P1259229601MSYrD

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Stylistic Rendering of Implicit Models
By Brian Wyvill, Kevin Foster, Pauline
Jepp, Ryan Schmidt, Mario Costa Sousa, Joaquim A.
Jorge.
University of Calgary GraphicsJungle Group
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Problem
Building Shapes Complex objects Smooth curved
volumes Blended objects Branching Collision
detection (Abutting objects) Sharp Junctions
(CSG) Interaction Sketching Stylistic
renderings
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The BlobTree 2005

• Complexity - Hierarchy
• Affine Transformations
• CSG (union, difference, intersection)
• Blend
• Controlled Blend
• Warp (e.g. twist,taper,bend)
• Texture
• Animation Tracks
• Precise contact modelling
• Distance Metrics
• NPR Rendering

Skeletal Implicit primitives
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Control of Blending
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Space Warp
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Complex Models (Natural Phenomana)
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Complex Models (Natural Phenomana)
Murex Cabritii Model Callum Galbraith
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Efficiency

• Rendering slow due to the number of implicit
  function
• evaluations.
• Approaches to speeding up the traversal
• Space Subdivision
• Tree Pruning
• Caching

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Blob Tree With Cache Nodes
Tri-quadratic Vs. Tri-linear interploation
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Variable Resolution
643
323
163

• 1283

• Resolutions are per-component (components are
  tail, body, and left hand)
• Tri-quadratic reconstruction is used for value
  and gradient
• (smoother surface at low resolution)

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Non-Photorealistic Rendering

• Motivation
• Create natural science illustrations
• Art
• Improve rendering time for Implicit Surfaces

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Pen and ink
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Related work

• David Bremmer and John Hughes 98
• Use a raytracer paradigm to create short strokes
  on surface and to trace strokes around contours
• Few rays are used to increase speed
• Integration methods produce good results but are
  expensive

• Gershon Elber 98, 99
• Uses particles distributed on the surface to
  create strokes
• Uses principal directions for stroke direction
• Transparency

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The system
Stylise strokes
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Initialise Particles On Surface

• Particles are initialised on the surface
• partitioned by voxelisation
• distributed by attraction / repulsion.

Fp Rp Attraction repulsion particles within
a voxel attraction along gradient.
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Tracking The Silhouette
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Create strokes from interior particles

• We create small marks following the contour,
  principal directions and arbitrary
  user-controlled directions.
• Vary the width, length and intensity of these
  small strokes on curvature, slope, distance and
  lighting information.

Stroke direction and intensity by contour
Stroke direction by contour, intensity by contour
and lights
Stroke direction by principal direction of
curvature, intensity by light direction.Note
contour strokes.
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Create strokes on CSG regions
CSG Strokes
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CSG Strokes Finding the discontinuity
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CSG Strokes Finding the discontinuity
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CSG Strokes Finding the discontinuity
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CSG Strokes Finding the discontinuity
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CSG Strokes Finding the discontinuity
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CSG Strokes Finding the discontinuity
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm the
racetrack problem
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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CSG Strokes The dual tracking algorithm
maintain straddling
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Finding Discontinuities

• It is desirable to show shape features such as
  CSG junctions that are not on a silhouette. We
  use the difference in gradient criteria to detect
  a feature then track using two particles
• Particles wander on surface if either side of the
  discontinuity (?a - ?b)gt? finds a1 and b1
• 2. Tangent planes through a and b and ?ax?b
  intersect to give first guess, p. Iterate to
  surface.

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Dual Particle Tracking Algorithm
1. Increment a step in direction d1 ?a X ?b 2.
If b2 is inside then scale d1 to allow for the
inside track. 3. if the points bracket the
feature then continue else It could be that one
of the particles crosses the surface (blue
particle at step 3). Take the vector v3 b3
(b2 - a2) take the step and iterate to surface.
a3
b3
v3
a2
b2
d1
a1
b1
Particles a,b positions after 3 steps
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Speleothem
grown using BlobTree simulation hooks,
rendered by ray tracing and NPR techniques.
(Callum Galbraith)
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Sketch Based Interface and Caching
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Sample BlobTree Movies
Wedding Invitation
Wedding Invitation Out-Take