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Updated documentation for the new 3D clouds code, describing the new XML format, and some hints for editing clouds.

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stuart 2009-10-03 20:34:56 +00:00
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Docs/README.3DClouds
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@ -3,99 +3,35 @@ Configuring 3D Clouds
3D clouds are configured using the file data/cloudlayers.xml.
This file has 3 distinct sections: layers, cloud boxes and clouds.
This file has 3 distinct sections: layers, cloud boxes and clouds,
described below.
Note that all distances are in m.
Layers
======
The <layers> section contains definitions for a specific layer type.
The layer type is derived from the METAR/Weather settings by FG itself.
Each layer type is a named XML tag, i.e.: ns, sc, st, ac, sb, cu.
If a layer type is not defined, then a 2D layer is used instead.
The layer type contains one or more <cloud> definitions. This
defines a type of cloud box, and a weighting for that type (<count>).
For example, the following XML fragment will produce 3 "cb" cloud boxes
for every 1 "cu":
<cloud>
<name>cb</name>
<count>3</count>
</cloud>
<cloud>
<name>cu</name>
<count>1</count>
</cloud>
The layer type contains <grid-x-size> and <grid-y-size> tags. These
define the distribution of clouds within the layer in meters, assuming
100% cloud cover (i.e. 8 octas, or "overcast). If the cloud coverage is
less than over-cast, then a proportional number of clouds will be displayed.
<grid-x-rand>, <grid-y-rand>, <grid-z-rand> add a random element to the
cloud grid.
For example, the following XML fragment will produce a grid of clouds
every 4500m +/- 500m, varying in height by 150m.
<grid-x-size type="double">4500.0</grid-x-size>
<grid-y-size type="double">4500.0</grid-y-size>
<grid-x-rand type="double">500.0</grid-x-rand>
<grid-y-rand type="double">500.0</grid-y-rand>
<grid-z-rand type="double">150.0</grid-z-rand>
If the cloud coverage is less than 100%, then a proportion of grid
points are not used.
Cloud Boxes
===========
The <boxes> section contains definitions of cloud boxes. A cloud box
defines a structured group of clouds. For example and entire towering
CB.
The <boxes> section contains a number of named types, as referenced
by the <cloud> section of <layers>. Therefore, the names used are
completely user-defined.
Each type consists of one or more clouds, with an x,y,z position
relative to each other.
For example, the following cloud box defines "sc" as a box containing
two "ns-large" clouds, one at the defined grid position, and one offset
by 500m horizontally:
<sc>
<box>
<x>0</x>
<y>0</y>
<z>0</z>
<type>ns-large</type>
</box>
<box>
<x>500</x>
<y>0</y>
<z>0</z>
<type>ns-large</type>
</box>
</sc>
If the /sim/rendering/clouds3d-density is less than 1.0 (100%), then a
proportional number of clouds will be displayed.
Notes for those editing clouds:
- All distances are in m. Note that this is in contrast to cloud heights
in METAR etc. which are in ft.
- The XML file is loaded into the properties system, so you can modify
the settings in-sim, and see the results by re-generating the cloud
layer. The simplest way to do this is to disable METAR, and control
the cloud layers using the Clouds dialog, and in particular the coverage.
- Texture files are in .png format, and have a transparent background.
To make the textures easier to edit, create a black layer behind them,
so there is some contrast between the background and the white cloud.
Having a grid based on the texture dimensions also helps, so you don't
bleed over the edges, which causes ugly sharp horizontal and vertical
lines.
Clouds
======
The <clouds> section contains definitions of clouds themselves, as referenced
by the <type> tag in the <boxes> section. Therefore, the names used are
completely user-defined.
The <clouds> section contains definitions of clouds themselves, built
up of a number of "sprites" - simple 2D textures that are always
rotated to be facing the viewer. These sprites are handled by a OpenGL
Shader - a small program that is run on your graphics card.
Each cloud definition consists of the following tags:
Sets of these clouds are be built up into bigger masses, described below.
Each cloud group has a completely user-defined name, and contains the
following tags.
<min-cloud-width-m> - minimum width of the cloud
<max-cloud-width-m> - maximum width of the cloud
@ -113,5 +49,89 @@ Each cloud definition consists of the following tags:
<min-sprite-height-m> - minimum height of the spites used to create the cloud
<max-sprite-height-m> - maximum height of the sprites used to create the cloud
The cloud is generated from a number of sprites, placed on the surface of a squashed sphere. Sprites at the bottom of the sphere can be darker than those
at the top, to simulate the darker bases of CBs, for example.
The texture to use for the sprites is defined in the XML <texture> tag.
To allow some variation, you can create a texture file containing multiple
sprites in a grid, and define the <num-textures-x/y> tags. The code
decides which texture to use for a given sprite : randomly in the x-direction
and based on the altitude of the sprite within the cloud in the y-direction.
Therefore, you should put sprite textures you want to use for the bottom of
your cloud at the bottom of the texture file, and those you want to use for
the top of the cloud at the top of the texture file.
Cloud Boxes
===========
The <boxes> section contains definitions of groups of cloads,for example
an entire towering CB mass.
The <boxes> section contains a number of named types, which are referenced
by the <layers> section, described below. Therefore, the names used are
completely user-defined.
Each of the named section consists of one or more <box> section,
defining a particular cloud type
Each <box> section contains the following tags:
<type> - The cloud to use, defined above
<count> - The number of clouds to generate (+/- 50%)
<width> - The x and y within which these clouds should be generated
<height> - The height within which the clouds should be generated
<hdist> - The horizontal distribution of the clouds within the area.
Equates to a sum of random distributions. Defaults to 1.
1 = even distribution, 2 = distributed towards the center.
3 = very strongly distributed towards the center.
<vdist> - The vertical distribution of the clouds. As for hdist.
If the /sim/rendering/clouds3d-density is less than 1.0 (100%), then a
proportional number of clouds will be displayed.
The following example shows a stratus cloud group, which consists of 5
st-large clouds and 5 st-small clouds, distributed in a box 2000mx2000m,
and 100m high, evenly distributed.
<st>
<box>
<type>st-large</type>
<count>5</count>
<width>2000</width>
<height>100</height>
</box>
<box>
<type>st-small</type>
<count>5</count>
<width>2000</width>
<height>100</height>
</box>
</st>
Layers
======
The <layers> section contains definitions for a specific layer type.
The layer type is derived from the METAR/Weather settings by FG itself.
Each layer type is a named XML tag, i.e.: ns, sc, st, ac, cb, cu.
If a layer type is not defined, then a 2D layer is used instead.
The layer type contains one or more <cloud> definitions. This
defines a type of cloud box, and a weighting for that type (<count>).
For example, the following XML fragment will produce 3 "cb" cloud boxes
for every 1 "cu":
<cloud>
<name>cb</name>
<count>3</count>
</cloud>
<cloud>
<name>cu</name>
<count>1</count>
</cloud>
Clouds are randomly distributed across the sky in the x/y plane, but the
height of them is set by the weather conditions, with a random height range
applied, defined by <grid-z-rand>