Fast UV island packing add-on for Blender.
Additional information can be found at: https://blenderartists.org/forum/showthread.php?420127-Addon-UV-packing
Use "Install Add-on from File..." in Blender User Preferences/Add-ons and navigate to the downloaded zip-file. Then turn it on in the add-ons tab.
Newer versions (currently only Blender 2.80) require installation of libraries, by pressing the button in the addon settings.
If the UV islands have a lot of broken self overlapping geometry, the results are undefined. It's best to remove doubles before running packing.
The add-on is located in UV/Image editor Tools tab under Shotpacker.
Island iterations determines how many vertical and horizontal locations are tried for each island in the packing algorithm. For example if this value is 100, then different locations tried for the island is 100 times 100 = 10000.
Rotation is rotation step. 0 is no rotation. 90 preserves texel orientation. For example 20 rotation means the island is rotated to 360/20=18 different positions at every checkpoint. 20 rotation also increases the running time 18x.
Mirror allows or disallows mirroring the island over an axis.
Margin determines how big the edge margin is for the island. 100.0 (%) is the length of the entire UV area. So something like 0.5 is in the reasonable range. For example with 1024x1024 textures, 10 pixels is 10/1024 = ~1.0 (%)
Island selection behavior options
Pack all packs everything not caring about what is selected.
Selected packs only selected but scales everything making it fit into the 0-1 UV area.
Ignore ignores everything that is not selected and simply packs selected treating the unselected as if they didn't exist.
Lock locks the unselected islands not moving them and trying to fit the selected islands into the cracks. If it doesn't find fit, the islands will go over the 0-1 UV area.
Overlap detectionIf turned on, keeps UV islands together when packing.
Keeps trying new solutions. Can be stopped using esc key. Saves the best solution it finds, doesn't change anything if no better solution found. Will automatically end after running a scan and now new better solutions found.
When you're satisfied with parameters, just click Start pack to start the algorithm.
You can optionally turn on Blender console (Main Menu > Window > Toggle System Console) to see what the add-on is doing in a more verbose form.