// Persistence of Vision SDL include file
// Description: A macro to simulate lens movements in architectural scenes
//		Helps prevent the "falling verticals syndrome"
// Author: John Guthkelch (Doctor John) <docjohn@linuxmail.org> 
// Version 3.0 Released May 2006
// History:
//      Version 3.0: 1. Removed necessity of passing parameters when calling
//                      macro. Less typing needed :-)
//                   2. Added code so macro can be used when using right-handed
//                      coordinates (i.e. z-axis is up).
//      Version 2.0: 1. Improved warning so that camera automatically reverts to
//                      default type if insane values are given for CamPos 
//                      and/or CamLook
//                   2. Corrected silly mathematical error in vertical
//                      scaling.This is now correct so switch has been taken out.

/***********************************************************************
License & copyright:
(c) 2006 John Guthkelch
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version. This program is distributed in the hope that
it will be useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
the GNU General Public License for more details.
(See http://www.gnu.org/licenses/gpl.txt for the full GPL text)

***********************************************************************/
#macro FieldCam()
        #local CD=CamLook-CamPos;
        #ifndef (Up_Z)
                #if (CD.x!=0 | CD.z!=0) // Note: That's a Boolean OR not an
                                        // uppercase i or a lowercase L!
                        #local HypoXZ=sqrt(pow(CD.x, 2)+pow(CD.z, 2));
                        #local VCorr=pow(vlength(CD), 2)/pow(HypoXZ, 2);
                        #local CosThetaX=CD.x/HypoXZ;
                        #local CosThetaZ=CD.z/HypoXZ;
                        #if (CD.x=0)
                                #local ShearX=0;
                        #else
                                #local ShearX=(CD.y/CD.x)*pow(CosThetaX, 2);
                        #end
                        #if (CD.z=0)
                                #local ShearZ=0;
                        #else
                                #local ShearZ=(CD.y/CD.z)*pow(CosThetaZ, 2);
                        #end
                        #declare NoFall=transform {
                                matrix <1, 0, 0, ShearX, VCorr, ShearZ, 0, 0, 1, 0, 0, 0>
                        }
                #else
                        #warning "Viewing vector is perpendicular to XZ-plane.\n"
                        #warning "Camera changed to default type.\n"
                        #declare NoFall=transform {
                                matrix <1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0>
                        }
                #end
        #else
                #if (CD.x!=0 | CD.y!=0) // Note: That's a Boolean OR not an
                                        //uppercase i or a lowercase L!
                        #local HypoXY=sqrt(pow(CD.x, 2)+pow(CD.y, 2));
                        #local VCorr=pow(vlength(CD), 2)/pow(HypoXY, 2);
                        #local CosThetaX=CD.x/HypoXY;
                        #local CosThetaY=CD.y/HypoXY;
                        #if (CD.x=0)
                                #local ShearX=0;
                        #else
                                #local ShearX=(CD.z/CD.x)*pow(CosThetaX, 2);
                        #end
                        #if (CD.y=0)
                                #local ShearY=0;
                        #else
                                #local ShearY=(CD.z/CD.y)*pow(CosThetaY, 2);
                        #end
                        #declare NoFall=transform {
                                matrix <1, 0, 0, 0, 1, 0, ShearX, ShearY, VCorr, 0, 0, 0>
                        }
                #else
                        #warning "Viewing vector is perpendicular to XY-plane.\n"
                        #warning "Camera changed to default type.\n"
                        #declare NoFall=transform {
                                matrix <1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0>
                        }
                #end
        #end
#end

/*********************************USAGE 1************************************

#declare CamPos=<Xc, Yc, Zc>;   // Just replace <Xc,Yc,Zc> with location vector
#declare CamLook=<Xl, Yl, Zl>;  // -"-    -"-   <Xl,Yl,Zl> with look_at vector
[#declare Up_Z=1;] // Only use this #declare when using right-handed coordinates

camera {
        FieldCam ()
        perspective
        location CamPos
        [angle Whatever] // Not essential but can be used
        [right If_you_want] // Also not essential but can be used
        up y | up z //whichever you need
        transform {NoFall}
        look_at CamLook
}
**********************************USAGE 2************************************
Don't forget to switch vista buffer off by putting Vista_Buffer=0 in your 
.ini file or using -uv on the command line.
****************************************************************************/