Digital Media Dr. Jim Rowan ITEC 2110 Vector Graphics II

Vector Graphics 3-D... 3 dimensions x, y and z x & y form the ground plane z is the height

3D 3D shapes (objects) are defined by their surfaces Made even more complicated by the fact that a 3D object inside the computer must be translated into 2D to be rendered… This results in the need to –specify the viewpoint, a camera –specify the lighting

3D But… having to specify the camera and the lighting buys you one huge advantage that you do not get when doing 2D rendering automatically generates all of shadows BUT… rendering is extremely computationally expensive (demanding, time consuming)

3-D: even more complexity lighting has different characteristics and must be specified –natural or artificial –spot or flood –color –multiple sources –reflections off other objects in the scene atmosphere must be intentionally included surface texture must be specified

ent_group_2_Vector_Graphics_3D issues of focus/atmosphere examples from Sintel

Managing Complexity

Structural hierarchy Things in the real world are compositions of smaller things Things in the 3-D graphics world are also compositions of smaller things Hierarchical structure is an excellent way of coping with complexity Also seen in object-oriented programming like Java and Squeak!

3D Models

So… how do you build a model inside a computer when you can’t touch it? Constructive Solid Geometry Free Form: Extrusion Meat balls Procedural modeling

3D models Constructive solid geometry –building things from known shapes –uses geometric solids: cube, cylinder, sphere and pyramid –objects build by squishing and stretching those objects –objects joined using union, intersection and difference

Intersection

Difference

Union or just 2 objects?

Free Form Building things one side at a time Uses an object’s surface (it’s boundary with the world) to define it Build surfaces from flat polygons or curved patches –flat polygons are easier to render and therefore frequently used in games where computational power is limited Results in an object drawn as a “mesh” Can be done using Bezier surface patch but they have 16 control points! More tractable (do-able) patch uses a surface called a non-rational B-spline

Free Form: Extrusion Building things using a playdoh factory Draw a 2 dimensional shape through space along a line The line can be straight or curved

Meat balls Reacts like soft objects rather than hard, solid ones Think of the objects as having surface tension Kinda like an uncooked meatball, press two of them together and they “squish”

Procedural modeling Best known is based on Fractals –Fractals –exhibit the same structure at all levels of detail –aka “self similar” –used to model natural objects – Particle systems... many particles, few controls Physics... distribution of mass, elasticity, optical properties, laws of motion

3D Rendering Rendering engine handles the complexity Wire frames are used to preview objects and their position –can’t tell which surface is closer to us and which surface is hidden To save computation time, hidden surfaces are removed before rendering –Why render what can’t be seen?

3D rendering Lighting –Added to scene much like an object –spot light, point source, floodlight... –position and intensity Direct relationship between rendering quality and computational burden

3-D rendering Shading... how light reacts with surface –Based roughly on physics but modified by heuristics (rules derived from experience) –Examples ===> Texture mapping –An image is mathematically wrapped around the object

3-D rendering Light reflecting off objects of one color affect the color and lighting of surrounding objects –Ray tracing Complex... must be repeated for pixel in the image... photo-realistic results –Wayne Wooton Pixar –Radiosity

Questions?