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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

• 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

• Popping problem

• Discrete Geometry LODs

• Blend LODs

• Render LOD1 opaquely first, then LOD2 w/ increasing alpha val.

• 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.

• 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

• Geomorph LODs

• Interpolate between 2 LODs

• Remember vertex connectivity between levels

• E.g., animating the edge collapse in CLODs would be a geomorph

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

• 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

• 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

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)

• 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

• Back to meshes

• Very application oriented

• Range-Based

• Projected-Area Based