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= OpenGL hands-on tutorial =


== Legacy OpenGL ==
Create the following {{{first.c}}} using your favourite editor.
{{{
#!c
#include <GL/glut.h>

void display()
{
  glClear(GL_COLOR_BUFFER_BIT);
  glColor3f(1.0, 0.4, 1.0);
  glBegin(GL_LINES);
    glVertex2f(0.1, 0.1);
    glVertex3f(0.8, 0.8, 1.0);
  glEnd();
  glutSwapBuffers();
}

int main(int argc, char *argv[])
{
  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_DOUBLE);
  glutCreateWindow("first.c GL code");
  glutDisplayFunc(display);
  glutMainLoop();
  return 0;
}
}}}

Create {{{Makefile}}} to build your program.

{{{
#!sh
CFLAGS=-Wall
LDFLAGS=-lGL -lGLU -lglut -lGLEW

ALL=first
default: $(ALL)

first : first.o

clean:
      rm -rf *~ *.o $(ALL)
}}}
Beware that Makefile is TAB aware. So the last line should contain TAB indentation and not spacing.

Make and run the program with
{{{
#!sh
make
./first
}}}

Try the same program in Python
{{{
#!python
from OpenGL.GLUT import *
from OpenGL.GL import *
import sys

def display():
    glClear(GL_COLOR_BUFFER_BIT)
    glColor3f(1.0, 0.4, 1.0)
    glBegin(GL_LINES)
    glVertex2f(0.1, 0.1)
    glVertex3f(0.8, 0.8, 1.0)
    glEnd()
    glutSwapBuffers()

if __name__ == "__main__":
    glutInit(sys.argv)
    glutInitDisplayMode(GLUT_DOUBLE)
    glutCreateWindow("first.py GL code")
    glutDisplayFunc(display)
    glutMainLoop()
}}}
and run it with 
{{{
#!sh
python first.py
}}}


=== Exercise #1: ===
 1. Add RGB color to vertices with {{{ glColor3f(1.0, 0.4, 1.0);}}}.
 2. Replace single line drawing in {{{display}}} with the following snippet
 {{{
#!c
   GLfloat vertices[][2] = {
    { -0.90, -0.90 }, // Triangle 1
    {  0.85, -0.90 },
    { -0.90,  0.85 },
    {  0.90, -0.85 }, // Triangle 2
    {  0.90,  0.90 },
    { -0.85,  0.90 }
   };
}}}
 and try to draw two wireframe triangles in a loop. Change primitive to {{{GL_LINE_LOOP}}}.
 3. Draw two primitives with {{{GL_TRIANGLES}}}.