Add debug colours and fills to CollisionPolygon3D.

This brings CollisionPolygon3D up to feature parity with its counterpart
CollisionShape3D. Closes #101414.

In addition, adding this feature fixes the issue that CollisionPolygon3D
would never be rendered in exported builds, even if Visible Collision Shapes
is enabled at runtime. Closes #101413.

editor/plugins/gizmos/collision_polygon_3d_gizmo_plugin.cpp

@@ -30,14 +30,44 @@
 
 #include "collision_polygon_3d_gizmo_plugin.h"
 
+#include "core/math/geometry_2d.h"
 #include "scene/3d/physics/collision_polygon_3d.h"
 
 CollisionPolygon3DGizmoPlugin::CollisionPolygon3DGizmoPlugin() {
-	const Color gizmo_color = SceneTree::get_singleton()->get_debug_collisions_color();
-	create_material("shape_material", gizmo_color);
-	const float gizmo_value = gizmo_color.get_v();
-	const Color gizmo_color_disabled = Color(gizmo_value, gizmo_value, gizmo_value, 0.65);
-	create_material("shape_material_disabled", gizmo_color_disabled);
+	create_collision_material("shape_material", 2.0);
+	create_collision_material("shape_material_arraymesh", 0.0625);
+
+	create_collision_material("shape_material_disabled", 0.0625);
+	create_collision_material("shape_material_arraymesh_disabled", 0.015625);
+}
+
+void CollisionPolygon3DGizmoPlugin::create_collision_material(const String &p_name, float p_alpha) {
+	Vector<Ref<StandardMaterial3D>> mats;
+
+	const Color collision_color(1.0, 1.0, 1.0, p_alpha);
+
+	for (int i = 0; i < 4; i++) {
+		bool instantiated = i < 2;
+
+		Ref<StandardMaterial3D> material;
+		material.instantiate();
+
+		Color color = collision_color;
+		color.a *= instantiated ? 0.25 : 1.0;
+
+		material->set_albedo(color);
+		material->set_shading_mode(StandardMaterial3D::SHADING_MODE_UNSHADED);
+		material->set_transparency(StandardMaterial3D::TRANSPARENCY_ALPHA);
+		material->set_render_priority(StandardMaterial3D::RENDER_PRIORITY_MIN + 1);
+		material->set_cull_mode(StandardMaterial3D::CULL_BACK);
+		material->set_flag(StandardMaterial3D::FLAG_DISABLE_FOG, true);
+		material->set_flag(StandardMaterial3D::FLAG_ALBEDO_FROM_VERTEX_COLOR, true);
+		material->set_flag(StandardMaterial3D::FLAG_SRGB_VERTEX_COLOR, true);
+
+		mats.push_back(material);
+	}
+
+	materials[p_name] = mats;
 }
 
 bool CollisionPolygon3DGizmoPlugin::has_gizmo(Node3D *p_spatial) {
@@ -57,6 +87,13 @@ void CollisionPolygon3DGizmoPlugin::redraw(EditorNode3DGizmo *p_gizmo) {
 
 	p_gizmo->clear();
 
+	const Ref<StandardMaterial3D> material =
+			get_material(!polygon->is_disabled() ? "shape_material" : "shape_material_disabled", p_gizmo);
+	const Ref<StandardMaterial3D> material_arraymesh =
+			get_material(!polygon->is_disabled() ? "shape_material_arraymesh" : "shape_material_arraymesh_disabled", p_gizmo);
+
+	const Color collision_color = polygon->is_disabled() ? Color(1.0, 1.0, 1.0, 0.75) : polygon->get_debug_color();
+
 	Vector<Vector2> points = polygon->get_polygon();
 	float depth = polygon->get_depth() * 0.5;
 
@@ -71,9 +108,125 @@ void CollisionPolygon3DGizmoPlugin::redraw(EditorNode3DGizmo *p_gizmo) {
 		lines.push_back(Vector3(points[i].x, points[i].y, -depth));
 	}
 
-	const Ref<Material> material =
-			get_material(!polygon->is_disabled() ? "shape_material" : "shape_material_disabled", p_gizmo);
+	if (polygon->get_debug_fill_enabled()) {
+		Ref<ArrayMesh> array_mesh;
+		array_mesh.instantiate();
 
