add simple checkbox component

druid/base/checkbox.lua

@@ -0,0 +1,44 @@
+--- Druid checkbox component
+-- @module base.checkbox
+
+local helper = require("druid.helper")
+
+local M = {}
+
+
+local function state_animate(node, state)
+	local target = state and 1 or 0
+	gui.animate(node, "color.w", target, gui.EASING_OUTSINE, 0.1)
+end
+
+
+function M.set_state(self, state, is_silence)
+	if self.state == state then
+		return
+	end
+
+	self.state = state
+	state_animate(self.node, state)
+
+	if not is_silence and self.callback then
+		self.callback(self.parent.parent, state)
+	end
+end
+
+
+-- TODO: pass self as first parameter
+local function on_click(context, self)
+	M.set_state(self, not self.state)
+end
+
+
+function M.init(self, node, callback, click_node)
+	self.node = helper.get_node(node)
+	self.click_node = helper.get_node(click_node)
+	self.callback = callback
+	self.button = self.parent:new_button(self.click_node or self.node, on_click, self)
+	M.set_state(self, false, true)
+end
+
+
+return M