Add documentation on inspector plugins.

tutorials/plugins/editor/index.rst

@@ -9,3 +9,4 @@ Editor plugins
    making_main_screen_plugins
    import_plugins
    spatial_gizmos
+   inspector_plugins

tutorials/plugins/editor/inspector_plugins.rst

@@ -0,0 +1,83 @@
+.. _doc_inspector_plugins:
+
+Inspector Plugins
+=====================
+
+Introduction
+------------
+
+Godot 3.1 comes with a new inspector. Adding plugins to it is now possible.
+
+This tutorial will explain the process.
+
+
+Inspector Plugin
+----------------
+
+This short tutorial will explain how to make a simple value editor.
+Create an EditorInspectorPlugin first. This is needed to initialize your plugin.
+
+
+.. tabs::
+ .. code-tab:: gdscript GDScript
+    
+    # MyEditorPlugin.gd 
+    
+    extends EditorInspectorPlugin
+    
+    func can_handle(object):
+        # if only editing a specific type
+        # return object is TheTypeIWant
+        # if everything is supported
+        return true
+
+    func parse_property(object,type,path,hint,hint_text,usage):
+        if (type==TYPE_INT):
+             add_custom_property_editor(path,MyEditor.new())
+             return true # I want this one
+        else:
+             return false
+
+
+Editor
+------
+
+
+Here is an editor for editing integers
+
+.. tabs::
+ .. code-tab:: gdscript GDScript
+    
+    # MyEditor.gd 
+    class_name MyEditor
+
+    var updating = false
+
+    func _spin_changed(value):
+        if (updating):
+            return
+
+        emit_changed( get_property(), value )
+
+    func update_property():
+        var new_value = get_edited_object()[ get_edited_property() ]
+
+        updating=true
+        spin.set_value( new_value )
+        updating=false
+
+    var spin = EditorSpinSlider.new() # use the new spin slider
+    func _init():
+       # if you want to put the editor below the label
+       #   set_bottom_editor( spin )
+       # else use:
+       add_child( spin )
+       # to remember focus when selected back
+       add_focusable( spin ) 
+       spin.set_min(0)
+       spin.set_max(1000)
+       spin.connect("value_changed",self,"_spin_changed")
+     
+
+
+