### Modifying the parameters ( Tut04.rt )

Now you may want to change some image characteristics, like the image dimension: in fact a 100 x 100 image may be too small. To do this, you must add a new section.

Look at file tut04.rt . There is a new param section.

Param section allows to change the parameters which determinate the way to build the image. Below are described the principal attribute of param section:

dimx, dimy

represent the image dimension in pixel ( default is 100x100 ).

If you change the image dimension, and horizontal dimension becames different from vertical, you can affect the aspect ratio, so circles became ellipses and squares rectangles. To avoid this you must change the view window in the view section ( look at paragraph "Understanding the view" ), or , simply, always use squared image of any dimension, with dimx = dimy.

shade

is the way the color will be computed. The allowed values are "phong" and "noshadowsphong". The default is "phong". "phong" and "noshadowphong" are similar, but "noshadowphong" does not compute the shadows. It is faster, but the image could be lighter.

mode

is the number of deviation allowed for a ray. If you set =0 you will not see transparency and reflection. Don' t specificate big value. A value of 5 or 7 is good for transparence.

anti_alias

is a technique for creating a smoothed image. Set to 1 if you want, o if not. The program will use adaptive antialiasing.

backcolor

is the color of the background. its value is in rgb format.

buildhier if set to 1, create an automatic hierarchy to speedup the creation of the image. If set to 0 no hierarchy is used. This will be explained later.