by Kowalski, Markosian, Northrup, Bourdev, Barzel, Holden, and Hughes.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Graftal textures' - keona


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Art-based Rendering with Continuous Levels of DetailLee Markosian, Barb Meier, Michael Kowalski, Loring Holden, J. D. Northrup, and John Hughes.

graftal textures
Graftal textures

“Art-based Rendering of Fur, Grass and Trees,”

by Kowalski, Markosian, Northrup, Bourdev, Barzel, Holden, and Hughes.

Siggraph 99.

problems
Problems
  • Coherence
    • excessive introduction/elimination of graftals
    • popping
  • Graftal textures defined in code
    • hard to edit
    • how to extend with UI?
a new framework
A new framework
  • Drawing primitives
    • triangle strips (or fans)
    • Strokes
  • Graftals
tufts
Tufts

A tuft is a hierarchical collection of graftals

basic graftals
Basic graftals
  • Collection of drawing primitives
  • Canonical vertices
  • Local coordinate frame
    • Affine map transforms canonical vertices to the local frame
the local frame

local frame

x

canonical space

The local frame
  • Base position (e.g. on surface)
  • y´(e.g. surface normal)
  • x´(e.g. cross product of y´ and view vector)

M

y

placement and duplication
Placement and duplication
  • Designer creates a few “example graftals”
  • Duplicates of these are distributed over surfaces (“static” placement)
    • explicit distribution
    • procedural distribution
  • In duplication, graftal parameters can be varied randomly within specified range of values
level of detail lod
Level of detail (LOD)
  • Each graftal computes a desired LOD
  • Then draws its primitives accordingly
    • each primitive has an associated threshold value
    • it’s drawn if the computed LOD exceeds the threshold
computing lod
Computing LOD
  • Desired LOD is quantified by value   0
  •  computed from 3 values:
    •  (depends on apparent size)
    •  (depends on orientation)
    •  (depends on elapsed time since graftal’s introduction)
slide13
is the ratio of the graftal’s current screen size to its “expected” screen size

 = .7

 = 1.4

 = 1

computing
Computing 
  •  lies in the range [0, 1]
  • We use  to suppress the final LOD value  in some regions
  • E.g.,  = 1 - |v · n|
tufts1
Tufts

Graftals in a tuft are grouped into levels

level 2

level 1

tufts cont d
Tufts, cont’d
  • Each level i has an associated value i
  • Graftals at level i are drawn if   i
  • Actually, we use hysterisis to choose the current active level
    • discourages level transitions
computing1
Computing 
  •  is used to smoothly introduce graftals when a given level becomes active
  • Each level has an associated “transition time,” e.g. 0.8 seconds
  • Say the level became active 0.6 seconds ago
  • Then  = 0.6 / 0.8 = 0.75
using
Using 
  •  can be used to animate or morph a graftal’s shape
    • we’ve done this by scaling and rotating graftals
  • It can also affect the computed LOD 
    • e.g.  = 
conclusions
Conclusions
  • New framework provides more flexibility
    • range of graftal looks / behaviors
    • editing text files easier than writing code
  • Much better temporal coherence
conclusions cont d
Conclusions, cont’d
  • New approach is slower for complex scenes
    • night scene takes about 1 fps
    • work is expended on off-screen graftals
    • should use culling
  • Handling of LOD is too inflexible
    • levels have pre-assigned order
future work
Future work
  • Generalize handling of LOD
  • UI for directly sketching graftals
  • UI for sketching other stroke-based textures by example
  • UI for sketching free-form shapes
    • continuing work on “skin” (Siggraph 99)
  • Integrating these into a single system
ad