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).

1 files changed, 18 insertions, 12 deletions

diff --git a/scene/3d/visual_instance_3d.h b/scene/3d/visual_instance_3d.h
index 68d29ef81e..2d5699859b 100644
--- a/scene/3d/visual_instance_3d.h
+++ b/scene/3d/visual_instance_3d.h
@@ -107,10 +107,13 @@ public:
 private:
 	ShadowCastingSetting shadow_casting_setting = SHADOW_CASTING_SETTING_ON;
 	Ref<Material> material_override;
-	float lod_min_distance = 0.0;
-	float lod_max_distance = 0.0;
-	float lod_min_hysteresis = 0.0;
-	float lod_max_hysteresis = 0.0;
+
+	float visibility_range_begin = 0.0;
+	float visibility_range_end = 0.0;
+	float visibility_range_begin_margin = 0.0;
+	float visibility_range_end_margin = 0.0;
+
+	Vector<NodePath> visibility_range_children;
 
 	float lod_bias = 1.0;
 
@@ -136,17 +139,20 @@ public:
 	void set_cast_shadows_setting(ShadowCastingSetting p_shadow_casting_setting);
 	ShadowCastingSetting get_cast_shadows_setting() const;
 
-	void set_lod_min_distance(float p_dist);
-	float get_lod_min_distance() const;
+	void set_visibility_range_begin(float p_dist);
+	float get_visibility_range_begin() const;
+
+	void set_visibility_range_end(float p_dist);
+	float get_visibility_range_end() const;
 
-	void set_lod_max_distance(float p_dist);
-	float get_lod_max_distance() const;
+	void set_visibility_range_begin_margin(float p_dist);
+	float get_visibility_range_begin_margin() const;
 
-	void set_lod_min_hysteresis(float p_dist);
-	float get_lod_min_hysteresis() const;
+	void set_visibility_range_end_margin(float p_dist);
+	float get_visibility_range_end_margin() const;
 
-	void set_lod_max_hysteresis(float p_dist);
-	float get_lod_max_hysteresis() const;
+	void set_visibility_range_parent(const Node *p_parent);
+	void clear_visibility_range_parent();
 
 	void set_material_override(const Ref<Material> &p_material);
 	Ref<Material> get_material_override() const;