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Mission Editing Basics
 
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 Mission Files Adding Missions Conditions & Goals Goals Strings Imports Backdrops
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Thanks to Marcos Edson for the backdrop thumbnail grid used in AlliED, discovering the shadow setting, and the Backdrops 27 and 55 table below.
Backdrops

Backdrops are now significantly more important than in previous games in the series. As well as being a visual element of the "spacescape", they also provide the lighting for the Regions. You have control over the size of the backdrop, as well as the color and intensity of the light it produces, allowing you to create some dramatic lighting effects. Without a backdrop the mission will be very dark, so you should have at least one Backdrop in each Region that you use in a mission.

When you select a Backdrop as the current FG, the Cargo section of the Datapad will change to reflect the backdrop parameters:

Cargo section for Backdrops

The purpose of the FG Name also changes:
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Name For most backdrops, its Name represents the Red / Green / Blue color values of the light it will produce, as a series of 3 numbers. 

1.0 represents the full value for each RGB component i.e. 1.0 1.0 1.0 = white, 1.0 0.0 0.0 = red. However some of the original missions use numbers higher than 1.0; around 1.2, 1.3. From the little testing I've done, these seem to have the effect of making the colored lighting come from the sides, with white light directly in front.
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Brightness This will set the intensity of the light from the backdrop.
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Size Set the size the backdrop will be displayed at, and hence how close you seem to be to it. The bigger you make a backdrop, the more it will "wrap around" the sphere of space.
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A useful technique for backdrops is to have 2 or more in a Region, fairly equally placed around the sphere of space, with one having white light (1.0 1.0 1.0) and the others having different colors coming from different directions. The "star" backdrops are useful for the white light as they are the ones that produce the lens flare.
 


 
  Backdrop selection window

Backdrop window

To bring up the Backdrop window, click on the little planet image that appears next to the backdrop selection box.  To choose a Backdrop, simply click on its thumbnail. Down the right hand side are 7 buttons to choose the size of the shadow which falls across planet-type backdrops. 

Below the shadow settings is a panel which displays the color of the current backdrop. 

Click on the panel to bring up a standard color selection dialogue for setting the color.

 
Backdrops 27 and 55

Besides space objects, these two backdrops also display the several Star Destroyers backdrops seen on the Battle of Endor missions. The backdrop to be displayed is set by the Shadow option.
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Shadow
Backdrop 27
Backdrop 55
None (?)