Charles wrote:

> Curious, not to find in the POV documentation, where I looked first. No word
> about bump_map.

Bump mapping is part of the normal feature and is well documented.


Bump Maps

When all else fails and none of the above normal pattern types meets your
needs you can use a bump_map to wrap a 2-D bit-mapped bump pattern around
your 3-D objects.

Instead of placing the color of the image on the shape like an image_map
a bump_map perturbs the surface normal based on the color of the image at
that point. The result looks like the image has been embossed into the
surface. By default, a bump map uses the brightness of the actual color
of the pixel. Colors are converted to gray scale internally before
calculating height. Black is a low spot, white is a high spot. The image's
index values may be used instead (see section "Use_Index and Use_Color"
below).

Specifying a Bump Map

The syntax for an bump_map is:

BUMP_MAP:

normal{
bump_map{ BITMAP_TYPE "bitmap.ext" [BUMP_MAP_MODS...] } 
[NORMAL_MODFIERS...] 
}

BITMAP_TYPE:

gif | tga | iff | ppm | pgm | png | sys

BUMP_MAP_MOD:

map_type Type | once | interpolate Type | 
use_color | use_colour | bump_size Value

After the required BITMAP_TYPE keyword is a string expression containing
the name of a bitmapped bump file of the specified type. Several optional
modifiers may follow the file specification. The modifiers are described
below. Note that earlier versions of POV-Ray allowed some modifiers before
the BITMAP_TYPE but that syntax is being phased out in favor of the syntax
described here. Note sys format is a system-specific format such as BMP for
Windows or Pict for Macintosh.

Filenames specified in the bump_map statements will be searched for in the
home (current) directory first and, if not found, will then be searched for
in directories specified by any +L or Library_Path options active. This
would facilitate keeping all your bump maps files in a separate subdirectory
and giving a Library_Path option to specify where your library of bump maps
are. See "Library Paths" for details.

By default, the bump pattern is mapped onto the x-y-plane. The bump pattern
is projected onto the object as though there were a slide projector somewhere
in the -z-direction. The pattern exactly fills the square area from (x,y)
coordinates (0,0) to (1,1) regardless of the pattern's original size in
pixels. If you would like to change this default you may translate, rotate
or scale the pigment or texture to map it onto the object's surface as
desired. If you would like to change this default orientation you may
translate, rotate or scale the pigment or texture to map it onto the object's
surface as desired.

The file name is optionally followed by one or more BITMAP_MODIFIERS. The
bump_size, use_color and use_index modifiers are specific to bump maps and
are discussed in the following sections. See section "Bitmap Modifiers" for
the generic bitmap modifiers map_type, once and interpolate described in
"Bitmap Modifiers"

Bump_Size

The relative bump size can be scaled using the bump_size modifier. The bump
size number can be any number other than 0 but typical values are from about
0.1 to as high as 4.0 or 5.0.

  normal {
    bump_map {
      gif "stuff.gif"
      bump_size 5.0
    }
  }

Originally bump_size could only be used inside a bump map but it can now be
used with any normal. Typically it is used to override a previously defined
size. For example:

  normal {
    My_Normal   //this is a previously defined normal identifier
    bump_size 2.0
  }

Use_Index and Use_Color

Usually the bump map converts the color of the pixel in the map to a gray
scale intensity value in the range 0.0 to 1.0 and calculates the bumps based
on that value. If you specify use_index, the bump map uses the color's palette
number to compute as the height of the bump at that point. So, color number 0
would be low and color number 255 would be high (if the image has 256 palette
entries). The actual color of the pixels doesn't matter when using the index.
This option is only available on palette based formats. The use_color keyword
may be specified to explicitly note that the color methods should be used
instead. The alternate spelling use_colour is also valid. These modifiers
may only be used inside the bump_map statement.



-- 
Ken Tyler

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