[gegl] Extend configure checks with checks for SDL2

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 9fb676ae9a26a6ebb21e16d7e350b419a1eb4af7
Author: Stefan Brüns <stefan bruens rwth-aachen de>
Date:   Sun Aug 4 17:55:20 2019 +0200

    Extend configure checks with checks for SDL2
    
    Check for SDL2 first, and iff not found check
    for SDL 1.2. As both library versions define the
    same symbols both are exclusive.

 configure.ac | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 974113404..6e42abd2a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -57,6 +57,7 @@ m4_define([popplerglib_required_version], [0.71.0])
 m4_define([zlib_required_version], [1.2.0])
 m4_define([png_required_version], [1.6.0])
 m4_define([sdl_required_version], [1.2.0])
+m4_define([sdl2_required_version], [2.0.5])
 m4_define([libtiff_required_version], [4.0.0])
 m4_define([webp_required_version], [0.5.0])
 m4_define([poly2tri-c_required_version], [0.0.0])
@@ -948,14 +949,36 @@ AC_SUBST(OPENEXR_CFLAGS)
 AC_SUBST(OPENEXR_LIBS) 
 
 
-###############
-# Check for SDL
-###############
+######################
+# Check for SDL2 / SDL
+######################
 
+AC_ARG_WITH(sdl, [  --without-sdl2          build without SDL2 support])
 AC_ARG_WITH(sdl, [  --without-sdl           build without SDL support])
 
+have_sdl2="no"
+if test "x$with_sdl2" != "xno"; then
+  AC_PATH_PROG(SDL2_CONFIG, sdl2-config, no)
+  if test "$SDL2_CONFIG" = "no"; then
+    have_sdl2="no  (SDL2 library not found)"
+    AC_MSG_RESULT([*** Check for SDL2 library failed.])
+  else
+    have_sdl2="yes"
+    SDL2_CFLAGS=`$SDL2_CONFIG --cflags`
+    SDL2_LIBS=`$SDL2_CONFIG --libs`
+  fi
+fi
+
+AM_CONDITIONAL(HAVE_SDL2, test "$have_sdl2" = "yes")
+
+AC_SUBST(SDL2_CFLAGS)
+AC_SUBST(SDL2_LIBS)
+
 have_sdl="no"
-if test "x$with_sdl" != "xno"; then
+if test "$have_sdl2" = "yes"; then
+  AC_MSG_NOTICE([Skipping SDL check (SDL2 and SDL are exclusive)])
+  have_sdl="no (skipped)"
+elif test "x$with_sdl" != "xno"; then
   AC_PATH_PROG(SDL_CONFIG, sdl-config, no)
   if test "$SDL_CONFIG" = "no"; then
     have_sdl="no  (SDL library not found)"
@@ -968,7 +991,7 @@ if test "x$with_sdl" != "xno"; then
 fi
 
 AM_CONDITIONAL(HAVE_SDL, test "$have_sdl" = "yes")
- 
+
 AC_SUBST(SDL_CFLAGS)
 AC_SUBST(SDL_LIBS)
 
@@ -1417,6 +1440,7 @@ Optional dependencies:
   PNG:             $have_libpng
   OpenEXR:         $have_openexr
   rsvg:            $have_librsvg
+  SDL2:            $have_sdl2
   SDL:             $have_sdl
   libraw:          $have_libraw
   Jasper:          $have_jasper