curve3.c Example C Language Program

/*
Example: curve3.c

This program draw a Bezier curve segment using curveit().  The
Cardinal spline and B-spline curve segments could be drawn in a
similar manner (only the basis matrix would be different).
*/

#include <gl/gl.h>
#include <gl/device.h>

#define BEZIER 1

Matrix beziermatrix = {
  { -1.0,  3.0, -3.0,  1.0 } ,
  {  3.0, -6.0,  3.0,  0.0 },
  { -3.0,  3.0,  0.0,  0.0 },
  {  1.0,  0.0,  0.0,  0.0 }};

Matrix geom1 = {
  { 50.0, 150.0, 0.0, 1.0},
  { 150.0, 225.0, 0.0, 1.0},
  { 150.0, 075.0, 0.0, 1.0},
  { 250.0, 150.0, 0.0, 1.0}};

Matrix precisionmatrix = {
  { 6.0/8000.0,       0.0,    0.0, 0.0},
  { 6.0/8000.0, 2.0/400.0,    0.0, 0.0},
  { 1.0/8000.0, 1.0/400.0, 1/20.0, 0.0},
  {        0.0,       0.0,    0.0, 1.0}};

main()
{    
  int dev,val;    

  initialize();    

  while (TRUE) {        
    if (qtest()) {            
      dev = qread(&val);            
      if (dev == ESCKEY) {
        gexit();
        exit();
      }
      else if (dev == REDRAW) {
        reshapeviewport();
        drawcurve();
      }
    }
  }

}

initialize()
{    
  int gid;    

  prefposition(200, 500, 100, 400);
  gid = winopen("curve3");    
   winconstraints();
  qdevice(ESCKEY);
  qdevice(REDRAW);
  qenter(REDRAW,gid);
}

drawcurve()
{    
  int i,xx,yy;

  color(BLACK);
  clear();
  pushmatrix();                /* the current transformation 
                                * matrix on the matrix stack is 
                                * saved */

  multmatrix(geom1);           /* the product of the current 
                                * transformation matrix and the 
                                * matrix containing the 
                                * control points becomes the new 
                                * current transformation matrix */

  multmatrix(beziermatrix);    /* the product of the basis 
                                * matrix and the current 
                                * transformation matrix becomes 
                                * the new current transformation 
                                * matrix */

  multmatrix(precisionmatrix); /* the product of the precision 
                                * matrix and the current 
                                * transformation matrix 
                                * becomes the new current 
                                * transformation matrix */

  move(0.0,0.0,0.0);           /* this command must be issued 
                                * so that the correct first 
                                * point is generated by the 
                                * curveit command */

  color(RED);
  curveit(20);                 /* a curve consisting of 20 line 
                                * segments is drawn */

  popmatrix();                 /* the original transformation 
                                * matrix is restored */

    /* show the control points */
  color(WHITE);
  for ( i = 0 ; i < 4 ; i++ )  {
    for ( xx = -2 ; xx < 2 ; xx++) {
      for ( yy = -2 ; yy < 2 ; yy++) {
        pnt2( geom1[i][0] + (Coord) xx , geom1[i][1] + (Coord) yy);
      }
    }
  }

}

/*
  Changes: 
    - the control points are drawn on the screen
    - added winconstraints() so the window could be resized
    - changes the geometry so it would be centered
      from:
         Matrix geom1 = {
            { 100.0, 100.0, 0.0, 1.0},
            { 200.0, 200.0, 0.0, 1.0},
            { 200.0,   0.0, 0.0, 1.0},
            { 300.0, 100.0, 0.0, 1.0}};
      to:
         Matrix geom1 = {
            { 100.0, 150.0, 0.0, 1.0},
            { 200.0, 225.0, 0.0, 1.0},
            { 200.0, 075.0, 0.0, 1.0},
            { 300.0, 150.0, 0.0, 1.0}};
*/

Related Information

The curveit subroutine, the multmatrix subroutine.

Drawing Curves in GL3.2 Version 4 for AIX: Programming Concepts.