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Understanding 3D Models and Animations: Types, Usage, and Animation Techniques

A 3D model is a collection of data that represents objects in a 3D world, encapsulating vertices, normals, and textures. These models can be categorized into static geometry, screen-aligned geometry (billboards), and animated geometry. Static models depict unchanging objects like walls and statues, while billboards are 2D planes always aligned with the camera. Animated geometry includes character models and fluid simulations, utilizing vertex and bone animation techniques. Understanding these categories and animation methods is essential for effective 3D rendering.

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Understanding 3D Models and Animations: Types, Usage, and Animation Techniques

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Presentation Transcript

  1. Topics: Models & Animations • 3D Models • Animations

  2. What is a 3D Model? • A 3D Model is a bunch of data (vertices, normals, texture coordinates, color etc) which usually represents an object in the 3D world

  3. Usage of models • 3D models can be used to • Render an instance or entity in the scene • Represent collision data (for trigger points, bounding volumes etc)

  4. Categories of a 3D Model • A model can be divided into several categories • Static Geometry • Screen Aligned Geometry (Billboard) • Animated Geometry

  5. Static Geometry • Are used for objects that do not animate, e.g. statues, walls, doors. • Data can be represented in world space instead of local model space to avoid local->world transformation • Static lighting can be baked into textures • Common file formats are .X, .OBJ, .3DS

  6. Screen Aligned Geometry • A 2D plane which is always aligned with the camera, commonly known as billboards • Can animate texture coordinates (UV), blend and render several billboards together, resize at runtime • Can be used for particles (explosions, fire etc), clouds, skybox, lens flare, foliage, UI, shadow maps

  7. Billboard Clouds Taken from Real Time Cloud Rendering by Mark J Harris

  8. Animated Geometry • Can be used for characters, morphing objects, water, cloth, fluid • Animation data is divided into two types –vertex and bone

  9. Vertex Animation • Vertex animation or morphing, is moving the positions of each vertex every frame. • Disadvantage is huge data size as each vertex must store vertex positions for each frame • Used in older engines like Quake 2, .md2 format

  10. Vertex Animation -Water Taken from “Inexpensive Underwater Caustics Using Cg” –Gamasutra2003

  11. Vertex Animation -Cloth Taken from Interactive Cloth Sim-Nvidia GDC 2001

  12. Bone Animation -Skinning • Instead of storing the positions of each vertex, we store a bone hierarchy and animate the bone. Vertices are calculated and blended at runtime based on the bone they are affected by. These vertices are called a skin • Skinning is slower since we need to calculate vertex positions. We trade memory with speed.

  13. Skinning 􀂄Taken from Flipcode.com

  14. Skinning • One problem is skinning is the vertex movement is rigid • Require vertex blending when each vertex is affected by multiple bones. Each vertex stores a weight percentage per bone and is usually limited to 4 bones (hardware limit).

  15. Skinning

  16. Animation Data • What do you need to store? • 3D Mesh • Textures • Frame • What else?

  17. KeyFrame • Animation data is stored per keyframe instead of every frame. A keyframe is a pose in the animation cycle and stores the position and orientation of every bone in that pose. • Two kind of keyframes–forward and inverse kinematics

  18. Forward Kinematics • The position and orientation of each bone is stored per keyframe is stored and interpolation (linear, cubic etc) is used to calculate the vertices between each keyframe. • This is just simple bone animation

  19. Inverse kinematics • Given a final position, how should my bone bend so I can reach it? • No animation data is stored as the bone animation data is calculated at runtime based on desired position

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