Text Outline of 3D Concepts Slides - 10 March 2009

3D Concepts - Coordinate Systems
• Coordinates specify points in space
• 3D coordinates commonly use X, Y, & Z
• A vertex is a 'corner' of an object
• Different coordinate systems have different measurement orientations
• 3D objects in isolation are measured in object space
• 3D views are measured in world space
• XNA Game Studio world space is right-handed


3D Models
• Defined by their vertices
• Simple 3D models are called primitives: cylinder, cube, cone, sphere
• Simplified model views often use an axis bug instead of a full axis rendition


3D Shapes
• Defined by their polygons
• Usually triangles are used to define polygons
• 3D shapes are often called meshes
• 3D accelerated graphics cards work best with triangle polygons
• The polygons that make up a shape are called faces
• Faces within a shape that are not viewable are called hidden faces
• Faces on the backside of a shape are called back faces

Displaying 3D Models - Three-step process:
1. Convert to world space
(transformation)
2. Convert to view space
(3D rendering)
3. Convert to screen space
(2D rendering)

Displaying 3D Models - Transformation - 3 main types
• Scaling
• Rotating
• Translating

Displaying 3D Models - Scaling
• Multiply measurements in each axis 
• Apply to all of a shape's vertices
• Scale factors larger than 1 will make object bigger
• Scale factors smaller than 1 will make object smaller
• Scale factors of 0 or less are not applicable

Displaying 3D Models - Rotation
• Each axis is rotated in turn
• Order of rotation matters
• Roll: rotate around longitudinal (Z) axis
• Pitch: rotate around lateral (X) axis
• Yaw: rotate around vertical (Y) axis
• Common convention is roll-pitch-yaw ordering

Displaying 3D Models - Translation
• Moves an object in space
• Vectors are applied to a shape's vertices to translate it
• Shape is not changed
• Shape is not re-oriented


Displaying 3D Models - Rendering
• Process of converting a 3D model of a shape to 2D picture
• Shading
• Mapping
• Graphing


Displaying 3D Models - Rendering
• Flat Shading
• Lambert Shading
• Gouraud Shading
• Phong Shading
• Fake Phong Shading
• Texture Mapping
• Shaders
• Bump Mapping
• Environment Mapping
• Mipmapping
• Scene Graphs

Displaying 3D Models - 3D Audio
• Positioning sound in 3D using stereo
• Balancing left & right & volume control can approximate 3D position of sound


Displaying 3D Models - 3D Programming
• XNA has built-in methods to use
• Scenegraph insertion is not automatic, but is a useful abstraction 
• placing (spawning)
• transforming
• allows us to manually manipulate objects as well
• Real-time scene manipulation


Summary 
• 3D coordinates can be expressed as left-handed or right-handed
• Objects are designed in object space, placed in game world in world space
• Object space may use a different coordinate system than world space, and each uses a different center (zero reference)
• Changing an object's size, orientation, or location is called transforming the object
• Order of transformation matters
• The axis order of rotation matters
• Converting the mathematical description of an object to a visual representation on a screen is called rendering
• Scene graphs contain and organize objects in a world in preparation for rendering and manipulation
• XNA provides many methods for manipulating and moving 3D objects in real time
• 3D Audio effects can be handled in exactly the same way as regular 3D objects