From 4f6965d39f9fcc0b2eaa4cc97ed096da5c16623d Mon Sep 17 00:00:00 2001
From: ManoloFLTK <41016272+ManoloFLTK@users.noreply.github.com>
Date: Fri, 30 Sep 2022 15:53:05 +0200
Subject: Support of FLTK widgets in OpenGL 3 windows under Windows.

---
 src/Fl_Gl_Choice.cxx      | 12 +++++++++++-
 src/Fl_Gl_Window_Driver.H |  2 --
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/Fl_Gl_Choice.cxx b/src/Fl_Gl_Choice.cxx
index bafab56fd..f67ce0a17 100644
--- a/src/Fl_Gl_Choice.cxx
+++ b/src/Fl_Gl_Choice.cxx
@@ -32,6 +32,17 @@
 // from glew.h in Windows, glext.h in Unix, not used by FLTK's macOS platform
 #  define GL_CURRENT_PROGRAM 0x8B8D
 #endif
+
+// TODO: remove that from this platform-independent source file
+#ifdef _WIN32
+#  include <windows.h> // for WINAPI
+#else
+#  define WINAPI
+#endif
+
+typedef void (WINAPI *glUseProgram_type)(GLint);
+static glUseProgram_type glUseProgram_f = NULL;
+
 GLContext *Fl_Gl_Window_Driver::context_list = 0;
 int Fl_Gl_Window_Driver::nContext = 0;
 static int NContext = 0;
@@ -60,7 +71,6 @@ void Fl_Gl_Window_Driver::del_context(GLContext ctx) {
   if (!nContext) gl_remove_displaylist_fonts();
 }
 
-Fl_Gl_Window_Driver::glUseProgram_type Fl_Gl_Window_Driver::glUseProgram_f = NULL;
 
 void Fl_Gl_Window_Driver::switch_to_GL1() {
   if (!glUseProgram_f) {
diff --git a/src/Fl_Gl_Window_Driver.H b/src/Fl_Gl_Window_Driver.H
index 383b6bf56..5c44a8c32 100644
--- a/src/Fl_Gl_Window_Driver.H
+++ b/src/Fl_Gl_Window_Driver.H
@@ -36,8 +36,6 @@ class Fl_Font_Descriptor;
 class Fl_Gl_Window_Driver {
 private:
   GLint current_prog;
-  typedef void (*glUseProgram_type)(GLint);
-  static glUseProgram_type glUseProgram_f;
 protected:
   Fl_Gl_Window *pWindow;
 public:
-- 
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