Implement visibility range and dependencies.

This commit adds the following properties to GeometryInstance3D: `visibility_range_begin`,
`visibility_range_begin_margin`, `visibility_range_end`, `visibility_range_end_margin`.

Together they define a range in which the GeometryInstance3D will be visible from the camera,
taking hysteresis into account for state changes. A begin or end value of 0 will be ignored,
so the visibility range can be open-ended in both directions.

This commit also adds the `visibility_parent` property to 'Node3D'.
Which defines the visibility parents of the node and its subtree (until
another parent is defined).

Visual instances with a visibility parent will only be visible when the parent, and all of its
ancestors recursively, are hidden because they are closer to the camera than their respective
`visibility_range_begin` thresholds.

Combining visibility ranges and visibility parents users can set-up a quick HLOD system
that shows high detail meshes when close (i.e buildings, trees) and merged low detail meshes
for far away groups (i.e. cities, woods).

3 files changed, 41 insertions, 42 deletions

diff --git a/doc/classes/GeometryInstance3D.xml b/doc/classes/GeometryInstance3D.xml
index b2c3bfc3ed..667ca2dacf 100644
--- a/doc/classes/GeometryInstance3D.xml
+++ b/doc/classes/GeometryInstance3D.xml
@@ -52,25 +52,21 @@
 		</member>
 		<member name="lod_bias" type="float" setter="set_lod_bias" getter="get_lod_bias" default="1.0">
 		</member>
-		<member name="lod_max_distance" type="float" setter="set_lod_max_distance" getter="get_lod_max_distance" default="0.0">
-			The GeometryInstance3D's max LOD distance.
-			[b]Note:[/b] This property currently has no effect.
+		<member name="material_override" type="Material" setter="set_material_override" getter="get_material_override">
+			The material override for the whole geometry.
+			If a material is assigned to this property, it will be used instead of any material set in any material slot of the mesh.
 		</member>
-		<member name="lod_max_hysteresis" type="float" setter="set_lod_max_hysteresis" getter="get_lod_max_hysteresis" default="0.0">
-			The GeometryInstance3D's max LOD margin.
-			[b]Note:[/b] This property currently has no effect.
+		<member name="visibility_range_begin" type="float" setter="set_visibility_range_begin" getter="get_visibility_range_begin" default="0.0">
+			Starting distance from which the GeometryInstance3D will be visible, taking [member visibility_range_begin_margin] into account as well. The default value of 0 is used to disable the range check.
 		</member>
-		<member name="lod_min_distance" type="float" setter="set_lod_min_distance" getter="get_lod_min_distance" default="0.0">
-			The GeometryInstance3D's min LOD distance.
-			[b]Note:[/b] This property currently has no effect.
+		<member name="visibility_range_begin_margin" type="float" setter="set_visibility_range_begin_margin" getter="get_visibility_range_begin_margin" default="0.0">
+			Margin for the [member visibility_range_begin] threshold. The GeometryInstance3D will only change its visibility state when it goes over or under the [member visibility_range_begin] threshold by this amount.
 		</member>
-		<member name="lod_min_hysteresis" type="float" setter="set_lod_min_hysteresis" getter="get_lod_min_hysteresis" default="0.0">
-			The GeometryInstance3D's min LOD margin.
-			[b]Note:[/b] This property currently has no effect.
+		<member name="visibility_range_end" type="float" setter="set_visibility_range_end" getter="get_visibility_range_end" default="0.0">
+			Distance from which the GeometryInstance3D will be hidden, taking [member visibility_range_end_margin] into account as well. The default value of 0 is used to disable the range check..
 		</member>
-		<member name="material_override" type="Material" setter="set_material_override" getter="get_material_override">
-			The material override for the whole geometry.
-			If a material is assigned to this property, it will be used instead of any material set in any material slot of the mesh.
+		<member name="visibility_range_end_margin" type="float" setter="set_visibility_range_end_margin" getter="get_visibility_range_end_margin" default="0.0">
+			Margin for the [member visibility_range_end] threshold. The GeometryInstance3D will only change its visibility state when it goes over or under the [member visibility_range_end] threshold by this amount.
 		</member>
 	</members>
 	<constants>
diff --git a/doc/classes/Node3D.xml b/doc/classes/Node3D.xml
index a6237708c6..ed1899ca74 100644
--- a/doc/classes/Node3D.xml
+++ b/doc/classes/Node3D.xml
@@ -310,6 +310,9 @@
 		<member name="transform" type="Transform3D" setter="set_transform" getter="get_transform" default="Transform3D( 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0 )">
 			Local space [Transform3D] of this node, with respect to the parent node.
 		</member>
+		<member name="visibility_parent" type="NodePath" setter="set_visibility_parent" getter="get_visibility_parent" default="NodePath(&quot;&quot;)">
