ch6Graphucs

Question 1

What is clipping in computer graphics?

Answer 1

It’s the process of determining which parts of objects should be displayed and which should be discarded.

Question 2

Why is clipping necessary?

Answer 2

To avoid rendering objects outside the viewing area and improve performance.

Question 3

What does OpenGL do regarding clipping?

Answer 3

It performs clipping automatically, but understanding the process is important.

Question 4

What are the main topics under clipping?

Answer 4

Windowing concepts, point clipping, line clipping, and polygon clipping.

Question 5

What is windowing?

Answer 5

Selecting a portion of a scene in world coordinates to display on the screen.

Question 6

What are world coordinates?

Answer 6

Coordinates that define objects in the entire scene.

Question 7

What defines the horizontal and vertical limits of the window?

Answer 7

wxmin, wxmax for horizontal; wymin, wymax for vertical.

Question 8

What happens to objects outside the window?

Answer 8

They are clipped and not displayed.

Question 9

Why do we use a clipping window?

Answer 9

To reduce computational cost and display only the visible portion of a scene.

Question 10

What is the condition for a point to be visible?

Answer 10

wxmin ≤ x ≤ wxmax and wymin ≤ y ≤ wymax.

Question 11

What happens if a point doesn’t meet the condition?

Answer 11

It is clipped.

Question 12

What is line clipping?

Answer 12

Determining if a line is fully, partially, or not at all within a clipping window.

Question 13

What if both endpoints of a line are inside the window?

Answer 13

The line is not clipped.

Question 14

What if one endpoint is inside and the other is outside?

Answer 14

The line is partially clipped.

Question 15

What if both endpoints are outside?

Answer 15

Further checks are needed to determine if it intersects the window.

Question 16

What is brute force line clipping?

Answer 16

A basic method of checking line visibility through boundary intersection calculations.

Question 17

What are the four window boundaries?

Answer 17

Left, right, top, bottom.

Question 18

Why is brute force clipping inefficient?

Answer 18

It requires many calculations, which are costly in large scenes.

Question 19

What does ‘TA’ stand for in brute force?

Answer 19

Trivially Accepted.

Question 20

What does ‘TR’ stand for in brute force?

Answer 20

Trivially Rejected.

Question 21

When is a line trivially accepted (TA)?

Answer 21

When both endpoints lie inside the clipping window.

Question 22

When is a line trivially rejected (TR)?

Answer 22

When both endpoints lie outside the same boundary.

Question 23

What happens if a line is neither TA nor TR?

Answer 23

Check for intersections with the window edges.

Question 24

What are the two outcomes for lines with both endpoints outside?

Answer 24

Discard if completely outside or clip if it intersects the window.

Question 25

Which mathematical concept helps find the intersection point?

Answer 25

The equation of the line.

Question 26

If a line goes from (1,1) to (10,5), and window xmax=4, what part is visible?

Answer 26

From (1,1) to the intersection point at x=4.

Question 27

What must be checked before accepting the intersection point?

Answer 27

If it lies within the segment's range.

Question 28

Why can't we apply brute force to every line in large scenes?

Answer 28

It becomes too slow due to high computational cost.

Question 29

What is the Cohen-Sutherland algorithm?

Answer 29

An efficient method for line clipping that reduces the number of intersection tests.

Question 30

Who developed the Cohen-Sutherland algorithm?

Answer 30

Ivan Sutherland and an associate named Cohen.

Question 31

How is the world space divided in this algorithm?

Answer 31

Into 9 regions using 4-bit region codes.

Question 32

What does the region code 0000 represent?

Answer 32

The point is inside the window.

Question 33

What does a region code like 1010 indicate?

Answer 33

The point is above and to the right of the window.

Question 34

What operation is used to check rejection?

Answer 34

Bitwise AND of the two region codes.

Question 35

What if both endpoints have region code 0000?

Answer 35

The line is trivially accepted.

Question 36

What if the bitwise AND of two region codes ≠ 0?

Answer 36

The line is trivially rejected.

Question 37

What if a line cannot be trivially accepted or rejected?

Answer 37

Find intersection points with the window boundaries.

Question 38

What does labeling points mean in this algorithm?

Answer 38

Assigning 4-bit region codes to each endpoint.

Question 39

What do the 4 bits represent in the region code?

Answer 39

Top, bottom, right, and left of the window.

Question 40

What happens to a line from P9 (inside) to P10 (outside bottom)?

Answer 40

It's clipped at the bottom and partially drawn.

Question 41

What happens to a line from P3 (left outside) to P4 (top outside)?

Answer 41

It is clipped and not drawn.

Question 42

What happens to a line from P7 (below) to P8 (right)?

Answer 42

It is clipped at both ends and the visible portion is drawn.

Question 43

How are intersection points calculated in this algorithm?

Answer 43

Based on which boundary the point is outside of.

Question 44

What is the advantage of this algorithm?

Answer 44

Fewer intersection calculations and early rejection.

Question 45

What does a 1 in a region code bit indicate?

Answer 45

That the point is outside the window in that direction.

Question 46

When is intersection calculation necessary?

Answer 46

If both endpoints have different region codes but bitwise AND is zero.

Question 47

Why use bitwise operations in clipping?

Answer 47

They are fast and efficient for testing.

Question 48

Can we apply line clipping directly to polygons?

Answer 48

No, it would break the polygon into disjoint segments.

