FindSDL_ttf

定位 SDL_ttf 函式庫

此模組定義了

SDL_TTF_LIBRARIES, the name of the library to link against
SDL_TTF_INCLUDE_DIRS, where to find the headers
SDL_TTF_FOUND, if false, do not try to link against
SDL_TTF_VERSION_STRING - human-readable string containing the version of SDL_ttf

為了向後相容性，也設定了以下變數

SDLTTF_LIBRARY (same value as SDL_TTF_LIBRARIES)
SDLTTF_INCLUDE_DIR (same value as SDL_TTF_INCLUDE_DIRS)
SDLTTF_FOUND (same value as SDL_TTF_FOUND)

$SDLDIR 是一個環境變數，它對應於建置 SDL 時使用的 ./configure --prefix=$SDLDIR。