DP Tool Club 19/CD_ASCQ_19_010295.iso/vrac/rtbeginr.zip/RAYTRACE.TXT

Text File | 1994-11-07 | 18KB | 441 lines

                             Raytracing Fundamentals


   By the time we are in kindergarten almost all of us can draw simple shapes
like circles, squares, and lines. We would then be able to possibly combine
these shapes to create things such as stick figures. And perhaps some of us
would continue on and draw more realisticly. Finally a selected few of us
might become true artists, using shading and imitating light. Even the most
gifted artists spend a considerable amount of time concentrating on how light
and shadow effects their artwork. When light and shadow are interpreted well
by an artist, the results of his work can be very realistic. Throughout the
years man has been facinated with art, but the skill of actually being a great
artist was limited to only a few gifted people. The advent of the computer has
changed all of this.

   In the 1960's when computers were invented, the makers of these machines
saw them as number crunchers that could not deal with other media. Even though
this was true, I am sure people realized that there were other possibities, as
Havelock Ellis once said "It is here in mathamatics that the artist has the
full scope of his imagination"

  As time went on computers gained artistic capabilities, at the same time
they kept their mathmatical ones. This lead to raytracing, which is the use of
a computer to imitate the behavior of light. The computer and raytracing
software use the laws of physics and then interprets them into mathmatical
equations to best resemble the path that light takes. Doing this takes a
considerable amount of time because the computer makes thousands upon
thousands of floating point calculations, and on even today's fastest
computers a complex scene with many light sources may take a good while. But
this does not limit us, because we still can create the same effects on a
personal computer, it may take a while longer but the results are definitly
worth the wait.

   Raytraced scenes are noted for their extremely realistic apearance and are
often mistaked for photographs. Almost anything is possible with raytracing,
from creating a perfect model of something as simple as a cola bottle, to
something as complicated as a preview of the inside of a building. Animation
is also possible with raytracing, and is used today alot in commercials and
movies.

   With all these possibilities and power of raytracing one might excpect
raytracing software to be too expensive for the average joe, but the truth is
your excpectation is totally wrong. With an IBM PC or compatible you can
create profesional Raytraced images with extremely sofisticated software that
is absolutly FREE!  The reason is that people in the PC world finally got fed
up with the high prices of software, and started a marketing technique that
has revolutionized home computing. It is a concept where the author of some
type of software decides to distribute his software as free. This concept is
called "ShareWare", and it will make your life a whole lot easier if you are
a IBM and compatible PC user. The lack of many shareware programs for the
Macintosh makes it very hard to find in the mac format, but you might find
something, just keep your eyes open.


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   You know what a Raytracer does and how much the cost is, but where do you
get this software? Well there are a few ways, for one you might be able to
download them from a online service such as America Online, and you will
definitly be able to find them on the internet. But if you do not have access
to either you can call a BBS that has these programs. Look in file areas
marked as GRAPHIC UTILITYS or maybe even RAYTRACING. Here is a small list of
some of the raytracers avaliable:

PovRay................The best and most popular Shareware Raytracer avaliable
PolyRay
Vivid
DKB-Trace

   I run a Bulletin Board myself and you may call and download some of these
raytracers along with other thing, my BBS is called FREELOAD BBS, and the
number is [phone]. Look in my GRAPHICS UTILITYS file area.

   Now that you know what raytracers do, and where to get them we can now move
on and see how these wonderfull programs actually work.



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                      Creating a Raytraced Scene With PovRay



   I will be using PovRay in my examples, for it is the most popular and
widely used Raytracer. Now we come to using the raytracer. We will be writing
code to create scenes that will then be compiled by the PovRay into a TGA
image file. One of the most important things you must understand about
Raytracing is the 3-D coordinate System. Its Syntax is <X Y Z>. The X axis
moves Horizontily Left and right, the Y axis moves verticly up and down, and
the Z acces moves forward to backward 3 demensionaly.

   Every RayTraced scene has an origin, which is usually at <0 0 0>, meaning
0 units to the left or right, 0 units up or down, and 0 units forward or
backward.  So a location of <2 3 1> would mean 2 units to the right of the
origin, 3 units above the origin and 1 unit in front of the origin. And
<-2 -3 -1> would mean 2 units to the left of the origin, 3 units below,
and 1 unit in behind it.

   Ok we have a way to measure our scenes, and a way to find locations. Now
we need an Object to be in our scene. The basic geometric shapes (such as the
sphere, box, cone, disk, and triangle) and a few not-so-basic shapes (like
the torus or donut, polynomial, height field, Bezier patch, and triangular
patch) are called primitives. These shapes can be used as buliding blocks
for other more complicated shapes.

   Another thing we need in our scene is a view point, or a "Camera". A camera
is treated as a special object that both has a location and a place to look at
or be pointed at, but can NEVER be seen, because it will be taking the
picture. The following example declares a camera in your scene:

camera {
  location <0 1 -2>
  look_at <0 1 2>
}

This will produce a camera that is located 1 unit above the origin and 2 units
behind it. It would be looking at a location 1 unit above the origin and 2
units in front of the origin.