+			Defines the visibility range parent for this node and its subtree. The visibility parent must be a GeometryInstance3D. Any visual instance will only be visible if the visibility parent (and all of its visibility ancestors) is hidden by being closer to the camera than its own [member GeometryInstance3D.visibility_range_begin]. Nodes hidden via the [member Node3D.visible] property are essentially removed from the visibility dependency tree, so dependant instances will not take the hidden node or its ancestors into account.
+		</member>
 		<member name="visible" type="bool" setter="set_visible" getter="is_visible" default="true">
 			If [code]true[/code], this node is drawn. The node is only visible if all of its antecedents are visible as well (in other words, [method is_visible_in_tree] must return [code]true[/code]).
 		</member>
diff --git a/doc/classes/RenderingServer.xml b/doc/classes/RenderingServer.xml
index ba19176788..9b9644093f 100644
--- a/doc/classes/RenderingServer.xml
+++ b/doc/classes/RenderingServer.xml
@@ -1175,17 +1175,6 @@
 				Once finished with your RID, you will want to free the RID using the RenderingServer's [method free_rid] static method.
 			</description>
 		</method>
-		<method name="instance_geometry_set_as_instance_lod">
-			<return type="void">
-			</return>
-			<argument index="0" name="instance" type="RID">
-			</argument>
-			<argument index="1" name="as_lod_of_instance" type="RID">
-			</argument>
-			<description>
-				Not implemented in Godot 3.x.
-			</description>
-		</method>
 		<method name="instance_geometry_set_cast_shadows_setting">
 			<return type="void">
 			</return>
@@ -1197,45 +1186,45 @@
 				Sets the shadow casting setting to one of [enum ShadowCastingSetting]. Equivalent to [member GeometryInstance3D.cast_shadow].
 			</description>
 		</method>
-		<method name="instance_geometry_set_draw_range">
+		<method name="instance_geometry_set_flag">
 			<return type="void">
 			</return>
 			<argument index="0" name="instance" type="RID">
 			</argument>
-			<argument index="1" name="min" type="float">
-			</argument>
-			<argument index="2" name="max" type="float">
-			</argument>
-			<argument index="3" name="min_margin" type="float">
+			<argument index="1" name="flag" type="int" enum="RenderingServer.InstanceFlags">
 			</argument>
-			<argument index="4" name="max_margin" type="float">
+			<argument index="2" name="enabled" type="bool">
 			</argument>
 			<description>
-				Not implemented in Godot 3.x.
+				Sets the flag for a given [enum InstanceFlags]. See [enum InstanceFlags] for more details.
 			</description>
 		</method>
-		<method name="instance_geometry_set_flag">
+		<method name="instance_geometry_set_material_override">
 			<return type="void">
 			</return>
 			<argument index="0" name="instance" type="RID">
 			</argument>
-			<argument index="1" name="flag" type="int" enum="RenderingServer.InstanceFlags">
-			</argument>
-			<argument index="2" name="enabled" type="bool">
+			<argument index="1" name="material" type="RID">
 			</argument>
 			<description>
-				Sets the flag for a given [enum InstanceFlags]. See [enum InstanceFlags] for more details.
+				Sets a material that will override the material for all surfaces on the mesh associated with this instance. Equivalent to [member GeometryInstance3D.material_override].
 			</description>
 		</method>
-		<method name="instance_geometry_set_material_override">
+		<method name="instance_geometry_set_visibility_range">
 			<return type="void">
 			</return>
 			<argument index="0" name="instance" type="RID">
 			</argument>
-			<argument index="1" name="material" type="RID">
+			<argument index="1" name="min" type="float">
+			</argument>
+			<argument index="2" name="max" type="float">
+			</argument>
+			<argument index="3" name="min_margin" type="float">
+			</argument>
+			<argument index="4" name="max_margin" type="float">
 			</argument>
 			<description>
-				Sets a material that will override the material for all surfaces on the mesh associated with this instance. Equivalent to [member GeometryInstance3D.material_override].
+				Sets the visibility range values for the given geometry instance. Equivalent to [member GeometryInstance3D.visibility_range_begin] and related properties.
 			</description>
 		</method>
 		<method name="instance_set_base">
@@ -1341,6 +1330,17 @@
 				Sets the world space transform of the instance. Equivalent to [member Node3D.transform].
 			</description>
 		</method>
+		<method name="instance_set_visibility_parent">
+			<return type="void">
+			</return>
+			<argument index="0" name="instance" type="RID">
+			</argument>
+			<argument index="1" name="parent" type="RID">
+			</argument>
+			<description>
+				Sets the visibility parent for the given instance. Equivalent to [member Node3D.visibility_parent].
+			</description>
+		</method>
 		<method name="instance_set_visible">
 			<return type="void">
 			</return>