# Computer Graphics: Question Set – 08

#### What is Polygon, edge and vertex?

A **polygon **is a closed figure composed of interconnected lines. A polygon is a shape with multiple sides that is represented by line segments. The line segments that constitute the polygon’s boundary are known as polygon **edges**, and the endpoints of the edges are known as polygon **vertices**.

#### Define the phrase “convex polygon.”

The angle between each consecutive pair of edges of a convex polygon is always less than 180^{o}.

For a convex polygon, if we choose any two random points inside the polygon and connect them with a line, all of the points on the line are unquestionably inside the polygon.

Figure depicts examples of convex polygons.

#### Define the phrase “concave polygon.”

A concave polygon has an angle greater than 18^{o} between at least one set of successive edges.

A concave polygon always has a pair of vertices inside it, and when joined by a line segment, part of the line segment falls outside the polygon.

Examples of concave polygons are illustrated in Figure.

#### What do you mean by complex polygon?

Complex polygons are polygons that are neither convex nor concave. Self-intersecting or overlapping polygons are complex polygons.

Examples of complicated polygons can be found in the following figure:

#### Describe and explain different polygon formats.

The graphics package determines how the polygon is represented in the system.

There are three techniques to representing the polygon:

**Polygon drawing primitive approach:**Some graphics packages offer polygon as a fundamental image shape; in this case, the polygon is represented as a whole entity. Such polygons render quickly.**Trapezoid primitive approach**: In certain graphics programs, a polygon is approximated as a series of trapezoid primitives.**Line and point approach**: The polygon in this approach is defined by end point coordinates. To form the polygon, a line is generated between each end point.

#### Enlist advantages and disadvantages of Boundary fill algorithm

**Advantages:**

- Simple and easy to apply.
- Works with any sort of polygon.

**Disadvantages:**

- Due of recursion, substantial stacking is required.
- If the boundary is provided with various colors, it will not operate.
- It is necessary to indicate the seed point enclosed within the polygon.
- The background color should be used to fill the polygon.
- Uses a lot of stacking.
- Require more memory.
- Not suitable for the large polygon.

#### State pros and cons of Flood fill algorithm

**Advantages:**

- Simple
- Easy to implement.
- The boundary fill method is incapable of handling objects with multi-color boundaries, whereas flood fill is.

**Disadvantages:**

- Extensive stacking is required.
- Slow in nature.
- Not suitable for large polygons

#### What is the difference between the Seed Fill and Scan Line Algorithms?

Sr. No. | Seed fill algorithm | Scan line algorithm |

1. | Simple to implement. | Very complex in nature. |

2. | Operates in screen space. | Operates in screen and / or object space. |

3. | Require system call to get pixel intensity . | It is device independent. |

4. | Need to specify seed point contained within the polygon. | No need to specify seed point. |

5. | Need extensive stacking. | No need of stacking. |

6. | Generally used in graphics packages. | Typically used in interactive rendering. |

7. | Not suitable for Z-Buffer. | Suitable for Z-Buffer. |

**Scholarly Article: **Generation of simple polygon from ordered points. Click to read.