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Texture
- Pattern of Intensity and color.
- Can be generalized to 3D texture.
- How do we get them?
- Take pictures.
- Write a program (procedural textures).
- Synthesize from examples
- How do we apply them? (Texture mapping)
- Specify a mapping from texture to object.
- Interpolate as needed.
- This can be a challenging problem, but we’ll consider simpler version.
No Textures
Image courtesy, Foley, van Dam, Feiner, Hughes
With Textures
Image courtesy, Foley, van Dam, Feiner, Hughes
Texture Image
v
u 1
Courtesy, http://titan.spaceports.com/~seymor
v^ Procedural Texture
(^7) u
Assuming 3 bits: Vwave = v % 2
v^ Procedural Texture
(^7) u
Uwave = u % 2 Vwave = v % 2 Pix(u, v) = Uwave Vwave
Example Procedural Models
Images from Texturing and Modeling: A Procedural Approach By Ebert, Musgrave, Peachey, Perlin, and Worley
Example Procedural Models
Images from Texturing and Modeling: A Procedural Approach By Ebert, Musgrave, Peachey, Perlin, and Worley
Example Procedural Textures
Images from Texturing and Modeling: A Procedural Approach By Ebert, Musgrave, Peachey, Perlin, and Worley
What is Texture?
- Something that repeats (or continues, or has
structure) with variation.
- Must separate what repeats and what stays
the same.
- Model as repeated trials of a random process
- The probability distribution stays the same.
- But each trial is different.
- This may be true (eg., pile of objects)
- Can be added structure (general shape of
mountain, plus rocky variation).
Perlin Noise
- Natural phenomenon derives its richness from
variations
- But we don’t want white noise!
- Almost all movies use some form of Perlin noise:
- James Cameron Movies (Abyss,Titanic,...)
- Animated Movies (Lion King, Moses,...)
- Arnold Movies (T2, True Lies, ...)
- Star Wars Episode I, Star Trek Movies
- Batman Movies
- Refer noisemachine.com for details
Perlin Noise
• Reproducibility
• No repeatability
• Band limited (smoothly
changing)
• User control
2D Perlin Noise
Images courtesy of Paul Bourke
Smooth Noise
1. Populate an integer grid with random
values.
2. Interpolate in between to get values at non-
integer points
- This creates a kind of smoothing
Advantages:
1. Randomness at grid points
2. Band limited
Linear Interpolation
f(x) = floor(x)(x-floor(x)) + ceiling(x)(ceiling(x)-x)
- Average of neighboring points weighted by distance to them.
Cubic Interpolation
Instead of weighting by distance, d, weight by:
1 – 3d^2 + 2|d|^3
•Smooth •Symmetric
(www.noisemachine.com – Perlin)
Multiple Octaves
How about if we introduce more
frequencies?
double fractalsum(double x, double y, double z) { double value = 0; double f;
*for(f = MINFREQ; f < MAXFREQ; f = 2) value += gnoise(x * f, y * f) / f; return(value); } Demo of assignment executable
(www.noisemachine.com – Perlin)
Fractsum 10 x 10
Turbulence 10 x 10
Spatial regularities
• Multiply intensities by sine of x
coordinates.
• Demo
Map Intensities to Color
Demo
(www.noisemachine.com – Perlin)
Nonlinear changes in intensity
Blue channel always 255, others taken from noise.
OpenGL Texturing
- Create and specify a texture object
- Create a texture object
- Specify the texture image
- Specify how texture has to be applied for each pixel
- Enable texture mapping
- Draw the textured polygons
- Identify the active texture
- Specify texture coordinates with vertices
Specify a 2D Texture Object
- glTexImage2D(GLenum target, GLint level, GLint
*internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLVoid *texels);*
- Eg: glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 128, 128, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);
- format and type used to specify the way the texels are stored
- internalFormat specifies how OpenGL should store the data internally
- width and height have to be powers of 2; you can use gluScaleImage( ) to scale
Specify how Texture is applied
- glTexParameter{if}(GLenum target, GLenum pname, TYPE param)
- target can be: GL_TEXTURE_1D, GL_TEXTURE_2D, …
pname param
GL_TEXTURE_WRAP_S GL_CLAMP, GL_REPEAT
GL_TEXTURE_WRAP_T GL_CLAMP, GL_REPEAT
GL_TEXTURE_MAG_FILTER GL_NEAREST, GL_LINEAR
GL_TEXTURE_MIN_FILTER GL_NEAREST, GL_LINEAR
Enable the Texture and Draw
- glEnable (GL_TEXTURE_2D)
- glTexCoord2f (GL_FLOAT u, GL_FLOAT v)
- Specify texture coordinates per vertex (just
as normals, color, etc).
