feat: initial fft spectrum visualization support

The final goal is actually still clone ShadowPlayer's spectrum
visualization, tho.

CMakeLists.txt

@@ -3,7 +3,8 @@ cmake_minimum_required(VERSION 3.12)
 project(pineapple-music LANGUAGES CXX)
 
 include (GNUInstallDirs)
-include (FeatureSummary)
+include (FeatureSummary)
+include (FetchContent)
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
@@ -18,7 +19,18 @@ option(USE_QTEXTCODEC "Use QTextCodec instead of QStringConverter, in case Qt is
 
 find_package(Qt6 6.6 COMPONENTS Widgets Multimedia Network LinguistTools REQUIRED)
 find_package(TagLib 2.0.0)
-find_package(KF6Codecs 6.1.0)
+find_package(KF6Codecs 6.1.0)
+
+FetchContent_Declare(
+    kissfft
+    GIT_REPOSITORY https://github.com/mborgerding/kissfft.git
+    GIT_TAG f5f2a3b2f2cd02bf80639adb12cbeed125bdf420
+)
+set(KISSFFT_PKGCONFIG OFF CACHE BOOL "dep(kissfft): pkgconfig support")
+set(KISSFFT_STATIC ON CACHE BOOL "dep(kissfft): static linking")
+set(KISSFFT_TEST OFF CACHE BOOL "dep(kissfft): enable testing")
+set(KISSFFT_TOOLS OFF CACHE BOOL "dep(kissfft): build tools")
+FetchContent_MakeAvailable(kissfft)
 
 if (USE_QTEXTCODEC)
     find_package(Qt6 6.6 COMPONENTS Core5Compat REQUIRED)
@@ -31,7 +43,8 @@ set (PMUSIC_CPP_FILES
     playlistmanager.cpp
     singleapplicationmanager.cpp
     lrcbar.cpp
-    lyricsmanager.cpp
+    lyricsmanager.cpp
+    fftspectrum.cpp
 )
 
 set (PMUSIC_HEADER_FILES
@@ -40,7 +53,8 @@ set (PMUSIC_HEADER_FILES
     playlistmanager.h
     singleapplicationmanager.h
     lrcbar.h
-    lyricsmanager.h
+    lyricsmanager.h
+    fftspectrum.h
 )
 
 set (PMUSIC_UI_FILES
@@ -80,7 +94,7 @@ if (TARGET KF6::Codecs)
     target_link_libraries (${EXE_NAME} PRIVATE KF6::Codecs)
 endif ()
 
-target_link_libraries(${EXE_NAME} PRIVATE Qt::Widgets Qt::Multimedia Qt::Network)
+target_link_libraries(${EXE_NAME} PRIVATE Qt::Widgets Qt::Multimedia Qt::Network kissfft::kissfft)
 
 if (USE_QTEXTCODEC)
     target_compile_definitions(${EXE_NAME} PRIVATE USE_QTEXTCODEC=1)