Added material_overlay property to MeshInstance3D

Applying overlay materials into multi-surface meshes currently
requires adding a next pass material to all the surfaces, which
might be cumbersome when the material is to be applied to a range
of different geometries. This also makes it not trivial to use
AnimationPlayer to control the material in case of visual effects.
The material_override property is not an option as it works
replacing the active material for the surfaces, not adding a new pass.

This commit adds the material_overlay property to GeometryInstance3D
(and therefore MeshInstance3D), having the same reach as
material_override (that is, all surfaces) but adding a new material
pass on top of the active materials, instead of replacing them.

1 files changed, 4 insertions, 0 deletions

diff --git a/scene/3d/visual_instance_3d.h b/scene/3d/visual_instance_3d.h
index b08f54b3ec..dd0eb25001 100644
--- a/scene/3d/visual_instance_3d.h
+++ b/scene/3d/visual_instance_3d.h
@@ -110,6 +110,7 @@ public:
 private:
 	ShadowCastingSetting shadow_casting_setting = SHADOW_CASTING_SETTING_ON;
 	Ref<Material> material_override;
+	Ref<Material> material_overlay;
 
 	float visibility_range_begin = 0.0;
 	float visibility_range_end = 0.0;
@@ -164,6 +165,9 @@ public:
 	void set_material_override(const Ref<Material> &p_material);
 	Ref<Material> get_material_override() const;
 
+	void set_material_overlay(const Ref<Material> &p_material);
+	Ref<Material> get_material_overlay() const;
+
 	void set_extra_cull_margin(float p_margin);
 	float get_extra_cull_margin() const;