Paper Summaries Any takers? Texture Mapping Logistics One more - - PDF document

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Paper Summaries Any takers? Texture Mapping Logistics One more - - PDF document

Feb 02, 2024 153 likes •283 views

Paper Summaries Any takers? Texture Mapping Logistics One more announcement Electronic Arts (EA) is coming to RIT. Job related news Looking for a few (actually more than a few) good Co-op orientation gaming programmers

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SLIDE 1

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Texture Mapping

Paper Summaries

  • Any takers?

Logistics

  • Job related news

– Co-op orientation

  • Friday, Sept 16th 12:00 – 1:30pm 70-1400
  • Friday, Oct 14th 1:00 – 2:30pm Eastman Aud.

– Career Fair

  • Wednesday, Sept 28th
  • 11am – 4pm
  • Gordon Field House

– EA Job offer

One more announcement

  • Electronic Arts (EA) is coming to RIT.

– Looking for a few (actually more than a few) good gaming programmers – EA Company Presentation

  • Tuesday, October 4th
  • 6-7:30pm
  • Golisano auditorium

– Interviews

  • Wednesday, October 5th (Career Center)
  • SIGN UP IF INTERESTED!!!

Assignments

  • Checkpoint 2

– Due today.

  • Checkpoint 3

– Due Thursday – Roundoff error!

  • Checkpoint 4 / RenderMan

– To be given Thursday

Projects

  • Approx 17 projects
  • Listing of projects now on Web
  • Presentation schedule

– Presentations (20 min max) – Last 3 classes (week 10 + finals week) – Sign up

  • Email me with 1st , 2nd , 3rd choices
  • First come first served.
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SLIDE 2

2

Computer Graphics as Virtual Photography

camera (captures light) synthetic image camera model (focuses simulated lighting)

processing

photo processing tone reproduction real scene 3D models Photography: Computer Graphics: Photographic print

Remember this?

  • Bi-directional Reflectance Function

) , , , (

r r i i r

f BRDF θ φ θ φ =

At a given point, gives relative reflected illumination in any direction with respect to incoming illumination coming from any direction

Illumination Models

  • Illumination model - function or algorithm used

to describe the reflective characteristics of a given surface.

  • More accurately, function or algorithm used to

approximate the BRDF.

Phong Model

specular diffuse ambient

V) R ( N) S ( ) (

∑ ∑

  • +
  • +

=

i k i i s i i i d a a

e

L k L k L k V L

Question

  • What if Phong (or other) Illumination

models aren’t good enough?

– Texture Mapping – use an image – Procedural Shading – program your own

Texture Mapping

  • Developed in 1974 by Ed Catmull, currently

president of Pixar

  • Goal: Make Phong shading less plastic looking
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SLIDE 3

3

Texture Mapping

  • A means to define surface characteristics of

an object using an image

  • Mapping a 2D image onto a 3D surface
  • Coordinate spaces in texture mapping

– Texture space (u, v) – Object space (xo,yo,zo) – Screen space (x, y)

Texture Mapping

Watt

Texture Mapping

  • Key to texture mapping is parameterization

– 3D geometry must be expressed as a function

  • f 2 variables, u and v.

– Examples:

  • Planar
  • Spherical
  • Bi-cubic patch
  • Cylindrical

Texture Mapping

texture space (u,v)

  • bject space (xo,yo, zo)

screen space (x,y)

parameterization projection

Texture pipeline

Akenine-Moller / Haines

Texture pipeline example

Akenine-Moller / Haines

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SLIDE 4

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Projector function

  • Converts 3D point in object space (x,y,z) to

2D point in texture parameter space (u,v)

  • Examples:

– Spherical mapping – Cylindrical mapping – Planar mapping – Parametric surface mapping

Projector function

  • Spherical Mapping

Projector function – Spherical Mapping

Texture is like a rubber sheet stretched to fit model

Projector function

  • Cylindrical mapping

Projector function

  • Spherical mapping

Projector function

  • Bi-cubic surfaces
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SLIDE 5

5

Projector function – bicubic surfaces

Watt

Projector function

  • Texture Mapping Applets

http://www.cs.brown.edu/exploratories/free Software/catalogs/texture_mapping.html

Corresponder function

  • Converts from texture parameter space (u,

v) to texel space.

– Controls the way an image is applied – Examples:

  • Direct mapping
  • Use a portion of an image
  • Apply transforms
  • Out of range transforms

Texture Mapping - Direct Mapping Texture Mapping – Using a Portion of the Image

Texture Mapping – Applying Transformation

⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ 1 Matrix n Translatio Matrix Rotation Matrix Projection 1 n v u z y x

Foley/VanDam(745)

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SLIDE 6

6

Texture Mapping – out of range

Repeat (tile) Mirror (tile) clamp border

Texture mapping

  • Aliasing

– Sampling – images are discrete, not continuous. – Resolution of sampled space (in this case texture map) is not fine enough

Texture mapping

  • Aliasing- point sampling in middle of pixel - need

more!

