Update README file to cover new 3D cloud commands.
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Stuart Buchanan
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Configuring 3D Clouds
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=====================
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3D clouds are configured using the file data/cloudlayers.xml.
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3D clouds can be created in two ways:
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- By placing individual clouds using a command (e.g. from Nasal)
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- Using the global weather function, which reads cloud definition from
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an XML file.
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This file has 3 distinct sections: layers, cloud boxes and clouds,
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Placing Clouds Individually
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===========================
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Clouds are created using the "add-cloud" command, passing a property
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node defining the location and characterstics of the cloud.
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Location is defined by the following properties:
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<layer> - The cloud layer number to add the cloud to. (default 0)
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<index> - A unique identifier for the cloud in the layer. If a cloud
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already exists with this index, the new cloud will not be
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created, and 0 is returned.
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<lon-deg> - Longitude to place the cloud, in degrees (default 0)
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<lat-deg> - Latitude t place the cloud, in degrees (default 0)
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<alt-ft> - Altitude to place the cloud, relative to the layer (!) in ft
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(default 0)
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<x-offset-m> - Offset in m from the lon-deg. +ve is south (default 0)
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<y-offset-m> - Offset in m from the lat-deg. +ve is east (default 0)
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The cloud itself is built up of a number of "sprites" - simple 2D textures
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that are always rotated to be facing the viewer. These sprites are handled
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by a OpenGL Shader - a small program that is run on your graphics card.
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The cloud is defined by the following properties:
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<min-cloud-width-m> - minimum width of the cloud in meters (default 500)
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<max-cloud-width-m> - maximum width of the cloud (default min-cloud-width-m)
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<min-cloud-height-m> - minimum height of the cloud (default min-cloud-width-m)
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<max-cloud-height-m> - maximum height of the cloud (default max-cloud-width-m)
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<texture> - texture file of sprites to use (default cl_cumulus.png)
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<num-textures-x> - number of cloud textures defined horizontally in the
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texture file (default 4)
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<num-textures-y> - number of cloud textures defined vertically in the
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texture file (default 4)
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<num-sprites> - Number of sprite to generate for the cloud (default 20)
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<bottom-shade> - Light multiplier for sprites at the bottom of the cloud
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(default 1.0)
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<min-sprite-width-m> - minimum width of the sprites used to create the cloud
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(default 200)
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<max-sprite-width-m> - maximum width of the sprites used to create the cloud
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(default min-sprite-width-m)
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<min-sprite-height-m> - minimum height of the spites used to create the cloud
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(default min-sprite-width-m)
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<max-sprite-height-m> - maximum height of the sprites used to create the cloud
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(default max-sprite-height-m)
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The texture to use for the sprites is defined in the <texture> tag.
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To allow some variation, you can create a texture file containing multiple
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sprites in a grid, and define the <num-textures-x/y> tags. The code
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decides which texture to use for a given sprite : randomly in the x-direction
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and based on the altitude of the sprite within the cloud in the y-direction.
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Therefore, you should put sprite textures you want to use for the bottom of
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your cloud at the bottom of the texture file, and those you want to use for
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the top of the cloud at the top of the texture file.
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For example, the following Nasal snippet will create a cloud immediately above the
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aircraft at an altitude of 1000 ft above /environment/clouds/layer[0]/elevation-ft :
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var p = props.Node.new({ "layer" : 0,
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"index": 1,
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"lat-deg": getprop("/position/latitude-deg"),
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"lon-deg": getprop("/position/longitude-deg"),
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"alt-ft" : 1000 });
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fgcommand("add-cloud", p);
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Moving Individual Clouds
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========================
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Clouds may be moved by using the "move-cloud" command. This takes the following
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property arguments.
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<layer> - The cloud layer number containing the cloud to move. (default 0)
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<index> - The unique identifier of the cloud to move.
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<lon-deg> - Longitude to place the cloud, in degrees (default 0)
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<lat-deg> - Latitude t place the cloud, in degrees (default 0)
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<alt-ft> - Altitude to place the cloud, relative to the layer (!) in ft
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(default 0)
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TODO: Add offset arguments for consistency with add-cloud.
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Deleting Individual Clouds
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===========================
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Clouds may be deleted by using the "del-cloud" command. This takes the following
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property arguments.
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<layer> - The cloud layer number containing the cloud to delet. (default 0)
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<index> - The unique identifier of the cloud to delete.
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Global 3D Clouds
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================
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The global weather system uses sets of clouds defined in cloudlayers.xml
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in your FG_ROOT.
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The file has 3 distinct sections: layers, cloud boxes and clouds,
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described below.
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Notes for those editing clouds:
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@ -23,41 +121,9 @@ Notes for those editing clouds:
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Clouds
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======
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The <clouds> section contains definitions of clouds themselves, built
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up of a number of "sprites" - simple 2D textures that are always
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rotated to be facing the viewer. These sprites are handled by a OpenGL
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Shader - a small program that is run on your graphics card.
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Sets of these clouds are be built up into bigger masses, described below.
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Each cloud group has a completely user-defined name, and contains the
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following tags.
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<min-cloud-width-m> - minimum width of the cloud
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<max-cloud-width-m> - maximum width of the cloud
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<min-cloud-height-m> - minimum height of the cloud
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<max-cloud-height-m> - maximum height of the cloud
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<texture> - texture file of sprites to use
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<num-textures-x> - number of cloud textures defined horizontally in the
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texture file
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<num-textures-y> - number of cloud textures defined vertically in the
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texture file
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<num-sprites> - Number of sprite to generate for the cloud
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<bottom-shade> - Light multiplier for sprites at the bottom of the cloud.
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<min-sprite-width-m> - minimum width of the sprites used to create the cloud
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<max-sprite-width-m> - maximum width of the sprites used to create the cloud
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<min-sprite-height-m> - minimum height of the spites used to create the cloud
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<max-sprite-height-m> - maximum height of the sprites used to create the cloud
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The texture to use for the sprites is defined in the XML <texture> tag.
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To allow some variation, you can create a texture file containing multiple
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sprites in a grid, and define the <num-textures-x/y> tags. The code
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decides which texture to use for a given sprite : randomly in the x-direction
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and based on the altitude of the sprite within the cloud in the y-direction.
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Therefore, you should put sprite textures you want to use for the bottom of
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your cloud at the bottom of the texture file, and those you want to use for
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the top of the cloud at the top of the texture file.
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The cloud definitions are as described above for placing individual
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clouds, but no position information is used (this is defined in the
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cloud box and layers below).
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Cloud Boxes
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===========
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