From cc6a7d008b402e5e019237e2576e3d98e815bf91 Mon Sep 17 00:00:00 2001
From: Albrecht Schlosser <albrechts.fltk@online.de>
Date: Mon, 4 Apr 2022 21:10:25 +0200
Subject: [PATCH] Remove obsolete config variable 'HAVE_LIBPNG_PNG_H'

This variable has never been used in the code. Configure and CMake
look for a *working* libpng (HAVE_PNG) and set variable HAVE_PNG_H
if the header <png.h> can be included.

The alternative to include <libpng/png.h> is always used in the #else
clause and doesn't need its own config variable. Configure and CMake
log what they find, hence this extra variable is not necessary.
---
 CMake/options.cmake | 16 ++++++----------
 configh.cmake.in    |  4 +++-
 configh.in          |  4 +++-
 configure.ac        |  2 --
 4 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/CMake/options.cmake b/CMake/options.cmake
index ac6f313b5..1d7c08dd3 100644
--- a/CMake/options.cmake
+++ b/CMake/options.cmake
@@ -444,19 +444,16 @@ if (OPTION_USE_SYSTEM_LIBPNG AND PNG_FOUND)
   set (_INCLUDE_SAVED ${CMAKE_REQUIRED_INCLUDES})
   list (APPEND CMAKE_REQUIRED_INCLUDES ${PNG_INCLUDE_DIRS})
 
-  # FIXME - Force search! Maybe use cache to check for option changes?
+  # Note: we do not check for <libpng/png.h> explicitly.
+  # This is assumed to exist if we have PNG_FOUND and don't find <png.h>
 
-  unset (HAVE_PNG_H CACHE)
-  unset (HAVE_LIBPNG_PNG_H CACHE)
+  # FIXME - Force search by unsetting the chache variable. Maybe use
+  # FIXME - another cache variable to check for option changes?
 
-  check_include_files (png.h HAVE_PNG_H)
+  unset (HAVE_PNG_H CACHE) # force search
+  check_include_file (png.h HAVE_PNG_H)
   mark_as_advanced (HAVE_PNG_H)
 
-  if (NOT HAVE_PNG_H)
-    check_include_files (libpng/png.h HAVE_LIBPNG_PNG_H)
-    mark_as_advanced (HAVE_LIBPNG_PNG_H)
-endif ()
-
   set (CMAKE_REQUIRED_INCLUDES ${_INCLUDE_SAVED})
   unset (_INCLUDE_SAVED)
 
@@ -472,7 +469,6 @@ else ()
   set (HAVE_PNG_H 1)
   set (HAVE_PNG_GET_VALID 1)
   set (HAVE_PNG_SET_TRNS_TO_ALPHA 1)
-  set (HAVE_LIBPNG_PNG_H 0)
   include_directories (${CMAKE_CURRENT_SOURCE_DIR}/png)
 endif ()
 
diff --git a/configh.cmake.in b/configh.cmake.in
index cf537af82..dde9ee40a 100644
--- a/configh.cmake.in
+++ b/configh.cmake.in
@@ -260,10 +260,12 @@
 
 /*
  * Which header file do we include for libpng?
+ *   ifdef HAVE_PNG_H : <png.h>
+ *   else             : <libpng/png.h>
+ * There is no other choice.
  */
 
 #cmakedefine HAVE_PNG_H 1
-#cmakedefine HAVE_LIBPNG_PNG_H 1
 
 /*
  * Do we have the png_xyz() functions?
diff --git a/configh.in b/configh.in
index 86e6897c6..e45061b31 100644
--- a/configh.in
+++ b/configh.in
@@ -259,10 +259,12 @@
 
 /*
  * Which header file do we include for libpng?
+ *   ifdef HAVE_PNG_H : <png.h>
+ *   else             : <libpng/png.h>
+ * There is no other choice.
  */
 
 #undef HAVE_PNG_H
-#undef HAVE_LIBPNG_PNG_H
 
 /*
  * Do we have the png_xyz() functions?
diff --git a/configure.ac b/configure.ac
index 2f9d83126..ca2a7bcc2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -738,7 +738,6 @@ AS_IF([test x$enable_localpng != xyes], [
             syspnginc_ok=yes
         ])
         AC_CHECK_HEADER([libpng/png.h], [
-            AC_DEFINE([HAVE_LIBPNG_PNG_H])
             syspnginc_ok=yes
         ])
         AS_IF([test x$syspnginc_ok = xyes], [
@@ -815,7 +814,6 @@ AC_SUBST([JPEGINC])
 AC_SUBST([PNG])
 AC_SUBST([PNGINC])
 AC_SUBST([HAVE_PNG_H])
-AC_SUBST([HAVE_LIBPNG_H])
 AC_SUBST([ZLIB])
 AC_SUBST([ZLIBINC])