OpenGL hands-on tutorial

Legacy OpenGL

Create the following first.c using your favourite editor.

#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.

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

make
./first

Try the same program in 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

python first.py

Exercise #1:

1. Add RGB color to vertices with glColor3f(0.0, 0.4, 1.0);.
2. Replace single line drawing in display() with the following snippet

      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.
4. Add different color to each vertex.

    GLfloat color[][3] = {
     {1, 0, 0}, {0, 1, 0}, {0, 0, 1},
     {1, 1, 0}, {0, 1, 1}, {1, 0, 1}};
   

5. Replace loop with the following

     glVertexPointer(2, GL_FLOAT, 0, &vertices[0][0]);
     glEnableClientState(GL_VERTEX_ARRAY);
     glDrawArrays(GL_TRIANGLES, 0, 6);
     glDisableClientState(GL_VERTEX_ARRAY);
   

   How can we add color to vertices? See ​glColorPointer and