CS480

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CS480

• Chap 0. Overview
• Chap 1. Graphics Systems and Models
• Chap 2. Graphics Programming
• Chap 3. Input and Interaction
• Chap 4. Geometric Objects and Transformations
• Chap 5. Viewing
• Chap 6. Shading
• Chap 7. Implementation
• Chap 8. Working with Models
• Chap 9. Discrete Techniques
• Chap 10. Curves and Surfaces
• Chap 11. Procedural Methods

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Chap 9. Discrete Techniques

• 9-1. Buffers and Mappings
• 9-2. Texture Mapping
• 9-3. Environmental Maps
• 9-4. Bump Maps
• 9-5. Writes into Buffers
• 9-6. Bits and Pixel Operations in OpenGL
• 9-7. Compositing Techniques
• 9-8. Use of the Accumulation Buffer
• 9-9. Sampling and Aliasing

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Graphics Pipeline
Application-specific processing
Pixel processing
Polygon processing
Scene processing
Scene graph
Display list
Frame buffer
Z- buffer
Texture memory
Past - No access to frame buffer Present -
Access is needed for texture mapping,
anti-aliasing, compositing,
alpha-blending.
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Graphics Pipeline
Application-specific processing
Pixel processing
Polygon processing
Scene processing
Scene graph
Display list
Frame buffer
Depth buffer
Texture memory
(x, y), Z, (R,G,B,A), (T, s,t)
(X, Y, Z), M
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9-1. Buffers and Mapping

• So far,
• frame buffer,
• depth (z) buffer.
• More realism
• not by modeling,
• but at the scan conversion.

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• More realistic rendering
• during the scan conversion.
• first, break the surface into small pieces (
  fragments).
• 1) Texture mapping
• Color of a fragment is determined by
• fixed pattern
• texture-generation algorithm
• real image
• 2) bump mapping
• Surface normal of a fragment is determined by
• the bump map
• 3) Environmental (reflection) mapping
• false ray-tracing

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9-2. Texture Mapping
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• Texture mapping outline

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parametric modeling
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T(s,t)
texture mapping
projection
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texel
fragment
pixel
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• Consideration 1
• Concept is simple, but ...
• 2D (texture map) ---gt 3D (object surface) is
  not easy because ...
• A pixel defines an area, not a point.

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• Consideration 2
• Texture mapping may produce aliasing effects,
• especially with the forward mapping.
• Better do the backward mapping. (screen coord
  ---gt texture coord)

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• Mapping methods
• 1) (s, t) texture map ? P (u, v) target
  surface

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• 2) T (s, t) ---gt intermediate surface ---gt P
  (u, v)
• (cylinder, sphere, box)

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Texture mapping in OpenGL
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• Define a texture map.
• glTexImage2D (GL_TEXTURE_2D, level, components,
• width, height,
• border, format, type, tarray )
• Enable the texture map
• glEnable (GL_TEXTURE_2D)
• Assign texture coordinated to vertices
• glTexCoord2f (s, t)

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• glBegin (GL_QUAD)
• glTexCoord2f (0.0, 0.0)
• glVertex2f (x1, y1, z1)
• glTexCoord2f (1.0, 0.0)
• glVertex2f (x2, y2, z2)
• glTexCoord2f (1.0, 1.0)
• glVertex2f (x3, y3, z3)
• glTexCoord2f (0.0, 1.0)
• glVertex2f (x4, y4, z4)
• glEnd( )

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• aliasing
• A pixel is larger than one texel. (magnification)
• A pixel is smaller than one texel. (minification)
• Get the nearest texel.
• Compute the average (typically 2 by 2).

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• magnification

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• minification

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• mipmapping
• To deal with minification aliasing.
• gluBuild2DMipmaps (GL_TEXTURE_2D, 3, 64, 64,
• GL_RGB, GL_UNSIGNED_BYTE,
• my_texels )

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• texture and shading
• modulation
• decaling
• transparency
• interpolation
• linear interpolation
• perspective correction

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• Texture generation

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9-3. Environmental Map
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• mirror effect, reflection on a metal ball
• basic idea

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• method
• 1. Set up an imaginary camera.
• 2. Remove the object.
• 3. Render the image for the imaginary camera.
• (This will create an environmental map.)
• 4. Treat the environmental map as a texture.
• 5. Perform texture mapping.

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Jan van Eyck (1390 1441) - ??? ??? (?)
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9-4. Bump Maps

• Creating a realistic non-smooth surface
• (e.g., orange)
• i) surface modeling
• ii) texture mapping
• What if change the light direction?
• iii) bump mapping
• Perturb the normal vector.
• Do not perturb the surface geometry itself.

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