From 8a2b7c043fe86916d56044d7489f8dce6ed2d479 Mon Sep 17 00:00:00 2001
From: James Le Cuirot <chewi@gentoo.org>
Date: Sun, 27 Feb 2022 14:01:33 +0000
Subject: [PATCH 3/3] Allow building against the system FLTK library

`USE_INTERNAL_FLTK` defaults to true and ignores `USE_INTERNAL_LIBS`
because users are unlikely to have it installed.

Odamex makes of use screen scaling features in FLTK that have not yet
been released. This change therefore checks for the Fl::screen_scale
symbol and skips the associated code if it is absent. In practise, this
only affects the size of the dialog window on HiDPI screens. The game
window is unaffected.

Tested against FLTK 1.3.5 on Gentoo Linux.

(cherry picked from commit 656afab54e30598022f4dd2af298cf6a487a1fe1)
---
 CMakeLists.txt           |  1 +
 client/CMakeLists.txt    | 23 ++++++++++++++++++++++-
 client/gui/gui_boot.cpp  |  2 ++
 libraries/CMakeLists.txt |  2 +-
 4 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9353d0c6b..599b6e85b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,6 +42,7 @@ option(USE_INTERNAL_DEUTEX "Use internal DeuTex" ${USE_INTERNAL_LIBS})
 cmake_dependent_option( USE_INTERNAL_ZLIB "Use internal zlib" ${USE_INTERNAL_LIBS} BUILD_CLIENT 0 )
 cmake_dependent_option( USE_INTERNAL_PNG "Use internal libpng" ${USE_INTERNAL_LIBS} BUILD_CLIENT 0 )
 cmake_dependent_option( USE_INTERNAL_CURL "Use internal libcurl" ${USE_INTERNAL_LIBS} BUILD_CLIENT 0 )
+cmake_dependent_option( USE_INTERNAL_FLTK "Use internal FLTK" 1 BUILD_CLIENT 0 )
 cmake_dependent_option( USE_INTERNAL_JSONCPP "Use internal JsonCpp" 1 BUILD_SERVER 0 )
 cmake_dependent_option( USE_INTERNAL_WXWIDGETS "Use internal wxWidgets" ${USE_INTERNAL_LIBS} BUILD_LAUNCHER 0 )
 cmake_dependent_option( ENABLE_PORTMIDI "Enable portmidi support" 1 BUILD_CLIENT 0 )
diff --git a/client/CMakeLists.txt b/client/CMakeLists.txt
index bd071a7a5..ff1e72ba3 100644
--- a/client/CMakeLists.txt
+++ b/client/CMakeLists.txt
@@ -206,7 +206,28 @@ if(TARGET SDL2::SDL2 OR TARGET SDL::SDL)
   target_link_libraries(odamex ${PNG_LIBRARY} ${ZLIB_LIBRARY} CURL::libcurl)
   if(NOT GCONSOLE)
     target_include_directories(odamex PRIVATE gui)
-    target_link_libraries(odamex fltk fltk_images)
+
+    if(USE_INTERNAL_FLTK)
+      set(FLTK_LIBRARIES fltk fltk_images)
+      set(HAVE_FLTK_SCREEN_SCALE TRUE)
+    else()
+      set(FLTK_SKIP_OPENGL 1)
+      set(FLTK_SKIP_FORMS 1)
+      set(FLTK_SKIP_FLUID 1)
+      find_package(FLTK REQUIRED)
+      target_include_directories(odamex SYSTEM PRIVATE ${FLTK_INCLUDE_DIR})
+
+      include(CheckCXXSymbolExists)
+      set(CMAKE_REQUIRED_INCLUDES ${FLTK_INCLUDE_DIR})
+      set(CMAKE_REQUIRED_LIBRARIES ${FLTK_LIBRARIES})
+      check_cxx_symbol_exists(Fl::screen_scale "FL/Fl.H" HAVE_FLTK_SCREEN_SCALE)
+    endif()
+
+    if(HAVE_FLTK_SCREEN_SCALE)
+      target_compile_definitions(odamex PRIVATE HAVE_FLTK_SCREEN_SCALE)
+    endif()
+
+    target_link_libraries(odamex ${FLTK_LIBRARIES})
   endif()
 
   if(ENABLE_PORTMIDI)
diff --git a/client/gui/gui_boot.cpp b/client/gui/gui_boot.cpp
index f0a0035d1..834038209 100644
--- a/client/gui/gui_boot.cpp
+++ b/client/gui/gui_boot.cpp
@@ -315,12 +315,14 @@ static BootWindow* MakeBootWindow()
  */
 std::string GUI_BootWindow()
 {
+#ifdef HAVE_FLTK_SCREEN_SCALE
 	// Scale according to 1600x900.
 	Fl::screen_scale(0, MAX(Fl::h() / 900.0f, 1.0f));
 
 	// This feature is too clever by half, and in my experience just
 	// deforms the window.
 	Fl::keyboard_screen_scaling(0);
+#endif
 
 	BootWindow* win = MakeBootWindow();
 	win->initWADDirs();
diff --git a/libraries/CMakeLists.txt b/libraries/CMakeLists.txt
index 493d8f12b..a53441d13 100644
--- a/libraries/CMakeLists.txt
+++ b/libraries/CMakeLists.txt
@@ -255,7 +255,7 @@ endif()
 
 ### FLTK (dep: libpng) ###
 
-if(BUILD_CLIENT)
+if(BUILD_CLIENT AND USE_INTERNAL_FLTK)
   message(STATUS "Compiling FLTK...")
 
   set(_FLTK_BUILDGEN_PARAMS
-- 
2.34.1