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Презентация на тему Image-based Rendering

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IntroductionSprite, billboard, overview
Image-based RenderingRef: RTRv2 IntroductionSprite, billboard, overview Ridge Racer (Namco) TechniquesSprite:A small image, often used in animated games but also sometimes used See-Thru Textures (aka, cutouts)Test α of transparent part Enable alphatest Definition (Billboard)A textured polygon always rotated to face the viewerTwo kinds:Cylindrical: for AssumptionsFor cylindrical billboards:In OpenGL coordinate systemthe scene is on XZ planeView Up Cylindrical Billboard Spherical billboards Rotate about localY θ = acos (n,pxz) Rotate about localX Where is the camera?For any reason (e.g., cylindrical billboard), you want to Finding Up DirectionSpherical Viewerup Screen/World Aligned BillboardsBillboardsReal spheres Screen-aligned Billboardv: [0,0,1] in eye coord.Transform into world coord.During each frame:Rotate every n into v Billboard Cloud for  Extreme Model Simplification (url) Application: (Quasi-)ImpostorImpostor: render 3D object into texture, in various viewing anglesInstead of Impostor-2Usually textures are stored in a single texture object, to avoid repeated ImpostorsA billboard created on the flyrendering a complex object from the current Impostors (Schaufler)The top of figure 1 shows an object for which an Impostors (cont)Idea:Project the bounding box of the object to determine size of Impostors (cont)Rendering speed depends on the number of pixelsUsage:A few instances of Impostor: texture resolution Impostors RegenerationSchauflerβtex, βtrans, or βsize ≥ βscr Problem of Billboard Coherent Layers (Lengyel and Snyder, 1997)Hand animators use layers to reduce the Chicken Run (80 layers) Depth Sprites (Nailboards) Nailboards (cont) Hierarchical Image CachingUse impostors in a hierarchy for better performancePartition the scene Full-screen BillboardingNot really “billboard” per se; just something that covers the whole
Слайды презентации

Слайд 2 Introduction
Sprite, billboard, overview

IntroductionSprite, billboard, overview

Слайд 3 Ridge Racer (Namco)

Ridge Racer (Namco)

Слайд 4 Techniques
Sprite:
A small image, often used in animated games

TechniquesSprite:A small image, often used in animated games but also sometimes

but also sometimes used as a synonym for icon.
World-aligned

billboards
Cylinderical and spherical
Impostors

Слайд 5 See-Thru Textures (aka, cutouts)
Test α of transparent part

See-Thru Textures (aka, cutouts)Test α of transparent part Enable alphatest


Enable alphatest


Слайд 6 Definition (Billboard)
A textured polygon always rotated to face

Definition (Billboard)A textured polygon always rotated to face the viewerTwo kinds:Cylindrical:

the viewer
Two kinds:
Cylindrical: for cylindrically symmetric objects (e.g., trees)
Spherical:

for spherically symmetric objects (e.g., smoke)

Слайд 7 Assumptions
For cylindrical billboards:
In OpenGL coordinate system
the scene is

AssumptionsFor cylindrical billboards:In OpenGL coordinate systemthe scene is on XZ planeView

on XZ plane
View Up is Y-axis
Viewer need not stay

on XZ plane

Слайд 8 Cylindrical Billboard

Cylindrical Billboard

Слайд 9 Spherical billboards
Rotate about localY
θ = acos

Spherical billboards Rotate about localY θ = acos (n,pxz) Rotate about

(n,pxz)
Rotate about localX
φ = acos (pxz,p)
Watch out

for signs of angles

Слайд 10 Where is the camera?
For any reason (e.g., cylindrical

Where is the camera?For any reason (e.g., cylindrical billboard), you want

billboard), you want to know where camera is, just

remember that the eye coordinate of the camera is always at the origin [facing –Z]




