/**
  * SimpleCamera implements the simple camera where the VPN is along
  * -Z, VUV is Y and the COP is on Z. A viewport is specified on
  * the XY plane.
  *
  * @author Anthony Steed
  * @version 1.0
  */

public class SimpleCamera {
  
  /*
   * Hold the dimensions of the viewport
   */
  private double Xmin, Xmax, Ymin, Ymax;

  /* 
   * Hold the resolution of rays to cast
   */
  private int xResolution, yResolution; 

  /* 
   * Centre of projection along z-axis
   */
  private double Zcop;
    
  /* 
   * Hold the ray pitch and offset for centre of first pixel
   */
  private double Width, Height, Wo2, Ho2; 
    
  /**
    * Create a basic camera with resolution of 100 by 100
    */
  public SimpleCamera() {
    initBasic(100,100);
  }

  /**
    * Create a basic camera with given resolution
    * @param x the number of rays across
    * @param y the number of rays down
    */
  public SimpleCamera(int x, int y) {
    initBasic(x,y);
  }

  /*
   * Create the basic camera
   */
  protected void initBasic(int x, int y) {
    xResolution = x;
    yResolution = y;
    Zcop = 1.0;
    setVPWindow(-1.0,1.0,-1.0,1.0);
  }

  /**
    * Set the viewport window on the XY plane
    * @param xmin the minimum x value
    * @param xmax the maximum x value
    * @param ymin the minimum y value
    * @param ymax the maximum y value
    */
  public void setVPWindow(double xmin, double xmax, double ymin, double ymax) {
    Xmin = xmin;
    Xmax = xmax;
    Ymin = ymin;
    Ymax = ymax;
    Width = (Xmax-Xmin)/(double)xResolution;
    Wo2 = Width/2.0;
    Height = (Ymax-Ymin)/(double)yResolution;
    Ho2 = Height/2.0;
  }

  /**
    * Set the centre of projection on the Z axis
    * @param cop the COP z value
    */
  public void setCOP(double cop) {
    Zcop = cop;
  }

  /**
    * Set the resolution of the camera in terms of the number of rays
    * to cast.
    * @param x the number of rays across
    * @param y the number of rays down
    */
  public void setResolution(int x, int y) {
    xResolution = x;
    yResolution = y;
    Width = (Xmax-Xmin)/(double)xResolution;
    Wo2 = Width/2.0;
    Height = (Ymax-Ymin)/(double)xResolution;
    Ho2 = Height/2.0;
  }


  /**
    * Get the ray number i, j from the camera model
    * @param i the x index of the ray to create
    * @param j the y index of the ray to create
    * @return a new ray as specified by the camera
    */
  public Ray ray(int i, int j) {
    Ray ray = new Ray();
    ray.Direction.set(Xmin+((double)i)*Width+Wo2,
		      Ymax-((double)j)*Height-Ho2,-Zcop); 
    ray.Origin.set(0.0,0.0,Zcop);
    return ray;
  }
}