From 4a461efae6fa36aeb50e61e381dc2ecf95b83d23 Mon Sep 17 00:00:00 2001
From: Albrecht Schlosser <albrechts.fltk@online.de>
Date: Sat, 25 Nov 2023 20:30:58 +0100
Subject: [PATCH] CMake/Windows/MSVC: Add option to select MSVC Runtime

Selects MSVC compiler/build options known as /MT, /MTd, /MD, or /MDd.

This applies to "Visual Studio" (IDE) and "NMake Makefiles" builds.
---
 CMake/options.cmake | 18 ++++++++++++++++++
 README.CMake.txt    |  5 +++++
 2 files changed, 23 insertions(+)

diff --git a/CMake/options.cmake b/CMake/options.cmake
index 6e2443cfb..5dad843d0 100644
--- a/CMake/options.cmake
+++ b/CMake/options.cmake
@@ -77,6 +77,24 @@ set (OPTION_ABI_VERSION ""
 )
 set (FL_ABI_VERSION ${OPTION_ABI_VERSION})
 
+
+#######################################################################
+#  Select MSVC (Visual Studio) Runtime: DLL (/MDx) or static (/MTx)
+#  where x = 'd' for Debug builds, empty ('') for non-Debug builds.
+#  Note: this might be handled better by the 'MSVC_RUNTIME_LIBRARY'
+#  target property for each target rather than setting a global
+#  CMake variable - but this version does the latter.
+#######################################################################
+
+if (MSVC)
+  option (FLTK_MSVC_RUNTIME_DLL "use MSVC Runtime-DLL (/MDx)" ON)
+  if (FLTK_MSVC_RUNTIME_DLL)
+    set (CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>DLL")
+  else ()
+    set (CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
+  endif ()
+endif (MSVC)
+
 #######################################################################
 #  Bundled Library Options
 #######################################################################
diff --git a/README.CMake.txt b/README.CMake.txt
index 7ada4cefc..c64c0c75c 100644
--- a/README.CMake.txt
+++ b/README.CMake.txt
@@ -133,6 +133,11 @@ FLTK_BUILD_TEST - default ON
 FLTK_BUILD_EXAMPLES - default OFF
    Builds the example programs in the 'examples' directory.
 
+FLTK_MSVC_RUNTIME_DLL - default ON (only for Visual Studio and NMake).
+   Selects whether the build uses the MS runtime DLL or not.
+   Default is ON: either /MD or /MDd for Release or Debug, respectively.
+   Select OFF for either /MT or /MTd for Release or Debug, respectively.
+
 OPTION_CAIRO - default OFF
    Enables support of class Fl_Cairo_Window (all platforms, requires the
    Cairo library) - see README.Cairo.txt.