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, 115 insertions, 0 deletions

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