Add support for tiff and gif format in screensaver (#4250)

frontend/ui/screensaver.lua

@@ -15,6 +15,14 @@ local _ = require("gettext")
 local Screen = Device.screen
 local T = require("ffi/util").template
 
+local screensaver_provider = {
+    ["jpg"] = true,
+    ["jpeg"] = true,
+    ["png"] = true,
+    ["gif"] = true,
+    ["tif"] = true,
+    ["tiff"] = true,
+}
 local default_screensaver_message = _("Sleeping")
 local Screensaver = {}
 
@@ -29,11 +37,8 @@ local function getRandomImage(dir)
     if ok then
         for entry in iter, dir_obj do
             if lfs.attributes(dir .. entry, "mode") == "file" then
-                local extension =
-                    string.lower(string.match(entry, ".+%.([^.]+)") or "")
-                if extension == "jpg"
-                or extension == "jpeg"
-                or extension == "png" then
+                local extension = string.lower(string.match(entry, ".+%.([^.]+)") or "")
+                if screensaver_provider[extension] then
                     i = i + 1
                     pics[i] = entry
                 end
@@ -113,7 +118,7 @@ function Screensaver:chooseFile()
                     file_filter = function(filename)
                         local util = require("util")
                         local suffix = util.getFileNameSuffix(filename)
-                        if suffix == "jpeg" or suffix == "jpg" or suffix == "png" then
+                        if screensaver_provider[suffix] then
                             return true
                         end
                     end,

frontend/ui/widget/imagewidget.lua

@@ -128,7 +128,7 @@ end
 function ImageWidget:_loadfile()
     local itype = string.lower(string.match(self.file, ".+%.([^.]+)") or "")
     if itype == "png" or itype == "jpg" or itype == "jpeg"
-            or itype == "tiff" then
+            or itype == "tiff" or itype == "tif" or itype == "gif" then
         -- In our use cases for files (icons), we either provide width and height,
         -- or just scale_for_dpi, and scale_factor should stay nil.
         -- Other combinations will result in double scaling, and unexpected results.