$NetBSD: patch-CMakeLists.txt,v 1.4 2021/05/16 21:06:43 wiz Exp $

--- CMakeLists.txt.orig	2021-04-28 15:26:55.658924359 +0000
+++ CMakeLists.txt
@@ -250,6 +250,7 @@ if(UNIX AND NOT APPLE)
   if(X11_Xrender_FOUND)
     set(FLTK_LIBRARIES ${FLTK_LIBRARIES} ${X11_Xrender_LIB})
   endif()
+  set(FLTK_LIBRARIES ${FLTK_LIBRARIES} -lpng)
 endif()
 
 # Check for GNUTLS library