   All this is great, but there is one thing missing, light. Without light you
cannot see anything,  so now we introduce what is known as the light source.
The light source is treated as an object, meaning you give it a location.
Look at the following example of stating a light source:

object {
  light_source { <3 3 -3> color white }
}

This would creat a light source that produces White Light, 3 units to the
right of the origin, 3 units above the origin, and 3 units in front of the
origin of our scene.

  Next we will actually be creating scenes. You will need a standard ascii
based text editor if you want to actually follow along and create the scenes,
EDIT is an editor that comes with dos, and will work fine. Otherwise if you
don't want to participate you may just simply continue reading.


  With all this knowledge we can finally create something!  This first scene
will be a simple scene with a sphere sitting on an endless plane. The
following is the actual text file with all the code:
NOTE: two /'s represent a comment in a scene so whenever you see //, it means
that is just a comment.

-----------------------------------------------------------------------------
// A shiny red ball on a green floor
camera {
  location <0 1 -2>
  look_at <0 1 2>
}
object {
  sphere { <0 1 2> 1 }
  texture { color red 1 phong 1}
}
object {
  plane { <0 1 0> 0 }
  texture { color green 1 }
}
object {
  light_source { <3 3 -3> color red 1 green 1 blue 1 }
}
------------------------------------------------------------------------------

Now we will tear this apart piece by piece and explain everything. I will
start with the camera.

camera {
  location <0 1 -2>
  look_at <0 1 2>
}

This statement represents a camera that is located 1 unit above and 2 units
behind the sphere. The camera is looking at the location <0 1 2> which is
the location of the sphere

object {
  sphere { <0 1 2> 1 }
  texture { color red 1 phong 1}
}

This statement declares the sphere. This sphere is 1 unit above the origin and
2 units in front of it. The texture statement declares the color, and in this
case Phong which is the size of the highlight on the sphere. So in this scene
the sphere is 100 percent red (red 1) and has a phong size of 1 (phong 1).

}
object {
  plane { <0 1 0> 0 }
  texture { color green 1 }
}

This code declares the plane that the sphere is sitting on. Which you can
simply think of as the floor. As you can see it is green with no phong.



object {
  light_source { <3 3 -3> color red 1 green 1 blue 1 }
}

And the final touch of the scene is the light source, remember without it all
would be useless because we would not be able to see anything in the dark. It
is located 3 units to the right 3 units above and 3 units behind the origin.
The mixture of red green and blue make white, the natural color of light.


   We are now done with creating a small and simple universe. This is one of
the simplist scenes posible, so do not even begin to think this is anywhere
close to the limit, when really the possibilities are absolutly endless!  We
will now move on to slightly more complicated scenes ivolving different shapes
and combining these shapes to create more interesting shapes.


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                   How to make Povray render or compile your scenes

   We know how to describe a scene for Povray, but how do we turn all those
statements into a picture? Well we need to render them. If you have ever done
any programing, you may think of rendering as compiling. If you have not
already, please save the text file you created with your text editor, the
name may be anything with the .POV extension. Now the following command line
will render a scene:

POVRAY +Imyfile +W640 +H480 +Omyfile.tga

First we typed in POVRAY, which is the execution file. Then we added the
switch +I  which is the Input file or your text file, it is immediatly
proceeded by the name of the text file which includes the povray decription
text file. Then we used the +W switch which determines the number of pixels
wide the scene file should be, and the +H switch determines the number of
pixels high the scene should be. Note that you should stick with these basic
sizes:

320 by 200, 320 by 240, 320 by 400, 320 by 480, 360 by 480, 640 by 480,
640 by 400, 800 by 600, 1024 by 768, or 1280 by 1024.

If you use other dimensions you might get a distorted picture. Also note that
the higher the set of numbers the finer the picture quality will be.

Finally we come to the +O switch, this is the filename you want your picture
to be called. The format must be .TGA. But you can change this format with
many different shareware programs, one that I can think of off the top of my
head is GRAPHIC WORK SHOP, and you can find it on my bulletin board.
[phone]



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                           Combining Shapes


   As you may have suspected, we could have possibly included another sphere
into our first scene and had two spheres. Now imagine that we had one sphere
at <0 2 2> and another at <1 2 2>. What do you think would happen? Would they
overlap or would povray give an error message? Well the answer is they would
overlap, Povray will never butt in because of the way you place your objects.
We could possibly use three or four spheres to create something like a snow
man. We might do it by placing spheres closely on top of each other, and
changing the sizes of each sphere. The size of the sphere is defined in its
declaration:

object {
  sphere { <0 2 2> 1 }
}

   The 1 in { <0 2 2> 1 } is the size of the sphere, in this scene the sphere
is 1 unit large, you may size it up or down by changing the number to be
larger, or smaller. For example: { <0 2 2> .4 } would make the sphere smaller
because I used a decimal less then 1, whereas { < 0 2 2> 1.5 } would make the
number larger, because it is greater than 1.

