2D Clipping and Viewing

Question 1

What is the World Coordinate System?

Answer 1

The space in which the application model is defined.

Question 2

What is the Screen Coordinate System?

Answer 2

The space in which the image is displayed.

Question 3

What is the window?

Answer 3

The rectangle of the world we wish to display.

Question 4

What is the Interface Window?

Answer 4

The window everything is displayed in.

Question 5

What is the View-port?

Answer 5

Where the image is defined to be show, either entire screen or the interface window.

Question 6

What is a Viewing Transformation?

Answer 6

Mapping from the world to the view-port.

Question 7

What are the steps of a worldview transformation?

Answer 7

Choose window in world coordinates > Clip to the size of the window > translate it to the origin > Scale to the view-port size > Translate to the interface window.

Question 8

What is Panning?

Answer 8

Moving the window through the world.

Question 9

What is Zooming?

Answer 9

Reducing or Increasing the window size.

Question 10

What is aspect ratio?

Answer 10

The relation between the width and height of a window.

Question 11

What is Clipping?

Answer 11

Clipping is the removal of all objects or part of objects in a
modelled scene that are outside the real-world window.

Question 12

What is the Clip Window?

Answer 12

The Area to be clipped.

Question 13

What are the types of Clipping?

Answer 13

Point Clipping, Line Clipping, Area Clipping, Curve Clipping, Text Clipping.

Question 14

What is point clipping?

Answer 14

Define 4 lines making a box, if point inside display else don’t.

Question 15

When is line clip a trivial accept?

Answer 15

When the entire line is inside the clip box.

Question 16

When is line clip a trivial reject?

Answer 16

When the entire line is outside the clip box.

Question 17

What are the non-trivial cases for line clipping?

Answer 17

One end is inside the clip box while the other end is outside and when both ends are outside the clip box but pass through.

Question 18

What is Brute Force Line Clipping?

Answer 18

When you use parametric line equations to look for window intersections. It’s Computationally expensive.

Question 19

What is Cohen-Sutherland Algorithm?

Answer 19

A line clipping algorithm that segments the clipping area into nine regions and gives them a 4 bit op-code. line endpoints have corresponding op-codes.

Question 20

How does Cohen-Sutherland Algorithm handle non-trivial cases?

Answer 20

Pick endpoint outside. > Pick crossed edge (set op-code bit) > find edge intersection point > replace the outside point with new point > repeat until trivial accept or reject.

Question 21

What lines are a special case for Cohen-Sutherland Algorithm?

Answer 21

Vertical lines.

Question 22

What is the Liang-Barsky Algorithm?

Answer 22

A line clipping algorithm that uses parametric equations.Algorithm text p. 257.

Question 23

What are all the condition and the parameters for Liang-Barsky?

Answer 23

condition up <= q for k = 1,2,3,4
p1 = -dx, q1 = x0 - xwmin
p2 = dx, q2 = xwmax - x0
p3 = -dy, q3 = y0 - ywmin
q4 = dy, p4 = ywmax - y0
if pk != 0, u = qk/pk

Question 24

What is the Sutherland-Hodgman Algorithm?

Answer 24

It is a polygon clipping algorithm, go around the polygon and record valid points clip otherwise.