Question 49

What is the requirement after polygon clipping?

Answer 49

The result must be a closed, connected polygon.

Question 50

What does the Sutherland-Hodgman algorithm do?

Answer 50

Clips polygons by processing vertices against each boundary.

Question 51

How are boundaries processed in Sutherland-Hodgman?

Answer 51

One at a time — left, right, bottom, top.

Question 52

What happens after each boundary clip?

Answer 52

A new set of vertices is generated.

Question 53

What is Case 1 in Sutherland-Hodgman?

Answer 53

First vertex outside, second inside → add intersection and second vertex.

Question 54

What is Case 2 in Sutherland-Hodgman?

Answer 54

Both vertices inside → add second vertex.

Question 55

What is Case 3 in Sutherland-Hodgman?

Answer 55

First vertex inside, second outside → add intersection only.

Question 56

What is Case 4 in Sutherland-Hodgman?

Answer 56

Both vertices outside → add nothing.

Question 57

What is the purpose of saving intersection points?

Answer 57

To form the new clipped polygon.

Question 58

How many boundaries are checked in total?

Answer 58

Four.

Question 59

Can this algorithm handle concave polygons well?

Answer 59

No, it may introduce extraneous lines.

Question 60

What kind of polygons can Weiler-Atherton handle?

Answer 60

Concave polygons and polygons with holes.

Question 61

What data structure is used in Weiler-Atherton?

Answer 61

Linked list.

Question 62

What is the main idea of Weiler-Atherton?

Answer 62

Follow polygon boundary for inside entries, and window boundary for outside exits.

Question 63

What are the two paths followed in Weiler-Atherton?

Answer 63

Polygon path and window boundary path.

Question 64

What is the output of Weiler-Atherton?

Answer 64

One or more closed polygons.

Question 65

What are the two types of clipping?

Answer 65

Line clipping and area (polygon) clipping.

Question 66

What happens when only a portion of an object lies in the window?

Answer 66

That portion is kept, rest is clipped.

Question 67

What is the goal of clipping algorithms?

Answer 67

Improve rendering efficiency and avoid drawing outside areas.

Question 68

Which algorithm uses 4-bit region codes?

Answer 68

Cohen-Sutherland.

Question 69

Which algorithm works by comparing edges against boundaries in turn?

Answer 69

Sutherland-Hodgman.

Question 70

How do you find outcode bits for a point?

Answer 70

Compare its coordinates to the window boundaries.

Question 71

In Cohen-Sutherland, what does it mean if both outcodes are zero?

Answer 71

The line is fully inside.

Question 72

What if outcodes share a common bit (e.g., both top)?

Answer 72

The line is fully outside.

Question 73

In Sutherland-Hodgman, what is output after processing all boundaries?

Answer 73

The final clipped polygon.

Question 74

What is the clipping window defined by?

Answer 74

wxmin, wxmax, wymin, wymax.

Question 75

What's the difference between windowing and clipping?

Answer 75

Windowing selects the visible region; clipping discards the non-visible parts.

Question 76

What type of clipping can handle polygons with holes?

Answer 76

Weiler-Atherton.

Question 77

What is scan conversion?

Answer 77

The process of converting primitives into pixels.

Question 78

Which method is slower, brute force or Cohen-Sutherland?

Answer 78

Brute force.

Question 79

Which polygon algorithm can introduce extra lines in concave shapes?

Answer 79

Sutherland-Hodgman.

Question 80

Which clipping algorithm is suitable for real-time systems?

Answer 80

Cohen-Sutherland due to efficiency.

Question 81

A point is clipped if it is __________ the window.

Answer 81

Outside.

Question 82

__________ clipping is easier than line clipping.

Answer 82

Point.

Question 83

A region code of 0001 means the point is __________ the window.

Answer 83

Below.

Question 84

The brute force method calculates line __________.

Answer 84

Intersections.

Question 85

Sutherland-Hodgman processes one __________ at a time.

Answer 85

Boundary.

Question 86

A polygon must remain __________ after clipping.

Answer 86

Closed.

Question 87

The Weiler-Atherton algorithm can output __________ polygons.

Answer 87

Multiple.

Question 88

Region codes help to __________ lines quickly.

Answer 88

Accept or reject.

Question 89

Lines outside the same region are __________ rejected.

Answer 89

Trivially.

Question 90

The visible part of a line lies between P0 and __________.

Answer 90

The intersection point.

Question 91

(T/F) Brute force is the most efficient clipping algorithm.

Answer 91

False.

Question 92

(T/F) Cohen-Sutherland uses region codes to avoid unnecessary intersection tests.

Answer 92

True.

Question 93

(T/F) Windowing changes object geometry.

Answer 93

False.

Question 94

(T/F) Weiler-Atherton can be used for convex and concave polygons.

Answer 94

True.

Question 95

(T/F) Sutherland-Hodgman is preferred for complex polygons with holes.

Answer 95

False.

Question 96

(T/F) Clipping can affect performance in rendering.

Answer 96

True.

Question 97

(T/F) Clipping should always be done manually in OpenGL.

Answer 97

False.

Question 98

(T/F) Region codes have only two bits.

Answer 98

False.

Question 99

(T/F) In Cohen-Sutherland, region code 0000 means the point is outside.

Answer 99

False.

Question 100

(T/F) The top bit in the region code represents the point being above the window.

Answer 100

True.