Слайд 11 Finding Up Direction



Spherical Viewer

up

Finding Up DirectionSpherical Viewerup

Слайд 12 Screen/World Aligned Billboards

Billboards

Real spheres

Screen/World Aligned BillboardsBillboardsReal spheres

Слайд 13 Screen-aligned Billboard
v: [0,0,1] in eye coord.
Transform into world

Screen-aligned Billboardv: [0,0,1] in eye coord.Transform into world coord.During each frame:Rotate every n into v

coord.
During each frame:
Rotate every n into v


Слайд 14 Billboard Cloud for Extreme Model Simplification (url)

Billboard Cloud for Extreme Model Simplification (url)

Слайд 15 Application: (Quasi-)Impostor
Impostor: render 3D object into texture, in

Application: (Quasi-)ImpostorImpostor: render 3D object into texture, in various viewing anglesInstead

various viewing angles
Instead of showing the facet model, show

a polygon with correct texture

Слайд 16 Impostor-2
Usually textures are stored in a single texture

Impostor-2Usually textures are stored in a single texture object, to avoid

object, to avoid repeated binding
Use texture transform to switch

to the correct one
glGetIntegerv (GL_MAX_TEXTURE_SIZE, &size)

Слайд 17 Impostors
A billboard created on the fly
rendering a complex

ImpostorsA billboard created on the flyrendering a complex object from the

object from the current viewpoint into an image texture,

then post on a billboard)

Слайд 18 Impostors (Schaufler)
The top of figure 1 shows an

Impostors (Schaufler)The top of figure 1 shows an object for which

object for which an imposter is generated together with

its bounding box, which is used to bound the extent of the object’s picture. The imposter is chosen to lie in the plane P through the object center C normal to the direction from C to the point of view V (normal to n as shown at the bottom of figure 1). The extent of the imposter is taken as the smallest rectangle in P which contains the projection of the object’s bounding box onto P

Слайд 19 Impostors (cont)
Idea:
Project the bounding box of the object

Impostors (cont)Idea:Project the bounding box of the object to determine size

to determine size of impostor polygon
Issues
Alignment (texture placement)
Texture resolution
Invalid

impostor (require regeneration)

Слайд 20 Impostors (cont)
Rendering speed depends on the number of

Impostors (cont)Rendering speed depends on the number of pixelsUsage:A few instances

pixels
Usage:
A few instances of the object
A few frames of

the object (strategy for updating imposters)
Rendering distant objects
Movement of project image diminishes with an increased distance from viewer
Image lowpass filtered to create depth-of-field effect

Слайд 21 Impostor: texture resolution

Impostor: texture resolution

Слайд 22 Impostors Regeneration
Schaufler
βtex, βtrans, or βsize ≥ βscr

Impostors RegenerationSchauflerβtex, βtrans, or βsize ≥ βscr

Слайд 23 Problem of Billboard

Problem of Billboard

Слайд 24 Coherent Layers (Lengyel and Snyder, 1997)
Hand animators use layers

Coherent Layers (Lengyel and Snyder, 1997)Hand animators use layers to reduce

to reduce the number of cells to draw
One layer

for background, one for middle ground, one for character,…
Background layers need to be changed less frequently than foreground, slow moving less frequently than fast moving,…
Layers are composited as a final step
Coherent layers was designed to work with hardware that supports fast compositing and layer warping
Approach:
Break scene into layers by hand
At run-time, warp some layers, re-render others
Composite the layers into the frame buffer (back to front)

Слайд 25 Chicken Run (80 layers)

Chicken Run (80 layers)

Слайд 26 Depth Sprites (Nailboards)

Depth Sprites (Nailboards)

Слайд 27 Nailboards (cont)

Nailboards (cont)

Слайд 28 Hierarchical Image Caching
Use impostors in a hierarchy for

Hierarchical Image CachingUse impostors in a hierarchy for better performancePartition the

better performance
Partition the scene into a hierarchy of boxes

and create an impostor for each box
Rerendering: done only when one or more of its children’s impostors need to be updated due to movements.

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