Texture Mapping and Programmable Graphics Hardware: A Deep Dive, Slides of Computer Graphics

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Texture Mapping and

Programmable Graphics Hardware

Today

• More mapping

• Finish up Texture Mapping

• Bump Maps

• Displacement Maps

• Discussion of programmable graphics hardware

• Discussion of class project

BSP Tree Illustration

• Let’s see an example (in 2D, not 3D)
  • Here, a line divides the plane into two half-

planes

Space BSP Tree

A

A

X

B C

C

X

B

Y

D

E E

Y

D

BSP Tree Review

• Use implicit planes to carve up space (and

the geometry in it) into distinct subspaces

• One BSP tree can be used for any

viewpoint

• Can be used to implement a painter’s

algorithm

• Or to speed up a raytracer...
  • We’ll be seeing this again
• Any questions?

Sampling Issues

• So we can define the mapping, and it

works fine

• As long as the size of the rendered image is

approximately the same size as the texture

source

• What if the textured polygon renders

much smaller in the final image

than the original texture?

• How about much bigger?

Mip-mapping to the Rescue

• Mip-mapping is a technique that creates

multiple resolutions of an image

• i.e. Takes a 512x512 image and filters it to

create 256x256, 128x128, 64x64, ..., 1x

versions of it

• Then, when you’re looking up your

texture coordinates, it uses the most

appropriate mip-map level

• Or, more likely, interpolates between the two

closest

Assigning Texture Coordinates

• We generally want an even sharing of

texels (pixels in the texture) across all

triangles

• But what about this case?
  • Want to texture the teapot:

Do we want this? Or this? Docsity.com

Planar Mapping

• Just use the texture to fill all of space
  • Same color for all z-values
  • (u, v) = (x, y)

Spherical Mapping

• “Wrap” the texture around your object
  • Like a globe
  • Same color for all pixels with the same

angle

• u = ϕ / 2π v = (π - θ) / π

Cube Mapping

• Not quite the same as the others
  • Uses multiple textures (6, to be specific)
• Maps each texture to one face of a cube

surrounding the object to be textured

• Then applies a planar mapping to each face

Environment Mapping Example

Solid Textures

• We’ve talked a lot about 2D (image) textures
  • Essentially taking a picture and pasting it on a

surface

• No reason a texture HAS to be 2D, though
  • Can have 1D textures (not that interesting)
  • Can have 3D textures

Texture Mapping Review

• Texture mapping is a relatively simple way

to add a lot of visual complexity to a

scene

• Without increasing its geometric complexity
• Use mip-mapping to alleviate sampling

problems

• There are infinitely many possible

mappings

• Usually want to use the most “similar” one
  • Texturing a plane? Use planar
  • Texturing a sphere? Use spherical Docsity.com

Other Mapping Techniques

• So, now we know some things about

texture mapping

• Allows us to change the color of simple

geometry

• But color isn’t the only property a

point can have

• Normals
  • Bump mapping
• Location
  • Displacement Mapping