Offer the player a temporary inventory while waiting for master

plugins/inventory_sync/module/gui/progress_dialog.lua

@@ -0,0 +1,71 @@
+-- Show inventory download progressbar
+function open_dialog(player, progress, total)
+    if player.gui.screen.inventory_sync_progress then
+        player.gui.screen.inventory_sync_progress.destroy()
+    end
+    if progress == total then
+        return -- Hide dialog on completed download
+    end
+
+    local frame = player.gui.screen.add {
+        name = "inventory_sync_progress",
+        type = "frame",
+        direction = "vertical",
+    }
+
+    local titlebar = frame.add {
+        type = "flow",
+    }
+    titlebar.drag_target = frame
+
+    local title = titlebar.add {
+        type = "label",
+        style = "frame_title",
+        caption = "Inventory sync",
+    }
+    title.drag_target = frame
+
+    local filler = titlebar.add {
+        type = "empty-widget",
+        style = "draggable_space_header",
+    }
+	filler.style.horizontally_stretchable = "on"
+	filler.style.right_margin = 4
+	filler.style.height = 24
+	filler.drag_target = frame
+
+	titlebar.add {
+		name = "inventory_sync_progress_close_button",
+		type = "sprite-button",
+		sprite = "utility/close_white",
+		hovered_sprite = "utility/close_black",
+		clicked_sprite = "utility/close_black",
+		style = "frame_action_button",
+	}
+
+	local content = frame.add {
+		name = "inventory_sync_progress_dialog_content",
+		type = "frame",
+		direction = "vertical",
+		style = "inside_shallow_frame_with_padding",
+	}
+	content.style.width = 400
+
+	local p1 = content.add {
+		type = "label",
+		caption = "Downloading inventory chunk"..progress.."/"..total,
+	}
+	p1.style.single_line = false
+	p1.style.bottom_margin = 8
+
+    local progressbar = content.add {
+        type = "progressbar",
+        value = progress / total,
+    }
+    progressbar.style.width = 376 -- inside_shallow_frame_with_padding has 12px padding on each side
+
+    frame.force_auto_center()
+    player.opened = frame
+end
+
+return open_dialog