From 14e885a54c4cab19011ec10f466fc992f3e03f4e Mon Sep 17 00:00:00 2001
From: Sam Serrels <doogly1@gmail.com>
Date: Mon, 2 Jan 2017 01:36:47 +0000
Subject: [PATCH] Added option to Cmake build allowing a custom location of
 Zlib to be specified. This is useful in a scenario where libpng is being
 built as a subproject alongside zlib by another project..

---
 CMakeLists.txt | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e5d429e9c..5bd8d2803 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -41,8 +41,15 @@ set(PNGLIB_NAME libpng${PNGLIB_MAJOR}${PNGLIB_MINOR})
 set(PNGLIB_VERSION ${PNGLIB_MAJOR}.${PNGLIB_MINOR}.${PNGLIB_RELEASE})
 
 # needed packages
-find_package(ZLIB REQUIRED)
-include_directories(${ZLIB_INCLUDE_DIR})
+
+#Allow users to specify location of Zlib, 
+# Useful if zlib is being built alongside this as a sub-project
+option(PNG_BUILD_ZLIB "Custom zlib Location, else find_package is used" OFF)
+
+IF(NOT PNG_BUILD_ZLIB)
+  find_package(ZLIB REQUIRED)
+  include_directories(${ZLIB_INCLUDE_DIR})
+ENDIF(NOT PNG_BUILD_ZLIB)
 
 if(NOT WIN32)
   find_library(M_LIBRARY