The background node provides a way to describe the horizon of your world.
This is a bindable node.
The background node allows you to define the sky, ground, and panorama
images to add an horizon to your world. All items on the background are
placed as if infinitely far away from you, i.e., you can never get closer
to the background images.
Syntax:
Background {
skyColor [ 0 0 0 ]
skyAngle [ ]
groundColor [ ]
groundAngle [ ]
backUrl [ ]
bottomUrl [ ]
leftUrl [ ]
rightUrl [ ]
frontUrl [ ]
topUrl [ ]
}
The sky is defined as a infinitely large sphere placed around your world.
You can define a constant color for it, or have gradient effects.
The sky color is defined by two fields: skyColor and skyAngle.
If you want a single color sky, like the figure on the left above, then
you specify a skyColor as the RGB of the desired color, don't specify
the skyAngle. The skyAngle is only used when a gradient effect,
like the image on the right above, is intended. If you want a gradient
effect then you specify the color for the upper pole of the sphere as the
first color in the field skyColor. Next you specify at which angle you
want a new color (the angle is measured from the upper pole) in the skyAngle.
The second color in the skyColor field specifies this last color. The browser
should create a gradient between the first and second colors, starting
at the upper pole and ending at the angle specified in the skyAngle
field. You can specify any number of colors and angles, the number of angles
should be the number of colors less 1. The first color always corresponds
to the upper pole. For instance the following combinations were used to
create the above images:
Left Image
SkyAngle
SkyColor
upper Pole
0 0 1
Right Image
SkyAngle
SkyColor
Upper Pole
0 0 1
1.2
0 0 0.6
1.57
1 0 0
On the left image only one color was specified. In this case no angles
are specified because the first color is always the upper pole color. The
Sky is all blue.
On the right image from 1.57, roughly 90 degrees, to the lower pole the
color used is the last color specified, i.e. red.
Similarly to the sky, the ground is also an infinitely large sphere. The
ground sphere is placed inside the sky sphere. The only difference between
these two spheres is that in the ground sphere if you do not specify a
color, you can see through it, i.e. you can see the sky sphere. Usually,
for the ground sphere colors are only provided for the bottom hemisphere.
The following images provides a ground combined with a sky.
The ground color and angles used were:
groundAngle
groundColor
lower pole
0.5 0.5 0
1.57
0.5 0.5 0
From 1.57 radians to the upper pole the ground is transparent because no
color was specified, therefore allowing you to see the sky sphere. Note
that you must specify at least two colors for the ground, otherwise there
will be no ground. If you want a ground with a constant color just specify
twice the same color. Specifying only one color doesn't provide you with
a background.
You can place images on the sides, top and bottom of a conceptually infinitely
large box placed inside the ground sphere. Since the box is placed
inside the sky and ground spheres, in order to see through these you should
use images with transparent parts.
The image used for the sides of the box is
The border presented in the image is only to give you the notion of the
image size, it is not part of the image. Black is the transparent color
of this image. Looking at the image one can see that the mountains start
only at half of the image, they don't start from the bottom of the image.
This is because the desired effect was to have the mountains starting when
the ground was over and the sky started.