High Performance Visualization I Week 3

1
High Performance Visualization I Week 3

• Instructors
• Dr. James Sochacki
• Dr. Ramon Mata-Toledo
• Lab Instructors
• Joshua Blake
• Justin Creasy

2
Review

• 3D Basics
• Processing input from keyboard and mouse
• Homework Terrain Program
• Due Thursday at lab
• Share? Problems?

3
Today

• More advanced 3D concepts
• Ortho vs Perspective
• Projections
• More on Matrices
• Coding standards
• Textures

4
Review

• Process of transforming a vertex from world
  coordinates into rasterized pixels

5
Vertex Transformations

• Each vertex is a 4-d vector
• Transform by applying the appropriate 4x4 matrix
  to the coordinates of the vertex.
• If v is our vertex
• And M is our 4x4 matrix
• Then Mv is our image of v under the
  transformation of M

6
Making my life easier

• For now, just understand that when you specify a
  point, either 2-d or 3-d, internally the computer
  stores it as a 4-d point
• We have already talked about the X, Y, and Z
  coordinates. We skipped the W coordinate
• W is basically 1/depth
• For now, understand it is there and will affect
  transformations and when it is not specified its
  value is 1
• x, y, z, w

7
Counteracting commands

• Some transformations can counter what is done by
  another transformation (or add to it)
• Transformations affect the current matrix, and
  are cumulative
• Using a viewing transformations we can pull our
  viewport away from the image, making it smaller
• We could instead also use a modeling
  transformation to move the model away from the
  viewport
• To counter a transformation, use the inverse
  matrix

8
Examples of Matrices

• glLoadIdentity()
• Identity Matrix
• Any vector multiplied by the identity doesnt
  change. ( Iv v )
• The inverse of the identity is itself.

9
More examples

• Translate, Scale, and Rotate modify the current
  matrix (Modelview, Projection, etc.)
• glTranslate(x, y, z) generates T, where

10
More examples

• glScale(x, y, z) generates S, where
• Rotation is more complicated.

11
The Modelview Matrix

• This positions your vertices and models in the
  world
• Include rotating, scaling, and translating the
  model
• Raw vertices aremultiplied by the ModelView
  matrix

12
Push and Pop

• glPushMatrix saves the current state of the
  active matrix (usually the modelview)
• Saved on a stack
• glPopMatrix retrieves the state
• Used for complex objects
• glPushMatrix()
• glTranslatef(10, 0, 0) (changes the origin)
• Draw something with respect to origin
• glPopMatrix()
• Now the thing you drew is centered around (10,
  0, 0)

13
Projection Matrix

• Determines what is visible
• Clipping planes are defined
• Analogous to positioning a camera on a tripod
• Produces a view of your world

14
Projection Transformation

• This is the process of determining the shape of
  the volume you are viewing
• Following the camera analogy, its like deciding
  what lens to use
• Two types of projections are orthographic and
  perspective

15
Orthographic

• Maps object directly onto screen without
  affecting its relative size
• Useful when the measurements of objects is more
  important than how the object actually looks
• Ex Architectural and computer aided designing
• Parallel lines stay parallel

16
Perspective

• This is the more commonly used projection
• Attempts to match the graphics to how they would
  look in everyday life
• Specified by the glFrustrum() or gluPerspective()
  command
• Objects further away appear smaller, etc. and
  there is a vanishing point
• Parallel lines converge

17
Viewport Transformation

• This is the process of determining what is
  viewable on screen and matching pixels to their
  correct color, shade, etc. (also called
  rasterization)

18
How this pertains to you

• While this is the order the computer processes
  your graphics, its not necessarily how you think
  about it
• You create vertices, lines, and so forth, which
  are affected by the matrices.
• To create viewing transformations,
  transformations must be performed on these
  matrices.

19
Textures Mapping

• Pastes an image onto a polygon
• glTexCoord2d(u, w) specifies the texture
  coordinates

(1, 1)
(0, 1)
w
(0, 0)
(1, 0)
u
20
Texture Coordinates

• Use texture coordinates to specify what part of
  the active texture will align with the following
  vertices
• glTexCoord2f(0, 0)
• glVertex3f(0, 0, 0)
• glTexCoord2f(0, 1)
• glVertex3f(0, 2, 0)
• glTexCoord2f(1, 1)
• glVertex3f(2, 2, 0)
• glTexCoord2f(1, 0)
• glVertex3f(2, 0, 0)

The vertices do not have to be same as the
texture coordinates!
21
Texture Coordinates

• glTexCoord2f(0, 0)
• glVertex3f(0, 0, 0)
• glTexCoord2f(0, 1)
• glVertex3f(0, 2, 0)
• glTexCoord2f(1, 1)
• glVertex3f(1, 2, 0)
• glTexCoord2f(1, 0)
• glVertex3f(1, 0, 0)

22
Texture Coordinates

• glTexCoord2f(0, 0)
• glVertex3f(0, 0, 0)
• glTexCoord2f(0, .5)
• glVertex3f(0, 2, 0)
• glTexCoord2f(1, .5)
• glVertex3f(2, 2, 0)
• glTexCoord2f(1, 0)
• glVertex3f(2, 0, 0)

23
Example code
24
Lighting

• Next week!

25
Reference

• Neat terrain stuff
• http//www.lighthouse3d.com/opengl/terrain/
• www.gamedev.net (The Redbook)
• Chapter 9 for textures
• Chapters 3 and Appendix F for matrices

26
Homework

• Add Textures to the Terrain
• Start to form an organized idea of what the world
  is it could be abstract patterns or concrete
  idea from the real world, but it should
  definitely be understandable
• Add at least two textures, at least one to the
  terrain itself, and one to the object on the
  terrain from last week
• Create more complex height functions, either
  taking ideas from the lecture/example code or
  from a terrain tutorial online
• Continue to be creative