CS361Week 11 - Wednesday

Last time

Image based effects Skyboxes Lightfields Sprites

Billboards Particle systems

Questions?

Project 3

Impostors An impostor is a billboard created on the fly by

rendering a complex object to a texture Then, the impostor can be rendered more cheaply This technique should be used to speed up the

rendering of far away objects The resolution of the texture should be at least:

tan(fov/2) distance2size objectresolution screen

Displacement techniques An impostor that also has a depth map

is called a depth sprite This depth information can be used to

make a billboard that intersects with real world objects realistically The depth in the image can be compared

against the z-buffer Another technique is to use the depth

information to procedurally deform the billboard

Duck Video

Billboard clouds Impostors have to be recomputed for different

viewing angles Certain kinds of models (trees are a great example)

can be approximated by a cloud of billboards Finding a visually realistic set of cutouts is one part

of the problem The rendering overhead of overdrawing is another

Billboards may need to be sorted if transparency effects are important

Image processing

Image processing takes an input image and manipulates it Blurring Edge detection Any number of amazing filters

Much of this can be done on the GPU

And needs to be (blurring shadows) Photoshop and other programs are GPU

accelerated these days

Filtering kernels From Project 1, you

guys know all about convolution filtering kernels

I just wanted to point out that some kernels are separable Rows and columns can be

done separately A separable m x m

kernel can be run in 2mn2 time instead of m2n2 time

Color correction

Color correction takes an existing image and converts each of its colors to some other color Important in photo and movie processing Special effects Time of day effects

Tone mapping Tone mapping takes a

wide range of luminances and maps them to the limited range of the computer's screen

To properly simulate the relative luminances Some bright areas are

made extremely bright Some dark areas are

made extremely dark We can look for the

brightest pixel and scale on that basis

Lens flare and bloom Lens flare is an effect caused by bright light hitting

the crystalline structure of a camera lens Actually happens less and less now that camera technology

has improved They can be rendered with textures

The bloom effect is where bright areas spill over into other areas To render, take bright objects, blur them, then layer over

the original scene

Fiat LuxDirected by Paul DebevecThe greatest graphics technology of… 1999

Depth of field In photography, some

things are in focus and some things (either too near or too far) are blurry

When desired, this effect can be achieved by rendering the image in a range of blurred states and then interpolating between them based on z-value

Motion blur Fast moving objects exhibit

motion blur in films It doesn't often happen in real life We have come to expect it,

nevertheless The effect can be reproduced by

keeping a buffer of previously rendered frames, adding the latest frame and subtracting the first frame

Other techniques can be used to do various kinds of selective, directional blurring

Fog Fog effects can be used to give atmosphere or

cue depth Fog is usually based on distance (z-buffer or

true distance) from the viewer Different equations determine the effect (linear

or exponential) of the fog

DirectX fog The BasicEffect makes fog easy with the

following members FogEnabled Whether fog is on or off FogColor Color of the fog FogStart Distance (in world space) where fogstarts to appear FogEnd Distance (in world space) where fogcovers everything

It's not hard to write shader code that interpolates between fog color and regular color based on distance

Quiz

Upcoming

Next time…

Polygonal techniques Tessellation and triangulation

Triangle strips, fans, and meshes Simplification

Static Dynamic View-dependent

Reminders

Finish Project 3 Due tomorrow before midnight

Exam 2 is next Friday in class Next Wednesday will be review Review chapters 5 – 10