#include <stdio.h>
#include <GL/glut.h>

void reshape(int w, int h)
{
  glViewport(0, 0, w, h);      
  glMatrixMode(GL_PROJECTION); 
  glLoadIdentity();            
  glOrtho(0, w, 0, h, -1, 1);  
  glScalef(1, 1, 1);         
  glTranslatef(w/2, h/2, 0);     
}

double b1[100][2], b2[100][2];
int n, a;

void load_data(){

	FILE *infile;
	char filename[20];
	int i;

	printf("Enter the name of the first file:\n> ");
	scanf("%s", &filename);
	infile = fopen(filename, "r");
	fscanf(infile, "%d", &n);
	for(i=0;i<n;i++)
		fscanf(infile, "%lf%lf", &b1[i][0], &b1[i][1]);
	fclose(infile);
	
	printf("Enter the name of the second file:\n> ");
	scanf("%s", &filename);
	infile = fopen(filename, "r");
	fscanf(infile, "%d", &n);
	for(i=0;i<n;i++)
		fscanf(infile, "%lf%lf", &b2[i][0], &b2[i][1]);
	fclose(infile);
}

void bezier(double b[][2], double u, double p[]){

	double p11[2], p21[2], p31[2], p22[2], p32[2];
	int i;

	for(i=0; i<2; i++){
		p11[i] = (b[1][i]*u)+(b[0][i]*(1.0-u));
		p21[i] = (b[2][i]*u)+(b[1][i]*(1.0-u));
		p31[i] = (b[3][i]*u)+(b[2][i]*(1.0-u));
		p22[i] = (p21[i]*u)+(p11[i]*(1.0-u));
		p32[i] = (p31[i]*u)+(p21[i]*(1.0-u));
		p[i] = (p32[i]*u)+(p22[i]*(1.0-u));
	}
}

void draw_curve(double b[][2]){

	double p[3], u;
	int i, j;

  glClear(GL_COLOR_BUFFER_BIT);
  glBegin(GL_LINE_STRIP);
    glColor3f(1.0, 0.0, 0.0); 
    	for(j=0; j<n; j+=4){
		for(i=0; i<20; i++){
			u=(float)i/20.0;
			bezier(b+j,u,p);
			glVertex2f(p[0], p[1]);
		}
	}
  glEnd();
  glFlush();
}

void step(double b[][2]){

	int i, j;

	for(j=0; j<n; j++)
		for(i=0; i<2; i++)
			b[j][i] = b1[j][i] + (b2[j][i]-b1[j][i])*((float)a)/20.0;
	a++;
}

void display(void)
{
  double b[100][2];
  int i;

  a=0;

  while(a<20){
    for(i=0;i<1000000;i++)
      ;
    step(b);
    draw_curve(b);
  }
}

void keyboard(unsigned char key, int x, int y){

  switch (key){
  case 27:
    exit(0);
    break;
  case ' ':
    glutPostRedisplay();
    break;
  }
}

int main(int argc, char **argv)
{

  load_data();
  glutInit(&argc, argv);
  glutCreateWindow("single triangle");
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutKeyboardFunc(keyboard);
  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}