Adding Backgrounds
Motivation
- Shapes form the foreground of your scene
- You can add a background to provide context
Backgrounds describe:
- Sky and ground colors
- Panorama images of mountains, cities, etc
Backgrounds are faster to draw than if you used shapes to build them.
Using the background components
A background creates three special shapes:
- A sky sphere
- A ground hemisphere inside the sky sphere
- A panorama box inside the ground hemisphere
How does the background look like:
- The sky sphere and ground hemisphere are shaded with a color gradient.
- The panorama box is texture mapped with six images.
- Transparent parts of the ground hemisphere reveal the sky sphere
- Transparent parts of the panorama box reveal the ground and sky
- The viewer can look up, down, and side-to-side to see different parts of the background
- The viewer can never get closer to the background
Syntax: Background
A Background node describes background colors;
- skyColor and skyAngle - sky gradation
- groundColor and groundAngle - ground gradation
XML Encoding
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<Background
skyColor='0.1 0.1 0.0, ...'
skyAngle='1.309, 1.571, ...'
groundColor='0.0 0.2 0.7, ...'
groundAngle='1.309, 1.571, ...'/>
Classic VRML Encoding
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Background {
skyColor [ 0.1 0.1 0.0, ... ]
skyAngle [ 1.309, 1.571, ... ]
groundColor [ 0.0 0.2 0.7, ... ]
groundAngle [ 1.309, 1.571, ... ]
}
Using sky angles and colors
- The first sky color is at the north pole
- The remaining sky colors are at given sky angles
- The maximum angle is 180 degrees = 3.1415 radians (π)
- The last color smears on down to the south pole
Using ground angles and colors
- The first ground color is at the south pole
- The remaining ground colors are at given ground angles
- The maximum angle is 90 degrees = 1.5708 radians (π/2)
- After the last color, the rest of the hemisphere is transparent
A sample background
XML Encoding
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<Background DEF='Summer'
skyAngle='0.8,
1.3,
1.4,
1.5708'
skyColor='0.21 0.31 0.59,
0.33 0.45 0.7,
0.57 0.66 0.85,
0.6 0.73 0.89,
0.7 0.83 0.98'
groundAngle='0.659972,
1.2,
1.39912,
1.5708'
groundColor='0.105712 0.156051 0.297,
0.187629 0.255857 0.398,
0.33604 0.405546 0.542,
0.3612 0.469145 0.602,
0.39471 0.522059 0.669'/>
Classic VRML Encoding
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DEF Summer Background {
skyAngle [
0.8,
1.3,
1.4,
1.5708
]
skyColor [
0.21 0.31 0.59,
0.33 0.45 0.7,
0.57 0.66 0.85,
0.6 0.73 0.89,
0.7 0.83 0.98
]
groundAngle [
0.659972,
1.2,
1.39912,
1.5708
]
groundColor [
0.105712 0.156051 0.297,
0.187629 0.255857 0.398,
0.33604 0.405546 0.542,
0.3612 0.469145 0.602,
0.39471 0.522059 0.669
]
}
Example
Syntax: Background
A Background node describes background images:
- frontUrl, etc - texture image URLs for box
XML Encoding
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<Background
...
frontUrl='"cloud1s.png"'
backUrl='"cloud2s.png"'
leftUrl='"cloud3s.png"'
rightUrl='"cloud4s.png"'
topUrl='"sun.png"'
bottomUrl='"ground.png"'/>
Classic VRML Encoding
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Background {
...
frontUrl "cloud1s.png"
backUrl "cloud2s.png"
leftUrl "cloud3s.png"
rightUrl "cloud4s.png"
topUrl "sun.png"
bottomUrl "ground.png"
}
A sample background image
 |  |
| Color portion of clouds texture | Transparency portion of clouds texture |
A sample background
XML Encoding
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<!-- no top or bottom images -->
<Background DEF='Summer'
frontUrl='"clouds1.png"'
backUrl='"clouds2.png"'
leftUrl='"clouds3.png"'
rightUrl='"clouds4.png"'
skyAngle='0.8,
1.3,
1.4,
1.5708'
skyColor='0.21 0.31 0.59,
0.33 0.45 0.7,
0.57 0.66 0.85,
0.6 0.73 0.89,
0.7 0.83 0.98'
groundAngle='0.659972,
1.2,
1.39912,
1.5708'
groundColor='0.105712 0.156051 0.297,
0.187629 0.255857 0.398,
0.33604 0.405546 0.542,
0.3612 0.469145 0.602,
0.39471 0.522059 0.669'/>
Classic VRML Encoding
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DEF Summer Background {
frontUrl "clouds1.png"
backUrl "clouds2.png"
leftUrl "clouds3.png"
rightUrl "clouds4.png"
skyAngle [
0.8,
1.3,
1.4,
1.5708
]
skyColor [
0.21 0.31 0.59,
0.33 0.45 0.7,
0.57 0.66 0.85,
0.6 0.73 0.89,
0.7 0.83 0.98
]
groundAngle [
0.659972,
1.2,
1.39912,
1.5708
]
groundColor [
0.105712 0.156051 0.297,
0.187629 0.255857 0.398,
0.33604 0.405546 0.542,
0.3612 0.469145 0.602,
0.39471 0.522059 0.669
]
# no top or bottom images
}
Example
Summary
Backgrounds describe:
- Ground and sky color gradients on ground hemisphere and sky sphere
- Panorama images on a panorama box
The viewer can look around, but never get closer to the background.
This post is licensed under CC BY 4.0 by the author.