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CS361 Week 11 - Wednesday

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Page 1: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

CS361Week 11 - Wednesday

Page 2: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Last time

Image based effects Skyboxes Lightfields Sprites

Billboards Particle systems

Page 3: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Questions?

Page 4: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Project 3

Page 5: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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 object

resolution screen

Page 6: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 7: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Duck Video

Page 8: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 9: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 10: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 11: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 12: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 13: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 14: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Fiat LuxDirected by Paul DebevecThe greatest graphics technology of… 1999

Page 15: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 16: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 17: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 18: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

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

Page 19: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Quiz

Page 20: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Upcoming

Page 21: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Next time…

Polygonal techniques Tessellation and triangulation

Triangle strips, fans, and meshes Simplification

Static Dynamic View-dependent

Page 22: Week 11 - Wednesday.  Image based effects  Skyboxes  Lightfields  Sprites  Billboards  Particle systems

Reminders

Finish Project 3 Due tomorrow before midnight

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