-	p_gizmo->add_lines(lines, material);
+		Vector<Vector3> verts;
+		Vector<Color> colors;
+		Vector<int> indices;
+
+		// Determine orientation of the 2D polygon's vertices to determine
+		// which direction to draw outer polygons.
+		float signed_area = 0.0f;
+		for (int i = 0; i < points.size(); i++) {
+			const int j = (i + 1) % points.size();
+			signed_area += points[i].x * points[j].y - points[j].x * points[i].y;
+		}
+
+		// Generate triangles for the sides of the extruded polygon.
+		for (int i = 0; i < points.size(); i++) {
+			verts.push_back(Vector3(points[i].x, points[i].y, depth));
+			verts.push_back(Vector3(points[i].x, points[i].y, -depth));
+
+			colors.push_back(collision_color);
+			colors.push_back(collision_color);
+		}
+
+		for (int i = 0; i < verts.size(); i += 2) {
+			const int j = (i + 1) % verts.size();
+			const int k = (i + 2) % verts.size();
+			const int l = (i + 3) % verts.size();
+
+			indices.push_back(i);
+			if (signed_area < 0) {
+				indices.push_back(j);
+				indices.push_back(k);
+			} else {
+				indices.push_back(k);
+				indices.push_back(j);
+			}
+
+			indices.push_back(j);
+			if (signed_area < 0) {
+				indices.push_back(l);
+				indices.push_back(k);
+			} else {
+				indices.push_back(k);
+				indices.push_back(l);
+			}
+		}
+
+		Vector<Vector<Vector2>> decomp = Geometry2D::decompose_polygon_in_convex(polygon->get_polygon());
+
+		// Generate triangles for the bottom cap of the extruded polygon.
+		for (int i = 0; i < decomp.size(); i++) {
+			Vector<Vector3> cap_verts_bottom;
+			Vector<Color> cap_colours_bottom;
+			Vector<int> cap_indices_bottom;
+
+			const int index_offset = verts.size();
+
+			const Vector<Vector2> &convex = decomp[i];
+
+			for (int j = 0; j < convex.size(); j++) {
+				cap_verts_bottom.push_back(Vector3(convex[j].x, convex[j].y, -depth));
+				cap_colours_bottom.push_back(collision_color);
+			}
+
+			if (convex.size() >= 3) {
+				for (int j = 1; j < convex.size(); j++) {
+					const int k = (j + 1) % convex.size();
+
+					cap_indices_bottom.push_back(index_offset + 0);
+					cap_indices_bottom.push_back(index_offset + j);
+					cap_indices_bottom.push_back(index_offset + k);
+				}
+			}
+			verts.append_array(cap_verts_bottom);
+			colors.append_array(cap_colours_bottom);
+			indices.append_array(cap_indices_bottom);
+		}
+
+		// Generate triangles for the top cap of the extruded polygon.
+		for (int i = 0; i < decomp.size(); i++) {
+			Vector<Vector3> cap_verts_top;
+			Vector<Color> cap_colours_top;
+			Vector<int> cap_indices_top;
+
+			const int index_offset = verts.size();
+
+			const Vector<Vector2> &convex = decomp[i];
+
+			for (int j = 0; j < convex.size(); j++) {
+				cap_verts_top.push_back(Vector3(convex[j].x, convex[j].y, depth));
+				cap_colours_top.push_back(collision_color);
+			}
+
+			if (convex.size() >= 3) {
+				for (int j = 1; j < convex.size(); j++) {
+					const int k = (j + 1) % convex.size();
+
+					cap_indices_top.push_back(index_offset + k);
+					cap_indices_top.push_back(index_offset + j);
+					cap_indices_top.push_back(index_offset + 0);
+				}
+			}
+			verts.append_array(cap_verts_top);
+			colors.append_array(cap_colours_top);
+			indices.append_array(cap_indices_top);
+		}
+
+		Array a;
+		a.resize(Mesh::ARRAY_MAX);
+		a[RS::ARRAY_VERTEX] = verts;
+		a[RS::ARRAY_COLOR] = colors;
+		a[RS::ARRAY_INDEX] = indices;
+		array_mesh->add_surface_from_arrays(Mesh::PRIMITIVE_TRIANGLES, a);
+
+		p_gizmo->add_mesh(array_mesh, material_arraymesh);
+	}
+
+	p_gizmo->add_lines(lines, material, false, collision_color);
 	p_gizmo->add_collision_segments(lines);
 }

editor/plugins/gizmos/collision_polygon_3d_gizmo_plugin.h

@@ -36,6 +36,8 @@
 class CollisionPolygon3DGizmoPlugin : public EditorNode3DGizmoPlugin {
 	GDCLASS(CollisionPolygon3DGizmoPlugin, EditorNode3DGizmoPlugin);
 
+	void create_collision_material(const String &p_name, float p_alpha);
+
 public:
 	bool has_gizmo(Node3D *p_spatial) override;
 	String get_gizmo_name() const override;