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Computer Graphics Midterm Exam Solutions Fall 2010 at RPI (ECSE-4750), Exams of Computer Graphics

The solutions for the midterm exam of the computer graphics course (ecse-4750) at rensselaer polytechnic institute in fall 2010. It covers topics such as matrix multiplication for projection, opengl primitives, event loop, z-buffer, homogeneous coordinates, and more.

Typology: Exams

2011/2012

Uploaded on 02/17/2012

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Page 1Midterm F 2010 Solution (Computer Graphics Fall 2010)
4/25/2011 7:10:56 PMhttp://www.ecse.rpi.edu/Homepages/wrf/pmwiki/ComputerGraphicsFall2010/MidtermF2010Solution
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ECSE-4750 COMPUTER GRAPHICS, RENSSELAER POLYTECHNIC
INSTITUTE, FALL 2010
MIDTERM F2010 SOLUTION
Computer Graphics Fall 2010 group home
Search
ANSWERS
ECSE-4750 Computer Graphics, Rensselaer Polytechnic Institute, Midterm Exam, Fall 2010
NAME: _______________________________ _____
EMAIL:___________________________ RIN:______________
14 Oct 2010 4-5:30
Answer every question .There are 5 pages with 22 questions, total 44 points.
For 2 questions, you may write free for your answer (and get 2 points each).
This exam is open book : you may use calculators and any paper books and notes that you brought with you. You may not use computers
or communication devices, or share material with other students .
1. _____/2 Why do we want to make projection into a matrix multiplication?
So we can combine it with all the other matrix operations (translation, rotation, scaling).
2. _____/2 Why does OpenGL contain primitives, like triangle strips, that are not necessary (since you could draw the triangles
separately)?
It's more efficient since fewer vertices are needed than if you drew each triangle separately.
3. _____/2 What is the event loop?
It's what your OpenGL program transfers to as its last action . The loop then waits for inputs , such as mouse clicks. For each input, it
calls the appropriate callback routine, if you've registered one. On its return, the loop waits for the next input, and repeats.
4. _____/2 What does this do :
glutDisplayFunc(display)
It registers the user routine display as the display callback.
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ECSE- 4750 C OMPUTER GRAPHICS, RENSSELAER P OLYTECHNIC

INSTITUTE, F ALL 2010

M IDTERM^ F 2010 S OLUTION

Computer Graphics Fall 2010 group home Search

ANSWERS

ECSE-4750 Computer Graphics, Rensselaer Polytechnic Institute, Midterm Exam, Fall 2010

NAME: ____________________________________

EMAIL:___________________________ RIN:______________

14 Oct 2010 4-5: Answer every question.There are 5 pages with 22 questions, total 44 points. For 2 questions, you may write free for your answer (and get 2 points each). This exam is open book : you may use calculators and any paper books and notes that you brought with you. You may not use computers or communication devices, or share material with other students.

  1. _____/2 Why do we want to make projection into a matrix multiplication? So we can combine it with all the other matrix operations (translation, rotation, scaling).
  2. (^) separately)?_____/2 Why does OpenGL contain primitives, like triangle strips, that are not necessary (since you could draw the triangles It's more efficient since fewer vertices are needed than if you drew each triangle separately.
  3. _____/2 What is the event loop? calls the appropriate callback routine, if you've registered one. On its return , the loop waits for the next input, and repeats.It's what your OpenGL program transfers to as its last action. The loop then waits for inputs, such as mouse clicks. For each input, it
  4. _____/2 What does this do: glutDisplayFunc(display) It registers the user routine display as the display callback.
  1. _____/2 What does this do: glMatrixMode(GL_PROJECTION); Tells OpenGL the future matrix modification routines will modify the projection matrix (until glMatrixMode is called again ).
  2. ____/2 Since the mydisplay routine takes no arguments, how do you get data from the main program to it? Global variables.
  3. ____/2 What's the normal to the plane 5x+2y+3z=1? Your answer should be normalized.

Unnormalized: (5,2,3), but its length is. So, the normalized normal is

  1. ____/2 Give 4 advantages of homogeneous coordinates.

Therefore parallel and perspective projections are the same. When a curve is defined by control points, those points can be weightedTranslation is a matrix multiply. So is projection. Points at^ can be represented. All pairs of lines, even parallel, intersect. individually. A circle can be exactly represented as a parametric homogeneous polynomial.

  1. ____/2 What feature in OpenGL is used to display the closest object when several objects overlap the same pixel? Z-buffer.
  2. ____/2 Consider this sequence of calls: glColor3f(1.,1.,1.);glColor3f(0.,1.,0.); glVertex3f(1.,1.,1.);glVertex3f(2.,2.,2.); a. (^) What color is the vertex (1,1,1)? green, i.e., (0,1,0). b. What color is the vertex (2,2,2)? green, i.e., (0,1,0).
  3. ____/2 Give the 4x4 homogeneous matrix for a 90 degree rotation about the Y axis.

M

  1. ____/2 Since the Z buffer looks so useful , why is it not enabled by default? Efficiency.
  2. ____/2 Why do we like to group different physical input devices into the same logical input device?

matches how the user sees the system and how the system processes the data.If they provide the same type of input, then considering them as the same logical device is a reasonable level of abstraction. It

  1. ____/2 Which one of the following code fragments would you be more likely to see? Why? Could the other one still be legal andgenerate a useful picture? Why? a. (^) glMatrixMode(GL_MODELVIEW);this? glLoadIdentity();glMatrixMode(GL_PROJECTION);