OpenGL - Particle System Tutorial - Blending - Point Sprites
Week 11 - Wednesday. Image based effects Skyboxes Lightfields Sprites Billboards Particle...
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Transcript of Week 11 - Wednesday. Image based effects Skyboxes Lightfields Sprites Billboards Particle...
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 object
resolution 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