AnimationinVideoGames.ppt

Animation in Video Games presented by Jason Gregory Agenda The Goal of Game Animation Old School Animation Skeletons and Skins How Skinning Works (Graphically) The Math of Skinning Animation: Bringing a Character to Life Blending and other Advanced Topics The Goal of Game Animation Our goal is simple: To produce realistic looking animated characters in our games! Old School Animation The very first animated characters were 2D sprites. Just like traditional cel animation or flip books. Old School Animation (2) Old School Animation (3) When we moved to 3D, our first animated characters were “jointed.” Each limb or part of a limb is a separate rigid object. Problem: Interpenetration at joints! Old School Animation (4) Skeletons and Skins Modern approach is called “skinning.” Basic idea: Create a jointed skeleton. Attach the skin to the skeleton. Move skeleton around – skin follows it. Skin is a 3D model made out of triangles. Skeleton is invisible – only the skin is seen by the player. Skeletons and Skins (2) Skeletons and Skins (3) Each vertex of each triangle is attached to one or more bones. We use weights to define bones’ influences. Weights at a joint must always add up to 1. Skeletons and Skins (4) Skeletons and Skins (5) Skeletons have two kinds of poses: Bind Pose: The skeleton’s pose when the skin was first attached. Current Pose: Any other pose of the skeleton; usually a frame of an animation. The bind pose is like a “home base” for the character’s skeleton. If you drew the mesh without its skeleton, it would appear in its bind pose. Skeletons and Skins (6) Bind Pose How Skinning Works Consider a single vertex (v) skinned to the joint J1. The skeleton is in bind pose: How Skinning Works (2) We want to find the vertex’s new location (v) in the current pose. How Skinning Works (3) The basic idea is to transform the vertex: from model space into joint space The coordinates of the vertex are invariant in joint space! So, we can move the joint around all we wa