Level of Detail

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# Level of Detail - PowerPoint PPT Presentation

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

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
• Discrete Geometry LODs
Switching
• Blend LODs
• Render LOD1 opaquely first, then LOD2 w/ increasing alpha val.
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.
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
Switching
• Geomorph LODs
• Interpolate between 2 LODs
• Remember vertex connectivity between levels
• E.g., animating the edge collapse in CLODs would be a geomorph

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
• 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
• 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.
• 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

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
• 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
• Back to meshes
• Very application oriented
• Range-Based
• Projected-Area Based