replace glowstone texture with a new animated one

df_underworld_items/glow_stone.lua

@@ -7,7 +7,18 @@ local glowstone_def = {
 	_doc_items_usagehelp = df_underworld_items.doc.glowstone_usage,
 	light_source = minetest.LIGHT_MAX,
 	description = S("Lightseam"),
-	tiles = {"dfcaverns_glowstone.png"},
+	tiles = {
+		{
+			name = "dfcaverns_glowstone_anim.png",
+			backface_culling = true,
+			animation = {
+				type = "vertical_frames",
+				aspect_w = 16,
+				aspect_h = 16,
+				length = 8,
+			},
+		},
+	},
 	is_ground_content = false,
 	groups = {cracky=3},
 	sounds = default.node_sound_glass_defaults(),

df_underworld_items/textures/license.txt

@@ -2,4 +2,6 @@ All textures not specifically listed here are created by FaceDeer and released u
 
 dfcaverns_glow_amethyst, dfcaverns_glow_amethist_ore - from caverealms glow_amethyst
 
-dfcaverns_slade, dfcaverns_slade_sand, dfcaverns_slade_brick, dfcaverns_glowstone, are all from the Nether mod by PilzAdam: Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) http://creativecommons.org/licenses/by-sa/3.0/
+dfcaverns_slade, dfcaverns_slade_sand, dfcaverns_slade_brick, are all from the Nether mod by PilzAdam: Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) http://creativecommons.org/licenses/by-sa/3.0/
+
+dfcaverns_glowstone_anim is derived from an animated gif of the Sun's surface released by the National Science Foundation under the public domain