Godot TreeItem Highlight Code

tree-item-highlight.gd

func _on_Tree_gui_input(event):
	if event is InputEventMouseMotion:
		$Bar.rect_position = Vector2(2, get_y(event.position.y))
		$Bar.rect_size = Vector2(rect_size.x - 12, 17)


func get_y(y):
	var step = 22
	var dy = tree.get_scroll().y
	return floor(y / step) * step + 7 - dy + step * floor(dy / step)


func _on_Tree_mouse_exited():
	$Bar.hide()


func _on_Tree_mouse_entered():
	$Bar.show()

The Bar is a ColorRect with a material shader that makes the background area brighter.

`shader_type canvas_item;

void fragment() {
vec3 c = textureLod(SCREEN_TEXTURE, SCREEN_UV, 0.0).rgb;
if (c.r < 0.3 || c.g < 0.3 || c.b < 0.3) c *= 1.2;
COLOR.rgb = c;
}`