$NetBSD: patch-CMakeLists.txt,v 1.5 2021/11/16 15:45:01 wiz Exp $

--- CMakeLists.txt.orig	2021-11-09 07:51:28.000000000 +0000
+++ CMakeLists.txt
@@ -262,6 +262,7 @@ if(BUILD_VIEWER)
       set(FLTK_LIBRARIES ${FLTK_LIBRARIES} ${X11_Xrender_LIB})
     endif()
   endif()
+  set(FLTK_LIBRARIES ${FLTK_LIBRARIES} -lpng)
 endif()
 
 # Check for GNUTLS library