2024-CS426FZ-January
Q1
(a) Explain the interactive graphics and passive graphics systems with examples.
Lecture 1 - In interactive computer graphics, user have some controls over the picture. User can make any change in the produced image
- Example: video game
- In passive computer graphics, the picture is produced on the monitor. User does not have any control over the images that are displayed.
- Example: TV show
(b) Describe the applications of computer graphics in the field of entertainment and in the creation of graphical user interfaces.
Lecture 1 - Entertainment: A way of interacting with a computer using the Icon, Menu, button easily.
- GUI: Graphics scene generated for the movie.
(c) Explain the functions of each and every component of a direct view storage tube (DVST) display device.
Lecture 1 There are two guns used in DVST:
- Primary Gun: It is used to store the picture information.
- Flood / Secondary Gun: It is used to display a picture on the screen.
(d) Distinguish between 2-dimensional and 3-dimensional representations in computer graphics. Include diagrams for each type with your answer.
Lecture 2 
Q2
(a) Explain the 2D translation technique with appropriate diagrams.
Lecture 2 
(b) A 3D triangle with coordinate points is given by . Apply reflection on the xy plane and find the new coordinate points of triangle.
Lecture 2 (c) A 3D object that has coordinates points and the scaling parameters are 3 along the x-axis, 4 along the y-axis and 4 along the z-axis. Apply scaling to find the new coordinates of the object.
Lecture 2 Q3
(a) Explain the characteristics of seed fill and scan line methods in filled region processing, use diagrams to support your explanation.
Lecture 3 - Seed fill selects a starting point called seed inside the boundary of the polygon. It can be further classified into twoalgorithms:
- Flood fill defines a region in a polygon. It colors the whole area through interconnected pixels by a single color. t is similar to the bucket tool used in the paint program.
- Boundary fill uses polygon boundaries. It is also called an edge fill algorithm.
- Scan line is an area-filling algorithm that fill colors by scanning horizontal lines. These lines intersect the boundaries of the polygon and fill colors between the intersection points.
(b) State the digital differential analyzer (DDA) line drawing algorithm.
Lecture 3 - Step 1: Start.
- Step 2: We consider starting point as , and ending point .
- Step 3: Now, we have to calculate Δx and Δy.
- Step 4: Now, we calculate three cases.
- Case 1: If
- Case 2: If
- Case 3: If
- Step 5: We will repeat step 4 until we find the ending point of the line.
- Step 6: Stop.
(c) A line has a starting point and ending point . Apply the Bresenham’s Line Drawing algorithm to plot a line. 🧮
Lecture 3 （原题）- …
Q4
(a) Describe the characteristics of all-or-none string-clipping and all-or-none character-clipping in the text clipping technique. Include suitable diagrams with your answer.
Lecture 4 - All-or-none string-clipping
- If all of the string is inside a clip window, we keep it.
- Otherwise, the string is discarded.
- All-or-none character-clipping discards only those characters that are not completely inside the window.
(b) What is point clipping, explain the point clipping algorithm.
Lecture 4 - Step 1: set the value of and coordinates for the window.
- Step 2: set the coordinates of a given point .
- Step 3: check the conditions.
- Step 5: Stop.
(d) Describe the diffuse reflection and specular reflection technique of light. Include a diagram with your answer.
Lecture 5 - Diffuse Reflection
- occurs on the surfaces which are rough
- comes from a specific direction
- light reflected with equal intensity in all directions
- Brightness depends on theta angle between surface (N) and the direction to the light source (L)
- Position of viewer is not important
- Specular Reflection
- When light falls on any shiny or glossy surface
- Most of it is reflected back
顺便补充「环境光」的知识点
- Ambient
- Non-directional light source
- Light gets reflected so many times from so many surfaces it appears to come equally from all directions
- Intensity is constant. It is not affected by anything
Q5
(a) Discuss different types of light sources which can be used to light a scene.
Lecture 5 - Point Sources emit light from a single point in all directions.
- The intensity of the light decreasing with distance
- Example: A bulb in a room
- Parallel Sources can be considered as a point source which is far from the surface.
- Example: The sun
- Distributed Sources rays originate from a finite area
- Example: A tube light
(b) Explain the ray tracing rendering technique with appropriate diagram.
Lecture 5 - The basic concept of this method is to follow light on its way from the light source to the screen.
- It estimates what kind of color is displayed on the pixel where the light falls.
(c) Describe the functions of z-buffer.
Lecture 5 - It is used for hidden surface detection.
- For each pixel on the display screen, we keep a record of the depth (also called z value) of an object within the pixel that lies closest to the observer.
(d) Explain the texture-mapping technique in rendering. Include a suitable diagram with your answer.
Lecture 5 - A method of implementing information to surfaces.
- The pattern of the surface is considered as texture.
- Texture mapping is applied in wallpaper, paint etc.
课件原图如上，但考试黑笔画这个还是太抽象了，可以考虑下面的示例
