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Energy-Brushes: Interactive Tools for Illustrating Stylized Elemental Dynamics

Jun Xing, Rubaiat Habib Kazi, Tovi Grossman, Li-Yi Wei, Joe Stam, George Fitzmaurice

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Introduction

  • Dynamic effect animation:
    • Waves
    • Splashes
    • Fire
    • Smoke
    • etc.

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Introduction

  • Dynamic effect animation:
    • Key-frames
      • Full artistic control and expression
      • Require significant expertise and manual labor
    • Simulation
      • Realistic animation
      • Hard to control and understand

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Introduction

  • Sketch-based user interface
    • Focus on active and primary character animations
      • Result motion are typically kinetic (velocity is static over time)
      • Easy to specify and control
    • Elemental dynamics are passive and secondary visual effect
      • Underlying forces and motion change over time
      • Challenging to control

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Introduction

  • Dynamic effect animation:
    • Energy strokes

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Goal

  • Elemental dynamics animation framework
    • Energy brushes to design elemental dynamics
    • Approximate and automate traditional hand-drawn animation pratices
    • Balances between key-framing and simulation �approach

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System Implementation

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Stroke

  • Stroke
    • Sample each stroke with constant distance �(6-pixels)
    • Delaunay triangulation

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Delaunay triangulation

  • Delaunay triangulation
    • Try to maximize the angles in triangulation
    • Tend to avoid sliver triangles

Gustavo - Delaunay triangulation does not minimize edge length.gif - Creative Commons Attribution-Share Alike 3.0 Unported

https://commons.wikimedia.org/wiki/File:Delaunay_triangulation_does_not_minimize_edge_length.gif

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Flow Particles

  • Flow
    • Each flow has several particles
    • Particles will move over time

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Flow Particles

  • Flow Particles
    • Each particles has distinct properties
    • If a stroke vertex is in the range of the flow particle, it will have an individual influence value

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Flow Particles

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Flow Particles

  • Influence
  • Distance

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Flow Particles

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Different Flow Particles

  • Flow Particles
    • Wind
    • Swirl
    • Smoke
    • Custom

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Different Flow Particles

  • Flow Particles
    • Wind

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Different Flow Particles

  • Flow Particles
    • Swirl

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Different Flow Particles

  • Flow Particles
    • Smoke

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Different Flow Particles

  • Custom Particles

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Motion Script

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Constraints

  • Anchor Constraint
    • Fixed location

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Constraints

  • Stretch Constraint
    • Has a force to move toward or away if the length is stretched or squashed

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Constraints

  • Rigidity Constraint
    • As-rigid-as-possible deformation method

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Constraints

  • Rigidity Constraint
    • Treat the sample on sharp turns or stroke ends as control points
    • The rest are free points

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Constraints

  • Rigidity Constraint
    • First evolved by the flow particles
    • Then free samples are deformed by rigidity

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Constraints

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Resampling

  • Resampling
    • Distance between adjacent samples may become non-uniform after deformation
    • Resample the stroke after deformation

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Resampling

  • Resampling
    • Anchor samples are not resampled as they remain unchanged

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Resampling

  • Resampling
    • Rigidity segments are not resampled since its based on as-rigid-as-possible approach

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Resampling

  • Resampling
    • Free samples get resample according to the original sample distance.
    • Adjust stretch constraints by distance

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User Interface

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User Interface

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Limitation and Future Work

  • Color and texture
    • Does not support rigid object animation
    • Does not support topology or color changes
    • Severe distortion could poorly map the texture
      • Increase the stretch constraint
      • Use sufficiently smooth textures

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Limitation and Future Work

  • Dynamic effect
    • Different flow effect may conflict and cancel each other
      • Decompose complex effect into layers and hierarchies
    • Reproducing a given effect accurately can be difficult
      • Resulting animations are first-order effects of the underlying energy fields

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Limitation and Future Work

  • Elemental Dynamics Design
    • Didn’t apply static forces that does not move or change over time
      • Gravity
    • Possibility of 3D environment application.

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Video