OpenGL screencast 4: drawing in 2D: triangles, quads, and polgyons

004.c

#include "screencasts.h"

/*  Globals */
double dim=2; /* dimension of orthogonal box */
char *windowName = "OpenGL screenscasts 4: Drawing triangles, quads, and polygons";
int windowWidth=500;
int windowHeight=500;

/*
 *  Display the scene
 */
void display()
{
  // used for GL_TRIANGLES example
  GLfloat verts[6][2]  = { {1.0,1.0}  ,{1.0,0.0} ,{0.0,1.0},
			   {-1.0,-1.0},{-1.0,0.0},{0.0,-1.0} };
  // used for GL_TRIANGLE_STRIP and GL_QUAD_STRIP example
  GLfloat verts2[6][2]  = { {-1.5,0.0},{-1.0,0.5},{-0.5,0.0},
			    {0.0,0.5}, {0.5,0.0}, {1.0,0.5} };
  // used for GL_TRIANGLE_FAN and GL_QUADS example
  GLfloat verts3[6][2]  = { {-1.5,-1.5},{-1.0,0.8},{-0.5,1.2},
			    {0.0,1.0},  {0.5,0.6}, {1.0,0.0} };
  // used for GL_QUADS example
  GLfloat verts4[8][2]  = { {-1.5,-1.5},{-1.5,0.0},{0.0,0.0},
			    {0.0,-1.0}, {0.3,0.0}, 
			    {1.0,0.0},  {1.0,1.0}, {0.4,0.8} };
  // used for GL_POLYGON example
  GLfloat verts5[6][2]  = { {0.0,-1.0}, {0.5,-0.8}, {0.5,0.5},
			    {0.0, 1.0}, {-0.5,0.8}, {-0.5,-0.5} };
			
  // White, Red, Green, Blue
  GLfloat colors[4][3] = { {1.0,1.0,1.0},{1.0,0.0,0.0},
			   {0.0,1.0,0.0},{0.0,0.0,1.0} };
  
  /*  Clear the image */
  glClear(GL_COLOR_BUFFER_BIT);
  /*  Reset previous transforms */
  glLoadIdentity();

  /*  Draw something here */
  // GL_TRIANGLES
  // 4 vertices - last one ignored
  /*
  glBegin(GL_TRIANGLES);
  glColor3fv( colors[0] );
  glVertex2fv( verts[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts[2] );
  glColor3fv( colors[3] );
  glVertex2fv( verts[3] );
  glEnd();
  */
  // 6 vertices
  /*
  glBegin(GL_TRIANGLES);
  glColor3fv( colors[0] );
  glVertex2fv( verts[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts[2] );

  glColor3fv( colors[0] );
  glVertex2fv( verts[3] );
  glColor3fv( colors[2] );
  glVertex2fv( verts[4] );
  glColor3fv( colors[3] );
  glVertex2fv( verts[5] );
  glEnd();
  */

  // GL_TRIANGLE_STRIP
  /*
  glBegin(GL_TRIANGLE_STRIP);
  glColor3fv( colors[0] );
  glVertex2fv( verts2[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts2[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts2[2] );
  glColor3fv( colors[0] );
  glVertex2fv( verts2[3] );
  glColor3fv( colors[1] );
  glVertex2fv( verts2[4] );
  glColor3fv( colors[3] );
  glVertex2fv( verts2[5] );
  glEnd();
  */
  // GL_TRIANGLE_FAN
  /*
  glBegin(GL_TRIANGLE_FAN);
  glColor3fv( colors[0] );
  glVertex2fv( verts3[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts3[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts3[2] );
  glColor3fv( colors[0] );
  glVertex2fv( verts3[3] );
  glColor3fv( colors[1] );
  glVertex2fv( verts3[4] );
  glColor3fv( colors[3] );
  glVertex2fv( verts3[5] );
  glEnd();
  */
  // GL_QUADS
  // 6 vertices - last two ignored
  /*
  glBegin(GL_QUADS);
  glColor3fv( colors[0] );
  glVertex2fv( verts3[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts3[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts3[2] );
  glColor3fv( colors[3] );
  glVertex2fv( verts3[3] );
  glColor3fv( colors[1] );
  glVertex2fv( verts3[4] );
  glColor3fv( colors[3] );
  glVertex2fv( verts3[5] );
  glEnd();
  */
  // 8 vertices
  /*
  glBegin(GL_QUADS);
  glColor3fv( colors[0] );
  glVertex2fv( verts4[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts4[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts4[2] );
  glColor3fv( colors[3] );
  glVertex2fv( verts4[3] );
  glColor3fv( colors[0] );
  glVertex2fv( verts4[4] );
  glColor3fv( colors[1] );
  glVertex2fv( verts4[5] );
  glColor3fv( colors[2] );
  glVertex2fv( verts4[6] );
  glColor3fv( colors[3] );
  glVertex2fv( verts4[7] );
  glEnd();
  */
  // GL_QUAD_STRIP
  /*
  glBegin(GL_QUAD_STRIP);
  glColor3fv( colors[0] );
  glVertex2fv( verts2[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts2[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts2[2] );
  glColor3fv( colors[0] );
  glVertex2fv( verts2[3] );
  glColor3fv( colors[1] );
  glVertex2fv( verts2[4] );
  glColor3fv( colors[3] );
  glVertex2fv( verts2[5] );
  glEnd();
  */
  // GL_POLYGON
  glBegin(GL_POLYGON);
  glColor3fv( colors[0] );
  glVertex2fv( verts5[0] );
  glColor3fv( colors[1] );
  glVertex2fv( verts5[1] );
  glColor3fv( colors[2] );
  glVertex2fv( verts5[2] );
  glColor3fv( colors[3] );
  glVertex2fv( verts5[3] );
  glColor3fv( colors[0] );
  glVertex2fv( verts5[4] );
  glColor3fv( colors[1] );
  glVertex2fv( verts5[5] );
  glEnd();

  /*  Flush and swap */
  glFlush();
  glutSwapBuffers();
}

/*
 *  GLUT calls this routine when the window is resized
 */
void reshape(int width,int height)
{
  double w2h = (height>0) ? (double)width/height : 1;
  glViewport(0,0, width,height);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-dim*w2h,+dim*w2h, -dim,+dim, -dim,+dim);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

/*
 *  windowKey
 *  ------
 *  GLUT calls this routine when a non-special key is pressed
 */
void windowKey(unsigned char key,int x,int y)
{
  /*  Exit on ESC */
  if (key == 27) exit(0);
}

/*
 *  Start up GLUT and tell it what to do
 */
int main(int argc,char* argv[])
{
  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
  glutInitWindowSize(windowWidth,windowHeight);
  glutCreateWindow(windowName);

  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutKeyboardFunc(windowKey);

  glutMainLoop();
  return 0;
}