Add drag and drop support for images and assets (#1497)

scripts/drag_drop_handler.lua

@@ -0,0 +1,43 @@
+-- This script gets two parameters in its global scope:
+-- filename:   The full path for the file that was dropped on the application.
+--             Example:  C:/OpenSpace/openspace.cfg
+-- basename:   Only the name of the actual file with extension, but without the full rest
+--             of the path.
+--             Example:  openspace.cfg
+-- extension:  The extention of the file
+--             Example: .cfg
+--
+-- From this script, we need to return the script that we want to be executed in response
+-- to the drag event.  If we don't want anything to happen, don't return anything or
+-- return an empty string
+
+if filename == nil or filename == "" or
+   basename == nil or basename == "" or
+   extension == nil or extension == "" then
+  do return "" end
+end
+
+-- Lua doesn't enjoy \ that are used by Windows extensively. So we convert all \ into /
+filename = filename:gsub("\\", "/")
+basename = basename:gsub("\\", "/")
+basename_without_extension = basename:sub(0, #basename - extension:len())
+
+is_image_file = function(extension)
+  return extension == ".png" or extension == ".jpg" or extension == ".jpeg" or
+         extension == ".tif" or extension == ".tga" or extension == ".bmp" or
+         extension == ".psd" or extension == ".gif" or extension == ".hdr" or
+         extension == ".pic" or extension == ".pnm"
+end
+
+if is_image_file(extension) then
+  identifier = basename_without_extension:gsub(" ", "_")
+  return [[openspace.addScreenSpaceRenderable({
+    Identifier = "]] .. identifier .. [[",
+    Type = "ScreenSpaceImageLocal",
+    TexturePath = "]] .. filename .. [["
+  });]]
+elseif extension == ".asset" then
+  return [[openspace.asset.add("]] .. filename .. [[")]]
+elseif extension == ".osrec" or extension == ".osrectxt" then
+  return [[openspace.sessionRecording.startPlayback("]] .. basename .. [[")]]
+end