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# Homework 1: Read and Draw a 3D Surface Mesh solution

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Homework 1: Read and Draw a 3D Surface Mesh
Write an OpenGL program to read and display a 3D mesh (in .obj format).
1. Write a function, “bool ReadOBJFile(const char filename[])”, to
read in an obj file and store the elements into a vertex list and face list.
2. Implement a “ComputeBoundingBox()” function, to compute the
bounding box of the object, its diagonal axis length, and its center, then
put the camera at:
x_cam = x_BCenter;
y_cam = y_BCenter;

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## Description

Homework 1: Read and Draw a 3D Surface Mesh
Write an OpenGL program to read and display a 3D mesh (in .obj format).
1. Write a function, “bool ReadOBJFile(const char filename[])”, to
read in an obj file and store the elements into a vertex list and face list.
2. Implement a “ComputeBoundingBox()” function, to compute the
bounding box of the object, its diagonal axis length, and its center, then
put the camera at:
x_cam = x_BCenter;
y_cam = y_BCenter;
z_cam = z_BCenter + 1.5 *BDiagonalAxisLength;
and look towards the bounding box center (x_BCenter, y_BCenter,
z_BCenter).
3. Implement the “Render_Mesh()” function to finish the OpenGL rendering.
(See next page).
4. Follow “Ex8.cpp” to perform keyboard + mouse-controlled rotation (R,
mouse left button), panning (T, mouse left button), and zooming (Z, mouse
left button) functions.
Note 1: Please write all you codes in one “hw1.cpp” file. Test and make sure it
compiles and renders correctly, then upload your “hw1.cpp” file only. I will
compile and run it on my computer to see your result.
Note 2: You only need to consider the simplest OBJ format in this homework.
It contains a list of vertices (each row starts with a keyword “v”, e.g., v x y z),
and a list of faces (each row starts with a keyword “f”, e.g., f vInd1 vInd2
vInd3). Note that the vertex index vInd starts at 1. So if you have store vertex
positions in an array, the first vertex is at position 0, and each vertex’s
location is vInd-1.
The homework is due: 11:59pm, Feb. 10th.
If you are late for x days, each one more day you get 5% off. Namely, your
homework score will be calculated as: (the score based on your codes) * (0.95^x)
Computing Bounding Box (BB) of a 3D object
A bounding box (BB) of an object is defined as a minimal coordinate-axis-aligned
box that completely contains this object.
BB can be simply defined by the minimal and maximal x, y, and z coordinate
values of the objects’ vertices: ?? = [????, ????] × [????, ????] × [????, ????]
The center of a BB can be simply defined as the
???????? =
????+????
2
; ???????? =
????+????
2
; ???????? = (???? + ????)/2
The diagonal axis length of a BB roughly measures the size of the object:
? = √(???? − ????)
2 + (???? − ????)
2 + (???? − ????)
2
Rendering a Triangle Mesh
Each triangle mesh contains a list of faces. Each face ? has three points
(??
, ??
, ??) where each point ?? has three coordinates (??
, ??
, ??) .
Therefore, you can implement Render_Mesh() based on the following
pseudo-code:
glBegin(GL_TRIANGLES);
//Let F denote the total number of faces
for (int ind=0; ind< F; ++ind) {
let ? be the ???-th face;
get ?’s three points ??
, ??
, ?? using their vertex indices;
get ??
’s coordinates (??
, ??
, ??
); same for ?? and ??
glVertex3f(??
, ??
, ??
);
glVertex3f(??
, ??
, ??
);
glVertex3f(??, ??, ??);
}
glEnd();