Texture Mapping – Aliasing

Watt

Texture Mapping

  • Aliasing -because of interpolation and perspective

projection

aliased image anti-aliased image

Texture Mapping - Anti-aliasing

  • Point sample at higher resolution (sometimes very

difficult)

– Nearest

  • Pick the closest texel

– Linear

  • Take an average of surrounding texels

– Mip-Mapping

  • Multiple textures of the same image
  • Use low pass filter before sampling
  • Can sometimes use stochastic sampling to improve

results

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SLIDE 7

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Texture mapping

  • Texture Map Aliasing Applet

http://www.nbb.cornell.edu/neurobio/land/ OldStudentProjects/cs490- 96to97/anson/TextureMappingApplet/

Texture Mapping

  • Mipmaps

– Pre-calculate your texture map at many resolutions (or layers) – Store all “texture layers” in a single image. – Use “appropriate” layer when performing rendering, interpolating between levels as required – Mip == “multum in parvo”

  • Latin for “many things in a small space”

– Native support in hardware.

Mipmapping Texture Mapping

  • Mipmaps

Texture pipeline

  • Break

When we last left our hero

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SLIDE 8

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Value transform function

  • Texture maps need not be just plain old

RGB.

  • Texture == data associated with an object

– Stored in a 2D array of texels

  • Value transform function

– Transforms data into value usable by the illumination model at the shading point

Value Transform functions

  • Texel data interpretation:

– Normal displacement – Bump Mapping – Transparency Mask – Alpha Mapping – Reflection – Environment Mapping – Illumination – Light Mapping – Specular component – Gloss Mapping – Lighting intensities – Radiance Mapping

Texture Mapping- Bump Mapping

Adds roughness to surfaces Quick way to add detail to an

  • bject

Polygon remains physically flat, but appears bumpy

Jim Blinn

Texture Mapping- Bump Mapping

  • Perturbing surface normal
  • Texture map represents displacements from the

normal

  • Use perturbed normal in illumination model

Texture mapping – Bump Mapping

Bump Mapping Theory

  • If your eyes see light and dark bumps
  • Flat surfaces reflect more light
  • Bumpy surfaces reflect less
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SLIDE 9

9

Bump Mapping-Theory Bump Mapping

  • Perlin Dnoise example

Normal += Dnoise (point)

[Perlin85]

Texture Mapping

  • Bump Mapping

Alpha Mapping

  • Used to control the transparency.
  • Example:

3dimpact.com

Texture Mapping- Environment mapping

  • Create an image, representing the reflection of the

world onto an object

  • Use surrounding sphere or box, image is texture map

indexed by direction of reflection ray

  • Poor-man’s ray tracing - cheaper

Texture Mapping- Environment mapping

  • Not associated with a particular object but with

an imaginary surface surrounding the scene

– Specular Reflection – indexed by reflected ray – Diffuse - by surface normal – Transparency – refracted ray direction

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SLIDE 10

10

Environment Mapping Environment Mapping

spherical Cube map

Texture Mapping

  • Environment mapping

Texture mapping

Reflection mapping

Light Mapping

  • Texture map that describes illumination

(light sources)to apply

flipcode.com

Gloss Mapping

  • The texture that controls the specular

reflection color.

  • Modulates the the specular reflection and

the environment map.

  • Demo
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SLIDE 11

11

Texture Mapping

  • Static

– Texture map image is taken under a single lighting condition – Q: What happens when lighting conditions of the scene doesn’t match that of your texture? – A: let’s go to the video tape

Texture Mapping – Radiance Maps

  • Provides approximated radiance values, not

simply color info, as a texture.

  • Radiance map not only for the distant scene,

but in reflections from objects.

  • Radiance in map used in global illumination

solution

  • Technique used in Fiat Lux

Texture pipeline

  • Finally obtained data is applied in

illumination equation.

Layered Texture Mapping Layered Texture Mapping

  • Applet

http://users.interfriends.net/maurid/Bump Mapping.htm

Multipass Texture Rendering

  • Multiple textures for multiple parts of

illumination model rendered on multiple passes.

  • Modern hardware supports up to 10 passes
  • n a single frame.
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SLIDE 12

12

Multipass Texture Render

  • Quake III Engine

– Passes 1-4: accumulating bump map – Pass 5: diffuse lighting – Pass 6: base texture – Pass 7: Specular – Pass 8: emissive lighting – Pass 9: volumetric effects – Pass 10: screen flashes

Summary

  • Texturing Pipeline
  • Advantages of texture mapping

– Easy way to add complexity to a scene – Hardware support

  • Issues:

– Aliasing – Limited resolution (zoom in DOOM effect) – Static image

Summary

  • In this lecture, we assumed that textures

were pre-generated and saved in a file

  • Textures can also be generated on the fly

using a function or procedure…

– But that’s for next time…

  • Questions?