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Mastering Level of Detail: Techniques & Strategies for Optimal 3D Modeling Efficiency

Explore the concept of Level of Detail (LOD) in 3D modeling, including LOD generation, selection, switching techniques, and common problems like popping. Learn about LOD blending, CLODs, Geomorph LODs, Progressive Mesh, View-Dependent Progressive Mesh, Basic Alg, and use of Billboards. Understand LOD Selection methods for enhanced 3D rendering efficiency tailored to your application needs.

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Mastering Level of Detail: Techniques & Strategies for Optimal 3D Modeling Efficiency

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  1. Level of Detail CS184-Sp05 Section

  2. 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

  3. Switching • Popping problem • Discrete Geometry LODs • No blending. Bad popping.

  4. Switching • Blend LODs • Render LOD1 opaquely first, then LOD2 w/ increasing alpha val. • High overhead during transitions.

  5. 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.

  6. 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 • …

  7. Switching • Geomorph LODs • Interpolate between 2 LODs • Remember vertex connectivity between levels • E.g., animating the edge collapse in CLODs would be a geomorph

  8. 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).

  9. 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

  10. 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

  11. 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)

  12. 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

  13. LOD Selection • Back to meshes • Very application oriented • Range-Based • Projected-Area Based

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