#include "zoom.h"
#include "../callbacks/reshape.h"
#include "../../util/check_error.h"
#include "../../view/state0.h"
#include <GL/glut.h>
#include <math.h>

/*
 * A simple alias to make the code more readable.
 */
#define S state0

void
zoom (double x1, double y1, double x2, double y2)
{
  S.zoom.active = true;

  S.zoom.coords[0] = x1;
  S.zoom.coords[1] = x2;
  S.zoom.coords[2] = y1;
  S.zoom.coords[3] = y2;

  /*
   * Preserve the aspect ratio.  First convert the selection to the
   * aspect ratio of the original geometry. The world is a square so
   * convert the zoom region to a square. The reshape callback
   * performs step two of converting the squarified zoom region to the
   * aspect ratio of the window. This is done in reshape as the window
   * may change while the zoom region is held the same.
   */
  double width = S.zoom.coords[1] - S.zoom.coords[0];
  double height = S.zoom.coords[3] - S.zoom.coords[2];
  double difference = fabs (width - height);

  if (width > height)
    {
      S.zoom.coords[2] -= 0.5 * difference;
      S.zoom.coords[3] += 0.5 * difference;
    }
  else
    {
      S.zoom.coords[0] -= 0.5 * difference;
      S.zoom.coords[1] += 0.5 * difference;
    }

  GLint viewport[4];
  glGetIntegerv (GL_VIEWPORT, viewport);
  reshape (viewport[2], viewport[3]);

  glutPostRedisplay ();

  return;
}