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.

3 files changed, 132 insertions, 60 deletions

diff --git a/src/tangara/lua/bridge.cpp b/src/tangara/lua/bridge.cpp
index 0f1e65ac..1c757a22 100644
--- a/src/tangara/lua/bridge.cpp
+++ b/src/tangara/lua/bridge.cpp
@@ -24,6 +24,7 @@
 #include "lua/lua_controls.hpp"
 #include "lua/lua_database.hpp"
 #include "lua/lua_filesystem.hpp"
+#include "lua/lua_font.hpp"
 #include "lua/lua_queue.hpp"
 #include "lua/lua_screen.hpp"
 #include "lua/lua_testing.hpp"
@@ -50,65 +51,6 @@ namespace lua {
 
 static constexpr char kBridgeKey[] = "bridge";
 
-static auto make_font_cb(const char* name) -> const lv_font_t* {
-  // Most Lua file paths start with "//" in order to deal with LVGL's Windows-y
-  // approach to paths. Try to handle such paths correctly so that paths in Lua
-  // code look a bit more consistent.
-  {
-    std::string name_str = name;
-    if (name_str.starts_with("//")) {
-      name++;
-    }
-  }
-
-  // This following is a bit C-brained. Sorry.
-
-  ESP_LOGI(kTag, "load font '%s'", name);
-  FILE* f = fopen(name, "r");
-  if (!f) {
-    return NULL;
-  }
-
-  uint8_t* data = NULL;
-  long len = 0;
-  lv_font_t* font = NULL;
-
-  if (fseek(f, 0, SEEK_END)) {
-    goto fail_with_file;
-  }
-
-  len = ftell(f);
-  if (len <= 0) {
-    goto fail_with_file;
-  }
-
-  if (fseek(f, 0, SEEK_SET)) {
-    goto fail_with_file;
-  }
-
-  data = reinterpret_cast<uint8_t*>(heap_caps_malloc(len, MALLOC_CAP_SPIRAM));
-  if (!data) {
-    goto fail_with_buffer;
-  }
-
-  if (fread(data, 1, len, f) < len) {
-    goto fail_with_buffer;
-  }
-
-  // We can finally start parsing the font!
-  font = lv_binfont_create_from_buffer(data, len);
-
-fail_with_buffer:
-  // LVGL copies the font data out of the buffer, so we don't need to big raw
-  // data alloc after this function returns.
-  heap_caps_free(data);
-
-fail_with_file:
-  fclose(f);
-
-  return font;
-}
-
 static auto delete_font_cb(const lv_font_t* font) -> void {
   // FIXME: luavgl never actually calls this?
 }
@@ -146,7 +88,7 @@ auto Bridge::installBaseModules(lua_State* L) -> void {
 
 auto Bridge::installLvgl(lua_State* L) -> void {
   luavgl_set_pcall(L, CallProtected);
-  luavgl_set_font_extension(L, make_font_cb, delete_font_cb);
+  luavgl_set_font_extension(L, loadFont, delete_font_cb);
   luaL_requiref(L, "lvgl", luaopen_lvgl, true);
   lua_pop(L, 1);
 }
diff --git a/src/tangara/lua/lua_font.cpp b/src/tangara/lua/lua_font.cpp
new file mode 100644
index 00000000..e5913492
--- /dev/null
+++ b/src/tangara/lua/lua_font.cpp
@@ -0,0 +1,115 @@
+/*
+ * Copyright 2024 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include "lua_font.hpp"
+
+#include <cstdint>
+#include <string>
+
+#include "lauxlib.h"
+#include "lua.h"
+#include "lvgl.h"
+
+#include "events/event_queue.hpp"
+#include "lua/bridge.hpp"
+#include "lua/lua_registry.hpp"
+#include "lua/lua_thread.hpp"
+
+namespace lua {
+
+[[maybe_unused]] static constexpr char kTag[] = "lua_font";
+
+/* Reads the given file completely into PSRAM. */
+static auto readFont(std::string path) -> std::span<uint8_t> {
+  // This following is a bit C-brained. Sorry.
+  FILE* f = fopen(path.c_str(), "r");
+  if (!f) {
+    return {};
+  }
+
+  uint8_t* data = NULL;
+  long len = 0;
+
+  if (fseek(f, 0, SEEK_END)) {
+    goto fail;
+  }
+
+  len = ftell(f);
+  if (len <= 0) {
+    goto fail;
+  }
+
+  if (fseek(f, 0, SEEK_SET)) {
+    len = 0;
+    goto fail;
+  }
+
+  data = reinterpret_cast<uint8_t*>(heap_caps_malloc(len, MALLOC_CAP_SPIRAM));
+  if (!data) {
+    len = 0;
+    goto fail;
+  }
+
+  if (fread(data, 1, len, f) < len) {
+    heap_caps_free(data);
+    len = 0;
+  }
+
+fail:
+  fclose(f);
+
+  return {data, static_cast<size_t>(len)};
+}
+
+static auto parseFont(std::span<uint8_t> data) -> lv_font_t* {
+  if (data.empty()) {
+    return nullptr;
+  }
+
+  lv_font_t* font = lv_binfont_create_from_buffer(data.data(), data.size());
+  heap_caps_free(data.data());
+
+  return font;
+}
+
+auto loadFont(lua_State* L, const char* path, int cb_ref) -> void {
+  // Most Lua file paths start with "//" in order to deal with LVGL's Windows-y
+  // approach to paths. Try to handle such paths correctly so that paths in Lua
+  // code look a bit more consistent.
+  std::string path_str = path;
+  if (path_str.starts_with("//")) {
+    path++;
+    path_str = path;
+  }
+
+  // Do the file read from the current thread, since the path might be for a
+  // file in flash, and we can't read from flash in a background task.
+  auto font_data = readFont(path_str);
+
+  Bridge* bridge = Bridge::Get(L);
+  bridge->services().bg_worker().Dispatch<void>([=]() {
+    // Do the parsing now that we're in the background.
+    lv_font_t* font = parseFont(font_data);
+
+    // Hop back to the UI task to invoke the Lua callback.
+    events::Ui().RunOnTask([=] {
+      // Retrieve the callback by ref, and release the ref.
+      lua_rawgeti(L, LUA_REGISTRYINDEX, cb_ref);
+      luaL_unref(L, LUA_REGISTRYINDEX, cb_ref);
+
+      // We always invoke the callback, but we don't always have a result.
+      if (font) {
+        lua_pushlightuserdata(L, (void*)font);
+      } else {
+        lua_pushnil(L);
+      }
+
+      CallProtected(L, 1, 0);
+    });
+  });
+}
+
+}  // namespace lua
diff --git a/src/tangara/lua/lua_font.hpp b/src/tangara/lua/lua_font.hpp
new file mode 100644
index 00000000..dfec4eb0
--- /dev/null
+++ b/src/tangara/lua/lua_font.hpp
@@ -0,0 +1,15 @@
+/*
+ * Copyright 2024 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include "lua.hpp"
+
+namespace lua {
+
+auto loadFont(lua_State* L, const char* name, int cb_ref) -> void;
+
+}