Add support for scene/resource customization in export plugins

EditorExportPlugin adds a set of callbacks to allow customizing scenes, resources or subresources in all files exported:
* Can take scene files, resource files and subresources in all of them.
* Uses a cache for the converted files if nothing changes, so this work only happens if a file is modified.
* Uses hashing to differentiate export configuration caches.
* Removed the previous conversion code to binary, as this one uses existing stuff.

This API is useful in several scenarios:
* Needed by the "server" export platform to get rid of textures, meshes, audio, etc.
* Needed by text to binary converters.
* Needed by eventual optimizations such as shader precompiling on export, mesh merging and optimization, etc.

This is a draft, feedback is very welcome.

3 files changed, 72 insertions, 0 deletions

diff --git a/doc/classes/ConfigFile.xml b/doc/classes/ConfigFile.xml
index d3ad4e6e4b..7ba53f852b 100644
--- a/doc/classes/ConfigFile.xml
+++ b/doc/classes/ConfigFile.xml
@@ -98,6 +98,12 @@
 				Removes the entire contents of the config.
 			</description>
 		</method>
+		<method name="encode_to_text" qualifiers="const">
+			<return type="String" />
+			<description>
+				Obtain the text version of this config file (the same text that would be written to a file).
+			</description>
+		</method>
 		<method name="erase_section">
 			<return type="void" />
 			<param index="0" name="section" type="String" />
diff --git a/doc/classes/EditorExportPlatform.xml b/doc/classes/EditorExportPlatform.xml
new file mode 100644
index 0000000000..1d63af9233
--- /dev/null
+++ b/doc/classes/EditorExportPlatform.xml
@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="EditorExportPlatform" inherits="RefCounted" version="4.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+	<brief_description>
+	</brief_description>
+	<description>
+	</description>
+	<tutorials>
+	</tutorials>
+</class>
diff --git a/doc/classes/EditorExportPlugin.xml b/doc/classes/EditorExportPlugin.xml
index 091bac7d8e..3e8ce10aa5 100644
--- a/doc/classes/EditorExportPlugin.xml
+++ b/doc/classes/EditorExportPlugin.xml
@@ -10,6 +10,51 @@
 	<tutorials>
 	</tutorials>
 	<methods>
+		<method name="_begin_customize_resources" qualifiers="virtual const">
+			<return type="bool" />
+			<param index="0" name="platform" type="EditorExportPlatform" />
+			<param index="1" name="features" type="PackedStringArray" />
+			<description>
+				Return true if this plugin will customize resources based on the platform and features used.
+			</description>
+		</method>
+		<method name="_begin_customize_scenes" qualifiers="virtual const">
+			<return type="bool" />
+			<param index="0" name="platform" type="EditorExportPlatform" />
+			<param index="1" name="features" type="PackedStringArray" />
+			<description>
+				Return true if this plugin will customize scenes based on the platform and features used.
+			</description>
+		</method>
+		<method name="_customize_resource" qualifiers="virtual">
+			<return type="Resource" />
+			<param index="0" name="resource" type="Resource" />
+			<param index="1" name="path" type="String" />
+			<description>
+				Customize a resource. If changes are made to it, return the same or a new resource. Otherwise, return [code]null[/code].
+				The [i]path[/i] argument is only used when customizing an actual file, otherwise this means that this resource is part of another one and it will be empty.
+			</description>
+		</method>
+		<method name="_customize_scene" qualifiers="virtual">
+			<return type="Node" />
+			<param index="0" name="scene" type="Node" />
+			<param index="1" name="path" type="String" />
+			<description>
+				Customize a scene. If changes are made to it, return the same or a new scene. Otherwise, return [code]null[/code]. If a new scene is returned, it is up to you to dispose of the old one.
+			</description>
+		</method>
+		<method name="_end_customize_resources" qualifiers="virtual">
+			<return type="void" />
+			<description>
+				This is called when the customization process for resources ends.
+			</description>
+		</method>
+		<method name="_end_customize_scenes" qualifiers="virtual">
+			<return type="void" />
+			<description>
+				This is called when the customization process for scenes ends.
+			</description>
+		</method>
 		<method name="_export_begin" qualifiers="virtual">
 			<return type="void" />
 			<param index="0" name="features" type="PackedStringArray" />
@@ -36,6 +81,18 @@
 				Calling [method skip] inside this callback will make the file not included in the export.
 			</description>
 		</method>
+		<method name="_get_customization_configuration_hash" qualifiers="virtual const">
+			<return type="int" />
+			<description>
+				Return a hash based on the configuration passed (for both scenes and resources). This helps keep separate caches for separate export configurations.
+			</description>
+		</method>
+		<method name="_get_name" qualifiers="virtual const">
+			<return type="String" />
+			<description>
+				Return the name identifier of this plugin (for future identification by the exporter).
+			</description>
+		</method>
 		<method name="add_file">
 			<return type="void" />
 			<param index="0" name="path" type="String" />