   Ray-Tracing with POV-Ray version 1  
                                       
        Hints by Mike Williams.        
                                       
   In the camera section there is a    
field called 'Right' which can be used 
to set the shape of the picture to     
match the shape of the pixels in the   
target computer. The correct value for 
an Archimedes screen is <1.25 0 0>. At 
this setting your spheres will look    
spherical when you render a screen     
shaped image. <1.33333 0 0> is correct 
for Amiga shaped pixels. If you intend 
the image to be correct in unusual     
screen modes, then divide the screen   
width in OSUnits by the height in OS   
Units. E.g. for conventional modes 1280
divided by 1024 = 1.25, mode 40 1792/  
1408 = 1.2727.                         
   Risc OS 3.1 POVRay bugfix - If you  
render two images at the same time,    
when you QUIT from one of the tasks,   
the computer hangs. Fix: Remove the    
final blank line in !POVRay.!RunPOV.   
(Or just press ESCAPE).                
  New features from POVRay Beta version
0.5 - I've noticed the following so far
It's a bit faster. The syntax has      
significantly changed. The image is    
noticably darker, it may be necessary  
to add more lights. Light_Source is a  
new type of object, it is invisible, so
you can now put light sources inside   
the field of view without seeing them. 
It is possible to apply a zoom or wide-
angle lens to the camera by setting the
direction to something like <0 0 1.4>. 
The 'fov' file contains some field-of- 
view values which correspond to focal  
lengths commonly used for lenses. Box  
is a new, convenient way to describe a 
cuboid, eg. a box {<-1 -1 -1> <1 1 1> }
 is a cube. The vectors specify the    
location of two opposite corners.      
   Octaves is a new parameter which    
affects the turbulence of a texture.   
Textures without turbulence, eg granite
are not affected. Octaves do something 
like applying a low-pass spatial filter
to the noise function that is used to  
calculate turbulence. 'Octaves 1'      
causes the turbulence to be limited to 
large smooth sweeps. Higher octaves    
make the turbulence more crinkly. My   
guess is that octaves 1 limits the wave
length of the turbulence to be at least
as high as the distance between the    
stripes (or rings, or whatever).       
5 and more is almost indistinguishable 
from the default.                      
   You can reduce the memory required  
for rendering big images by switching  
display off. Version 0.5 always grabbed
enough memory but version 1 only does  
if display is enabled.                 
   Blob - Blob is a powerful new way to
creat some weird shapes that would be  
extremely difficult to describe with   
conventional equations.                
   BLOB ( THRESHOLD t                  
COMPONENT strength radius <position>   
COMPONENT strength radius <position>   
...                                    
   )                                   
   I think of it like this - take a    
number of points in space, each which  
radiates a spherical 'field'. At the   
point itself, the value of the field is
specified by the 'strength' parameter. 
As you move further from the point, the
field decreases smoothly. At 'radius'  
the value of the field reaches zero.   
The blob consists of all points in     
space where the sum of the field values
is greater than threshold t. When t is 
0 the blob is exactly the same as union
of spheres at those points, with those 
radii. As t increases, the blob shrinks
but if t=strength, then the only points
inside the blob are the component      
points themselves. Between these limits
the blob takes on various amoeboid     
shapes. The ratio of the radius to the 
distance between points seems to need  
to be <0.75 or >1.25, otherwise you get
a rather ugly effect.                  
   On the down side - The quality of   
images displayed directly by POVay is  
even worse than before. It is more     
important than ever before to create a 
Clear, Targa or Dump file and get that 
converted to a sprite by ChangeFSI or  
Translator.                            
   More features I think are new since 
version 0.5 - Default { { ... } } is   
for setting default values of Specular,
Ambient, Diffuse, etc. here and these  
values will be used for all following  
objects unless overridden by local     
texture commands.                      
   Tiles appears to be the new word for
Checker_texture.                       
   Well that's it this issue from the  
master of Ray Tracing - Mike Williams. 
                                       
                                       
                                       
                                       
                                       
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