CENG Assignment 3 - A Software Rasterizer using OpenGL Solution

    • Objectives

In this assignment, you are going to implement an OpenGL program to render a given scene. The input les for this assignment are very similar to the ones in the rst two assignments. A number of point light sources will be provided in the scene le. A number of material properties will be de ned and assigned to triangular mesh models. The scene will be rendered using the built-in OpenGL illumination model and the smooth shading mode. The parameters of a perspective view camera are also speci ed in the input. You will perform modeling transformations to triangular mesh models.


Keywords: OpenGL,  xed pipeline, modeling transformations, viewing transformations


    • Speci cations

        1. The name of the executable will be \hw3".

        2. Your executable will take an XML le name from command line. Input le names are not static, they can be anything. XML le has minor di erences from rst and second assignments. It has only one camera and Transformations tag. The only object type included in this homework is Mesh.

        3. You will be given a sample make le. You can extend it or use as it is. However, be sure, before submitting, it is running on Inek machines. The executable should be run with the "./hw3 sample input.xml" command smoothly. It will not produce any outputs since an OpenGL display window will be used.

        4. You can use \X11 forwarding" to work on Inek machines. To do so, you need to rst connect to login.ceng.metu.edu.tr (not external.ceng.metu.edu.tr) through ssh with -X ag. After you reached the login lobby machine, you need to connect to any of the inek machines with -X ag.



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    5. You will compute normal vectors of vertices as the average of the normal vectors of the triangles incident to this vertex.

    6. The scene will only be composed of instances of triangles. With a sequence of several trans-formations (translation, rotation, scaling) you will be able to move, rotate, or resize a model (i.e., all of the triangles in the model). Transformations will be applied to the models in the order speci ed in the input le. You may use OpenGL functions to transform your models.

    7. Models will be rendered in solid or wireframe modes as speci ed in the input le. Use the OpenGL function call glPolygonMode(GL FRONT AND BACK, GL FILL); for the solid and the call glPolygonMode(GL FRONT AND BACK, GL LINE); for the wireframe modes, respectively.

    8. You will not compute lightings explicitly. It will be done automatically by calling appropriate OpenGL functions.

    9. In both wireframe and solid modes, triangles whose backface or frontface to the viewer will be culled according to the parameter in the input le. Backface/frontface culling should be en-abled/disabled according to the setting in input le. CullingEnabled can be 0 (disabled) or 1 (enabled) and CullingFace can be 0 (backface) or 1 (frontface).

    10. Use the smooth shading mode of OpenGL by calling the function glShadeModel(GL SMOOTH);.

    11. To specify the location/parameters of camera, you may use gluPerspective function.

    12. You will show the FPS (frame-per-second) in the title. The title will look like to the one in the sample image.

    13. Helper functions for reading inputs are given to you. It is STRONGLY recommended to inspect types in header les and helper functions, which are given to you in homework stub code.



























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    • Sample input/output

Sample input les are given at COW. The initial view of the OpenGL display window for the horse and mug input is shown in the image below where the horse is rendered as a lled mesh whereas the mug is rendered as wireframe.





























    • Hints & Tips

        1. Start early!

        2. When lighting is enabled, OpenGL does not use glColor to color the surfaces by default. Instead, surface material properties are de ned using the glMaterialfv function. To set the color of surface (or the entire model), use the following piece of code just before drawing the

object.

GLfloat
ambColor [ 4 ]
= f<ar >, <ag >, <ab >,
1 . 0 g ;
GLfloat
diffColor [ 4 ]
= f<dr >, <dg >, <db >,
1 . 0 g ;
GLfloat
specColor [ 4 ]
= f<sr >, <sg >, <sb >,
1 . 0 g ;
GLfloat
specExp [ 1 ]  = f<specular  exponent >g;

glMaterialfv ( GL_FRONT , GL_AMBIENT , ambColor ) ; glMaterialfv ( GL_FRONT , GL_DIFFUSE , diffColor ) ; glMaterialfv ( GL_FRONT , GL_SPECULAR , specColor ) ; glMaterialfv ( GL_FRONT , GL_SHININESS , specExp ) ;

Finally, to determine the amount of light re ected from the surfaces correctly, you should specify the normal vectors of the vertices.





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    • Regulations

        1. Programming Language: C++

        2. Late Submission: Refer to the syllabus for the late policy.

        3. Groups: You can team-up with another student. But you must notify the assistants about who your partner is within the allowed time frame.

        4. Cheating: We have zero tolerance policy for cheating. People involved in cheating will be punished according to the university regulations and will get 0 from the homework. You can discuss algorithmic choices, but sharing code between groups or using third party code is strictly forbidden. To prevent cheating in this homework, we also compare your codes with online ray tracers and previous years’ student solutions. In case a match is found, this will also be considered as cheating. Even if you take only a \part" of the code from somewhere or somebody else, this is also cheating. Please be aware that there are \very advanced tools" that detect if two codes are similar.

        5. Newsgroup: You must follow the ODTUCLASS forum for discussions, possible updates, and corrections.

        6. Submission: Submission will be done via ODTUCLASS. Create a \tar.gz" le that contains all your source code les and a make le. The executable should be named as \hw3" and should be able to be run using the command \./hw3 scene le name.xml". The .tar.gz le name should be:

            ▪ If a student works with a partner student:

<partner_1_student_id>_<partner_2_student_id>_hw3.tar.gz


            ▪ If a student works alone: <student_id>_hw3.tar.gz

            ▪ For example:


1234567_2345678_hw3.tar.gz

1234567_hw3.tar.gz


    7. Evaluation: Your codes will be evaluated on Inek Machines; based on several input les including, but not limited to the test cases given to you as examples. Evaluation will be done manually, small di erences might be tolerated.










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