Assessment Preview - This is an example student view of this assessment done Exam 2 Part 1 of 5 - Modern Graphics Pipeline Question 1 of 27 Match each stage in the graphics pipeline with a description of the operations generally performed therein. A. generate new vertices and primitives, subdivide surface dynamically B. matrix transformations (projection, camera, object), flat or smooth shading, clipping C. z-buffer algorithm, interpolating normal vectors, viewport transform D. creation of base geometry, definition of lighting properties, animation E. compositing, per-pixel shading, texture mapping 1. vertex 2. fragment 3. rasterizer 4. geometry 5. application Question 2 of 27 Which of the stages from the prior question are programmable in the modern pipeline? A. all of them B. only the application stage C. vertex, rasterizer, and fragment D. all except the rasterizer Question 3 of 27 Gouraud smooth shading is performed at the stage of the pipeline, while Phong shading is done at the stage. Question 4 of 27 1 of 10 12/07/2010 06:18 PM
Consider the image above. Following the Cohen-Sutherland algorithm, the outcodes for endpoints a and b are and, respectively. Question 5 of 27 Can we trivially accept/reject the line segment in the prior question? Explain your answer. Part 2 of 5 - Lighting & Shading Question 6 of 27 Match each type of reflection with the appropriate heuristic formula. Use accompanying diagram to jog you memory. 2 of 10 12/07/2010 06:18 PM
A. k * I B. k * I * max(0, n l) C. k * I * max(0, r v) p 1. diffuse reflection 2. specular reflection 3. ambient reflection Question 7 of 27 Derive a complete reflection model for multiple lights incorporating each of the formulæ from the prior question. Question 8 of 27 What do the k, I, and p scalars represent, respectively, in the above formulæ? Question 9 of 27 Smooth shading differs from flat shading in that: A. colors are blended across the surface using a texture map B. it requires programmable geometry shaders C. the underlying surface geometry is subdivided to yield finer detail D. lighting is computing multiple times per primitive using vertex normals Question 10 of 27 For Phong shading, the lighting equation must be evaluated once for each of the rasterized primitive. Gouraud shading is more efficient because the lighting equation must be evaluated once per. 3 of 10 12/07/2010 06:18 PM
Question 11 of 27 If, upon rendering, one object (but not the whole scene) appears completely black and featureless, which of the following is the most common, plausible explanation? A. there are no active lights in the scene B. the alpha color component is accidentally set to zero C. it is obscured by another, closer object D. the surface normal vectors are inverted (pointing inward) Question 12 of 27 Briefly explain the "infinite light" and "infinite viewer" optimizations. Part 3 of 5 - Texture Mapping Question 13 of 27 For each of the following objects or effects, indicate whether it would be best modeled using image-based (I) textures, or procedural (P) textures. decal or logo stone clouds surface of Earth fabric wood Question 14 of 27 Briefly discuss the relative advantages and disadvantages using of procedural versus image-based textures. Address issues such as time/memory efficiency and visual artifacts of the texture-mapping process. 4 of 10 12/07/2010 06:18 PM
Question 15 of 27 Bump mapping is a technique used to simulate small-scale surface features without the need for detailed geometric models. The effect is achieved by: A. changing the color at each point based on the nearest texel in the texture image B. moving the position of each vertex by some random small amount C. recalculating the lighting for each point using a slightly different position for the light source D. perturbing the normal vector at each point based on the associated texel value Question 16 of 27 A tell-tale artifact of the bump mapping technique is that the object's expensive approach that does affect the actual shape of the object is called will appear unchanged. A more mapping. Question 17 of 27 Consider the texture image above. For each possible mapping to a quad face shown below, specify the normalized UV texture coordinates of the lower right-hand vertex. Assume that texture coordinates (0,0) and (0,1) map to the upper and lower left-hand corners of the image, respectively. Furthermore, the texture function wraps horizontally and vertically, so that (2,0) maps to the same color as (1,0). 5 of 10 12/07/2010 06:18 PM
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3., ) ( Part 4 of 5 - Graphics Data Structures Question 18 of 27 4.0 Points Consider the following description of a (possibly animated) 3D scene. Then draw a plausible scene graph for this scene, being sure to consider how various elements may be positioned or animated. Note: You may create your scene graph in an editor, save the file and then upload; alternatively, you can simply sketch the graph by hand on paper and submit the hard-copy at the conclusion of the exam. "A small cottage has a two windows that each may open by sliding up/down, a hinged front door that can swing open. On the door is a knob that can turn in the usual way." Upload File: Browse... Question 19 of 27 Scene graphs offer many opportunities for optimization. One method discussed in class, known as instancing, involves taking advantage of similar/identical geometry in order to reduce memory requirements. Explain how using this method would change the scene graph you sketched for the previous question; or, if you accounted for this technique in your graph, explain where. 7 of 10 12/07/2010 06:18 PM
Question 20 of 27 Briefly explain how animation is achieved when using a scene graph. (Hint: Recall the various types of graph traversal used by OSG.) Question 21 of 27 Shared-vertex representations such as triangle strips or fans can be useful for some applications, but not so much for others. Select the explanation below that best characterizes why. A. they require too much memory for certain mesh topologies B. they are useful in C-programs but are difficult to implement in an object-oriented design C. they are extremely slow to traverse for large meshes D. they are storage efficient but are not conducive to editing Question 22 of 27 Explain what data we store in a Half-Edge data structure and why this is a more time-efficient representation, for traversal, than the traditional Winged-Edge. You may refer to the diagram of a Winged-Edge below to jog your memory. 8 of 10 12/07/2010 06:18 PM
Question 23 of 27 Complete the following pseudo-code for the EdgesOfVertex routine. EdgesOfVertex (v) let e = do.edge if (v == e. ) e = e.leftnext else e = e. while (!= v.e) Question 24 of 27 3.0 Points Complete the tables below, given the above diagram of a triangle mesh. Note that uppercase letters indicate Vertices, lowercase letters indicate Edges, and digits indicate Faces. WingedEdge Table Edge Head Tail Vertex Vertex Left Face a A B 2 0 f Right Face Left Prev b A c D A 2 1 a d B C 3 0 h e f D B g E B 3 5 d h C i D E 4 5 h Vertex Table Vertex Edge A b 9 of 10 12/07/2010 06:18 PM
B C D e i E Face Table Face Edge 0 a 1 c 2 3 g 4 5 i Part 5 of 5 - Antialiasing & Compositing Question 25 of 27 Complete the formula for basic alpha compositing. Type cf to indicate the foreground color, and cb to indicate the background color. c = α * + ( - α) * Question 26 of 27 Briefly explain how resampling is used to implement antialiasing in each of the following algorithms: rasterization, ray-tracing, and texturemapping. Specifically, describe differences in what we are sampling. Question 27 of 27 Which of the following describes what mipmaps are? A. a subtree within a scene graph hierarchy B. images used to make a surface appear bumpy C. a function used to match 3D world coordinates to 2D texture coordinates D. smaller resolution versions of an image used for blending or LOD Assessment Preview - This is an example student view of this assessment done 10 of 10 12/07/2010 06:18 PM