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1. |
Create a new source file. File
--> New... --> Files Tab --> C++ Source File
--> Name the file as "main" at File_name.
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2. |
Here is the first program.
Copy it into "main.cpp" file (only the program).
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3. |
Click Build --> Compile main.cpp -->
Build <project name>.exe --> Execute <project
name>.exe.
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4. |
Now if there is no error generated, you
should be able to see this:
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5. |
Now, we will have a code walkthrough on
what is happening inside the program.
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6. |
Line 1 to 5 is the comment. Use it to
write the programmer's name, program's name and date.
//===============================================//
// Title : First OpenGL Program
// Programmer : V R E M P I R E
// Date : Thursday, July 12, 2001
//===============================================// |
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7.
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Line 8 is used to call the GLUT
library. When glut.h is called, it will automatically call gl.h
and glu.h.
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8.
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Now we go inside main function at line
37. At line 39, glutInit is used to initialize GLUT library
inside our window system so they can talk with each other.
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9.
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At line 40, glutInitDisplayMode
is used to set the initial display mode.
| glutInitDisplayMode(GLUT_DOUBLE
| GLUT_RGB); |
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10.
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At line 41, glutInitWindowSize
is used to set the initial window size based on pixel unit.
| glutInitWindowSize(400,
400); |
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11.
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At line 42, glutInitWindowPosition
is used to set the initial window position based on X and Y value
of our window system.
| glutInitWindowPosition(200,
200); |
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12.
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At line 43, glutCreateWindow is
used to create a top level window. The value inside the function
will be used as the title on the top-left of the window.
| glutCreateWindow("First
OpenGL Program"); |
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13.
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At line 44, Init() function is called.
At line 24 in the Init() function, the glClearColor command is
called. glClearColor will specify clear values for the color
buffers. This will give the color of the window. The first
parameter is for Red, second is for Green and the third one
is for Blue. The value of each of them is between 0.0 and 1.0.
| glClearColor(0.0,
0.0, 0.0, 0.0); |
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14.
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At line 45, glutDisplayFunc is
used to set the display callback for the current window. Here, it
will call the function Display() at line 10.
| glutDisplayFunc(Display); |
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15.
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At line 12, glClear is
used to clear buffers to preset values.
| glClear(GL_COLOR_BUFFER_BIT
| GL_DEPTH_BUFFER_BIT); |
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16.
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At line 13, glLoadIdentity is
used to replace the current matrix with the identity matrix.
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17.
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At line 14, gluLookAt is
used to define a viewing transformation. The first three
parameters is the x, y and z coordinate of our eye in the
3-dimensional world. The next three parameters is the x, y and z
coordinate of the Center Of Interest. The next three parameters is
the up vector.
| gluLookAt(0.0,
0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0); |
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18.
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At line 15, glColor3f is
used to set a new three-valued RGB color. First value is Red,
second is Green and the third one is Blue.
| glColor3f(0.0,
1.0, 0.0); |
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19.
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At line 17, glutSolidCube is
used to render a solid cube.
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20.
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At line 19, glutSwapBuffers is
used to swaps the buffers of the current window if double
buffered. This function will automatically called glFlush
to clear back the buffers.
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21.
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At line 46, glutReshapeFunc is
used to set the reshape callback for the current window. Here, it
will call the function Resize() at line 27.
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22.
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At line 29, glViewport is
used to specify the affine transformation of x and y from
normalized devices coordinates to window coordinates.
| glViewport(0,
0, width, height); |
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23.
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At line 30, glMatrixMode is
used to specify which matrix is the current matrix. GL_PROJECTION
is used to tell the matrix that currently it is for projection.
| glMatrixMode(GL_PROJECTION); |
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24.
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At line 31, glLoadIdentity is
used to refresh the matrix.
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25.
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At line 32, gluPerspective is
used to
set up a
perspective projection matrix. It specifies a viewing frustum into
the world coordinate system. First parameter is the degrees for
our eye to see in y-axis. The second parameter is the aspect
ratio. The third parameter is distance from our eye to nearest
z-plane. The fourth parameter is the distance from our eye to the
farthest z-plane.
| gluPerspective(60.0,
width/height, 0.1, 1000.0); |
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26.
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At line 33, glMatrixMode is
used to specify which matrix is the current matrix. GL_MODELVIEW
is used to tell the matrix that currently it is used to display
model.
| glMatrixMode(GL_MODELVIEW); |
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27.
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At line 47, glutMainLoop is
used to
enters the GLUT event processing loop.
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28.
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I think that's all for now for the
beginning. Let's move to the next chapter on how to create our own
polygon, instead of using GLUT default polygon.
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