[libgxps/wip/nacho/visibility: 4/7] nmake: add support to build with libpng support

[Ignacio Casal Quinteiro <icq src gnome org>]

commit ba5557a56906dc08fe3dd4c73cdb798dbfe28c69
Author: Ignacio Casal Quinteiro <ignacio casal nice-software com>
Date:   Fri Sep 9 16:20:16 2016 +0200

    nmake: add support to build with libpng support
    
    https://bugzilla.gnome.org/show_bug.cgi?id=771057

 nmake/config-msvc.mak |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)
---
diff --git a/nmake/config-msvc.mak b/nmake/config-msvc.mak
index 977d75f..6f42be0 100644
--- a/nmake/config-msvc.mak
+++ b/nmake/config-msvc.mak
@@ -3,6 +3,9 @@
 # GLib is required for all utility programs and tests
 GXPS_MAIN_LIBS = gio-2.0.lib gobject-2.0.lib glib-2.0.lib cairo.lib archive.lib freetype.lib
 
+# libpng library
+LIBPNG_LIB = libpng16.lib
+
 # Please do not change anything beneath this line unless maintaining the NMake Makefiles
 # Bare minimum features and sources built into GXPS on Windows
 GXPS_DEFINES = /DGXPS_COMPILATION
@@ -38,6 +41,15 @@ GXPS_DLL_FILENAME = $(CFG)\$(PLAT)\libgxps-0
 GXPS_DLL_FILENAME = $(CFG)\$(PLAT)\gxps-vs$(VSVER)
 !endif
 
+# Enable libpng if desired
+!if "$(LIBPNG)" == "1"
+GXPS_DEFINES = $(GXPS_DEFINES) /DHAVE_LIBPNG=1
+GXPS_DEP_LIBS = $(GXPS_DEP_LIBS) $(LIBPNG_LIB)
+GXPS_CFLAGS = \
+       $(GXPS_CFLAGS) \
+       /I$(PREFIX)\include\libpng
+!endif
+
 EXTRA_TARGETS =
 
 GXPS_TESTS =