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Level of Detail. CS184-Sp05 Section. Level of Detail. Basic Idea Use simpler versions of an object as it makes less of a contribution Generation How to make different LODs Selection Chooses LOD based on some criteria Switching Change from one LOD to another. Switching. Popping problem

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level of detail

Level of Detail

CS184-Sp05 Section

level of detail1
Level of Detail
  • Basic Idea
    • Use simpler versions of an object as it makes less of a contribution
  • Generation
    • How to make different LODs
  • Selection
    • Chooses LOD based on some criteria
  • Switching
    • Change from one LOD to another
switching
Switching
  • Popping problem
  • Discrete Geometry LODs
    • No blending. Bad popping.
switching1
Switching
  • Blend LODs
    • Render LOD1 opaquely first, then LOD2 w/ increasing alpha val.
    • High overhead during transitions.
switching2
Switching
  • Alpha LODs
    • Only 1 LOD per object.
    • As metric for selection increases, transparency is increased.
    • No popping.
    • When object completely disappears, don’t need to render it at all.
      • Only at this point is speedup attained.
switching3
Switching
  • CLODs (Continuous Levels of Detail)
    • Huge set of LODs
      • Each level has 1 edge collapse (2 fewer polygons)
        • Edge collapse – vertex joined with another
        • Keep track of edge collapses to reverse (vertex split)
    • Can animate edge collapse for smooth transition
    • Problems:
      • Not all models look good.
      • Have to go through all prior edge collapses to get to a particular LOD
switching4
Switching
  • Geomorph LODs
    • Interpolate between 2 LODs
      • Remember vertex connectivity between levels
    • E.g., animating the edge collapse in CLODs would be a geomorph
progressive mesh

v6

v1

v1

v7

v4

v4

v2

v3

v3

v3

v5

v5

Progressive Mesh
  • CLOD as described earlier
    • Order to collapse edges is determined by some absolute cost metric
      • Always collapse in same order
    • Store edge, adjacent faces, and vertices of adjacent faces
      • When an edge collapses, the 2 endpoints disappear and a NEW vertex is placed somewhere (e.g. along the old edge).
view dependent progressive mesh
View-Dependent Progressive Mesh
  • View-dependent progressive mesh
    • Order in which we want to collapse edges is based on view
      • Will collapse in different orders for different views
      • Can’t just store in a list like w/ CLODs
basic alg
Basic Alg.
  • First create the view-independent progressive mesh
  • At run-time, create a forest of LOD info
    • Start w/ the coarsest mesh
    • Try to split “best” vertex given view-dependent metric
      • If that split depends on splitting another vertex first, do that
basic alg1

v6

v1

v1

v7

v4

v4

v2

v3

v3

v3

v5

v5

Basic Alg.

1) Create PM: Mn <- Mn-1 <- … M0

2) Create forest

M0

v1

v2

v3

Say our v.d. metric says to split v1 first.

Can we do that? (Hint: No)

billboards
Billboards
  • So far, we’ve been working with meshes
  • Billboards
    • Render an image onto a polygon facing the viewer OR have several “cross-billboards”
    • Used in video games
    • Useful for simulating “special effects”
      • Lens flares
  • Switching between different LOD textures will create creases
    • Fix problem by using mipmaps
lod selection
LOD Selection
  • Back to meshes
  • Very application oriented
    • Range-Based
    • Projected-Area Based
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