Module Contact: Dr Rudy Lapeer (CMP) Copyright of the University of East Anglia Version 1

Transcription

1 UNIVERSITY OF EAST ANGLIA School of Coputing Sciences Main Series UG Exaination GRAPHICS 1 CMP-5010B Tie allowed: 2 hours Answer THREE questions. Notes are not peritted in this exaination Do not turn over until you are told to do so by the invigilator. CMP-5010B Module Contact: Dr Rudy Lapeer (CMP) Copyright of the University of East Anglia Version 1

2 -2-1. Assue you are prograing an asteroids gae in OpenGL where the user is required to fly a spacecraft around a collection of randoly oving asteroids (rock-like objects). The gae is to be in two diensions and viewed fro above. a) You decide to render a polygon with four sides with an iage of a spaceship texture apped onto it. The spaceship iage incorporates an alpha channel to be transparent around the edges of the spaceship. Show the code you would need in your display function to render the polygon with a texture ap on it. You should incorporate an approach to use the alpha channel in the iage to ensure the background is transparent and only the pixels related to the spaceship are rendered. (10 arks) b) Show with the aid of a diagra how you could copute if the spaceship collides with an asteroid using an approxiate circle-based approach. Describe how a regular grid ay be used to accelerate your approach. (8 arks) c) You would like your player to be able to shoot issiles at the asteroids. The issiles should ove in a straight line coing fro the front of the spaceship. Describe a procedure to fire a issile fro the spaceship position. Detail how you would calculate the next position for the issile as it travels. (6 arks) d) Soe of the asteroids are quite large and have quite varied polygon boundaries. Show how the Crossing Nuber Algorith could be used to copute when the tip of a issile hits one of the large asteroids. (8 arks) e) Explain how atrices and atrix stacks are used in OpenGL. Include in your answer the purpose of each of the following OpenGL coands. i) glpushmatrix (); ii) glpopmatrix (); iii) glloadidentity (); iv) glmatrixmode(gl_modelview); (8 arks)

3 -3-2. a) Assue you have a line segent defined between two points, A and B in two diensions, as shown in Figure 1. Detail how you could deterine which side of the line a third point, C, lies. Illustrate how your ethod works using the exaple shown in the diagra below. B(2,6) A(-1,3) C(3,4) Figure 1. (8 arks) b) In the context of fonts, describe what is eant by the ters Mono-spaced, Ligatures, Kerning and Optical Sizing. (8 arks) c) Describe, with the aid of diagras, what an outline font is and how it can be used. Detail the ain advantages of an outline font in coparison to a bitap font. (12 arks) d) The reshape function below should define the width of a window to be 20 units and the height to be 20 units with the origin in the centre. The OpenGL objects should be able to be displayed in any part of the window. void Reshape(int width, int height) { glviewport(?,?,?,?); glmatrixmode(gl_projection); glloadidentity(); gluortho2d(?,?,?,?); glmatrixmode(gl_modelview); glloadidentity(); } i) State what values should be used for the question arks. (4 arks) ii) State when the reshape function should be called and detail the purpose of the glmatrixmode coands in the reshape function. (6 arks) e) Briefly describe how double-buffering works (2 arks) PLEASE TURN OVER

4 -4-3. a) Answer all five questions below, each covering a selected topic fro the odule lectures. i) The 3D atrix for 2D transforations using hoogenous coordinates can be written in general as: Give the potential use(s) of each eleent ij in the above atrix with respect to translation, rotation and scaling. You can use nuerical exaples to illustrate your answer and draw corresponding figures illustrating the effect of your transforation on, for exaple, a square shape. (5 arks) ii) Briefly describe the HSV (Hue, Saturation and Value) colour odel by explaining each of H, S and V and label the on the 3D coordinate syste representing this odel. What is the advantage of the HSV odel over the RGB odel? (5 arks) iii) Illustrate the difference between 4- and 8-connectivity in a boundary filling algorith by drawing an arbitrary polygon. Which of the two is faster? (5 arks) iv) What are the advantages of the idpoint line drawing algorith over the DDA line drawing algorith? (5 arks) v) State all four scenarios and the action taken when processing vertices in sequence around the perieter of a polygon for the Sutherland-Hodgean polygon clipping algorith. (5 arks) (1)

5 -5- b) Iagine we start with a square at the origin as shown in Figure 2(a). We wish to derive the articulated geoetry (soe kind of robotic ar) as shown in Figure 2(b). Specify the 2D transforation atrices (in the correct order) to arrive at this geoetry by solely using three squares all starting in the origin as shown in Figure 2(a). Do this in three steps, i.e. first for the gantry, then the first link, then for the second link. (15 arks) y y 2s 2s 20º 45º s x 3s x (a) (b) Figure 2. PLEASE TURN OVER

6 -6-4. a) Consider the scan-line algorith for the polygon in Figure 3. i) Show the relevant scan lines on an updated figure (by copying Figure 3 into your answer booklet). Also indicate which points need to be lowered by drawing a dot underneath and label this new point with the pried label of the original point. (8 arks) ii) Deterine the initial bucket-sorted edge table using linked lists. (12 arks) E D C F A B Figure 3.

7 -7- b) Consider the Sutherland-Hodgean polygon clipping algorith for the polygon shown in Figure 4. Using the four clipping rules see Question 3 a) v.) clip the polygon for each of the four window edge processing stages, specifying the rules used and the vertex list after each stage. It is advised to use a four colun forat, i.e. window clipping edge, polygon edge evaluated, rule used and resulting edge, for each clipping stage. (20 arks) v 2 v 3 v 1 Figure 4. END OF PAPER