   We have covered the sphere, now we will talk about the box. The syntax for
the box is:

box { <corner1> <corner2> }

   Corner1 is the x,y,z location of one of the box's corners while corner2 is
the x,y,z location of the other corners location. Each of the x,y,z values of
corner1 must be smaller than the coresponding x,y,z location for corner2. The
following is an example of box:

object {
  box { <-1 0 -1> <1 2 1> }
  texture { color red 1 phong 1 }
}

  This box's bottom left back corner is located 1 unit left, and 1 unit behind
the origin, while the oposite corner (The top right front corner) is located
1 unit to the right, 2 units above and 1 unit infront of the origin. This
makes the box 2 units wide, 2 units high, and 2 units long, a perfect cube.
Finally the color of the square is solid red with a phong size of 1. Note that
on a box the phong is not as brilliant as on a sphere, the fact is spheres are
nice and rounded, while box's are flat edged, this causes less highlight.



   Now that we know how to use a box, and that a scene can have multiple
objects to create interesting shapes, we will put this knowledge to work in a
scene that will house a table. The following is the actual code to create this
table scene, we will then pick this code apart and explain it piece by piece.

-----------------------------------------------------------------------------
// A union of several boxes combined to make a table
camera {
  location <5 6 -8>
  look_at <0 5 0>
}
// The union of boxes making the table
object {
  union{
     box { <-2 0 1.5> <-1.5 4 2> }     // Back left leg
     box { <-2 0 -2> <-1.5 4 -1.5> }    // Front left leg
     box { <1.5 0 1.5> <2 4 2> }       // Back right leg
     box { <1.5 0 -2> <2 4 -1.5> }     // Front right leg
     box { <-2.5 4 -2.5> <2.5 4.2 2.5> }  // Table Top
  }
  texture {
     color red 1
   }
}
// A white light source behind and to the right of the camera
object {
  light_source { <10 15 -20> color red 1 green 1 blue 1 }
}
----------------------------------------------------------------------------

Before we pick this code apart I want to explain the union. This scene could
have been made using boxes and squares individualy. For example we could
actually type the following in for EACH of the boxes:

object {
  box { <-2 0 1.5> <-1.5 4 2> }     // Back left leg
  texture { color red 1 }
}

This is how we would think to do it. But there is a better way, why not just
combine all the boxes into one mass and then color the whole mass, this is
what the statement "union" is used for. The syntax for union is:

object {
  union {
     shape_1
     shape_2
     shape_3 ...
   }
}

Union saves alot of key strokes, and gives the advantage of having just one
shape to work with. Now onto explaing the table scene!



camera {
  location <5 6 -8>
  look_at <0 5 0>
}

This as you know is the location and viewpoint of the camera. Pretty much
self explanitory.

object {
  union{
     box { <-2 0 1.5> <-1.5 4 2> }     // Back left leg
     box { <-2 0 -2> <-1.5 4 -1.5> }    // Front left leg
     box { <1.5 0 1.5> <2 4 2> }       // Back right leg
     box { <1.5 0 -2> <2 4 -1.5> }     // Front right leg
     box { <-2.5 4 -2.5> <2.5 4.2 2.5> }  // Table Top
  }
texture {
     color red 1
   }
}

This is the union of boxes that form the table, I am not going to go into how
each box is located because it would take far to long, but it can be simply
figured out. Also note that I did not just make this table straight from my
head, it would be virtualy impossible. Instead I got some graph paper and used
every two squares as a unit, and figured out the locations needed to make a
table, this is the recommended aproach.  Now notice the TEXTURE statement,
using it for the whole union as red 1, makes the whole table red.

object {
  light_source { <10 15 -20> color red 1 green 1 blue 1 }
}

And this is simply the location of the light source that gives off white
light.

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 We have covered alot, but there is still MUCH more to be covered! We cannot
take the time to do it here. But if you are interested in learning more there
are many ways to go about it. For one a good book will teach you alot, here
are a couple I recomend:

* RayTracing Creations by the Waite Group - Excelent book that will teach you
almost everything you need to know about raytracing, this one is highly
recomended.

*  Making Movies on Your PC - This book goes beyond Raytracing still images,
into the world of Raytracing animations.

  If you want to keep up to date and stay in touch with all the Raytracing
attics, you should go online! Here are a few places to try:

* Compuserve Information Service - Goto the GRAPHDEV forum

* You Can Call Me Ray BBS, or YCCMR [phone]  Located in Palatine,
IL. A great bulletin board for graphic freeks.

* The Graphics Alternative BBS or TGA [phone] Located in El Cerito, CA.
A good graphics BBS, with about everything you ever wanted on the subject

* FreeLoad BBS, [phone] Located in San Mateo CA, I run this board. Look
in the Graphics Utilitys File area.

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Ways to reach me electronicly if you have any comments are:

- Through my BBS, FreeLoad BBS [phone] (Leave a comment to the Sysop,
me)

- Through fidonet at 1:125/225

- Through the internet at   [e-mail]



I hope you enjoyed this Text!  And Have Fun!

-John McGraw