Load fonts asynchronously on a bg task

This saves a second or two from bootup; AFAICT this *mostly* reclaims
the dynamic fonts boot time regression.

1 files changed, 33 insertions, 3 deletions

diff --git a/lua/font.lua b/lua/font.lua
index 7afa1e01..c76602ec 100644
--- a/lua/font.lua
+++ b/lua/font.lua
@@ -1,6 +1,36 @@
 local lvgl = require("lvgl")
 
-return {
-  fusion_12 = lvgl.Font("//lua/fonts/fusion12"),
-  fusion_10 = lvgl.Font("//lua/fonts/fusion10"),
+local fonts = {}
+local fonts_priv = {
+  has_invoked_cb = false,
+  cb = nil,
 }
+
+function fonts_priv.has_loaded_all()
+  return fonts.fusion_12 and fonts.fusion_10
+end
+
+function fonts_priv.invoke_cb()
+  if fonts_priv.has_invoked_cb or not fonts_priv.cb then return end
+  if not fonts_priv.has_loaded_all() then return end
+  fonts_priv.has_invoked_cb = true
+  fonts_priv.cb()
+end
+
+lvgl.Font("//lua/fonts/fusion12", function(font)
+  fonts.fusion_12 = font
+  fonts_priv.invoke_cb()
+end)
+
+lvgl.Font("//lua/fonts/fusion10", function(font)
+  fonts.fusion_10 = font
+  fonts_priv.invoke_cb()
+end)
+
+function fonts.on_loaded(cb)
+  fonts_priv.cb = cb
+  fonts_priv.has_invoked_cb = false
+  fonts_priv.invoke_cb()
+end
+
+return fonts