dick balaska <dic### [at] buckosoftcom> wrote:

> It's not a gun, Mom, it's a flashlight. It just looks like a gun.


> I wondered if doing it in two rotates was an answer, as opposed to
> rotate <x, y, 0>

Yes, because the POV-Ray coordinate system is in x, y, z Cartesian space, not
spherical coordinates.
If you are getting a vector as a result, then you can likely just translate that
to spherical coordinates.


> Well, you should. There is no greater purpose in life than helping a
> fellow anonymous POV-er.  I don't want no excuses about last night.

Slave.
Driver.


Give the following a whirl and see if you follow what's going on:

#################################################################

#version 3.71;

#declare Radiosity = off;

global_settings {
 assumed_gamma 1
 #if (Radiosity)
  radiosity {
   pretrace_start 0.04
   pretrace_end 0.01
   count 200
   recursion_limit 3
   nearest_count 10
   error_bound 0.5
  }
 #end
}

#include "colors.inc"
#include "glass.inc"
#include "textures.inc"
#include "metals.inc"
#include "rand.inc"

#declare Perspective = image_width/image_height;
#declare P = Perspective;

#declare Camera = <0, 0, 0>;
camera {
        perspective
        up <0,1,0>
        right x*Perspective
        location Camera
        look_at <0, 0, 1>
        }



light_source {<1, 1, -50> color rgb <1,1,1>}

//plane {y, 0 texture {pigment {Gray50} normal {granite 0.1}} }


#declare Flashlight = <-0.4, -0.3, 0.7>;

#declare Size = 0.025;
#for (Y, -0.5, 0.5, 0.1)
 #for (X, -0.5*P, 0.5*P, 0.1)
  #declare LookAt = <X, Y, 1>;
  sphere {LookAt Size pigment {rgbt <1, 0, 0, 0.9>}}

  // Imagine a sphere at <0, 0, 1>
  // rotating around the x-axis brings the height of the
  // flashlight impact to the same height as the LookAt point
  // Then, when it is rotated around the y-axis, it maintains this height
  // and is oriented to point at the LookAt point
  // Note that this "vector" direction is not corrected for the distance to the
plane
  // and so it is is a cylindrical curve, it is not the same as the Lookat
point,
  // but one can draw a line from the Flashlight
  // to the LookAt point, which is in the +z view plane

  #declare Xo = LookAt.y - Camera.y;
  #declare Xa = LookAt.z - Camera.z;
  #declare XAngle = degrees(atan2 (Xo, Xa));

  #declare Yo = LookAt.x - Camera.x;
  #declare Ya = LookAt.z - Camera.z;
  #declare YAngle = degrees(atan2 (Yo, Ya));

  #declare Xo2 = LookAt.y - Flashlight.y;
  #declare Xa2 = LookAt.z - Flashlight.z;
  #declare XAngle2 = degrees(atan2 (Xo, Xa));

  #declare Yo2 = LookAt.x - Flashlight.x;
  #declare Ya2 = LookAt.z - Flashlight.z;
  #declare YAngle2 = degrees(atan2 (Yo, Ya));

  sphere {<0, 0, 1> Size/2 pigment {rgbt <0, 1, 0, 0.9>} rotate x*XAngle rotate
y*YAngle}

  sphere {<0, 0, 1> Size/4 pigment {White} rotate x*XAngle2 rotate y*YAngle2}

 #end
#end

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