Implement distance fade and transparency

The built-in ALPHA in spatial shaders comes pre-set with a per-instance
transparency value. Multiply by it if you want to keep it.

The transparency value of any given GeometryInstance3D is affected by:
   - Its new "transparency" property.
   - Its own visiblity range when the new "visibility_range_fade_mode"
     property is set to "Self".
   - Its parent visibility range when the parent's fade mode is
     set to "Dependencies".

The "Self" mode will fade-out the instance when reaching the visibility
range limits, while the "Dependencies" mode will fade-in its
dependencies.

Per-instance transparency is only implemented in the forward clustered
renderer, support for mobile should be added in the future.

Co-authored-by: reduz <reduzio@gmail.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/scene/3d/visual_instance_3d.h b/scene/3d/visual_instance_3d.h
index 8d24e13d47..acdbc4666a 100644
--- a/scene/3d/visual_instance_3d.h
+++ b/scene/3d/visual_instance_3d.h
@@ -101,6 +101,12 @@ public:
 		LIGHTMAP_SCALE_MAX,
 	};
 
+	enum VisibilityRangeFadeMode {
+		VISIBILITY_RANGE_FADE_DISABLED = RS::VISIBILITY_RANGE_FADE_DISABLED,
+		VISIBILITY_RANGE_FADE_SELF = RS::VISIBILITY_RANGE_FADE_SELF,
+		VISIBILITY_RANGE_FADE_DEPENDENCIES = RS::VISIBILITY_RANGE_FADE_DEPENDENCIES,
+	};
+
 private:
 	ShadowCastingSetting shadow_casting_setting = SHADOW_CASTING_SETTING_ON;
 	Ref<Material> material_override;
@@ -109,8 +115,9 @@ private:
 	float visibility_range_end = 0.0;
 	float visibility_range_begin_margin = 0.0;
 	float visibility_range_end_margin = 0.0;
+	VisibilityRangeFadeMode visibility_range_fade_mode = VISIBILITY_RANGE_FADE_DISABLED;
 
-	Vector<NodePath> visibility_range_children;
+	float transparency = 0.0f;
 
 	float lod_bias = 1.0;
 
@@ -136,6 +143,9 @@ public:
 	void set_cast_shadows_setting(ShadowCastingSetting p_shadow_casting_setting);
 	ShadowCastingSetting get_cast_shadows_setting() const;
 
+	void set_transparecy(float p_transparency);
+	float get_transparency() const;
+
 	void set_visibility_range_begin(float p_dist);
 	float get_visibility_range_begin() const;
 
@@ -148,8 +158,8 @@ public:
 	void set_visibility_range_end_margin(float p_dist);
 	float get_visibility_range_end_margin() const;
 
-	void set_visibility_range_parent(const Node *p_parent);
-	void clear_visibility_range_parent();
+	void set_visibility_range_fade_mode(VisibilityRangeFadeMode p_mode);
+	VisibilityRangeFadeMode get_visibility_range_fade_mode() const;
 
 	void set_material_override(const Ref<Material> &p_material);
 	Ref<Material> get_material_override() const;
@@ -181,5 +191,6 @@ public:
 VARIANT_ENUM_CAST(GeometryInstance3D::ShadowCastingSetting);
 VARIANT_ENUM_CAST(GeometryInstance3D::LightmapScale);
 VARIANT_ENUM_CAST(GeometryInstance3D::GIMode);
+VARIANT_ENUM_CAST(GeometryInstance3D::VisibilityRangeFadeMode);
 
 #endif