commit 0627213a824388321b8b39ff2476f5dc04f56638
Author:     ManoloFLTK <41016272+ManoloFLTK@users.noreply.github.com>
AuthorDate: Fri Sep 30 19:25:23 2022 +0200
Commit:     ManoloFLTK <41016272+ManoloFLTK@users.noreply.github.com>
CommitDate: Fri Sep 30 19:25:23 2022 +0200

    FLTK widgets in OpenGL 3 windows: rewrite for driver system.

 src/Fl_Gl_Choice.cxx                              |  9 +--------
 src/Fl_Gl_Window_Driver.H                         |  3 +--
 src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.H   |  2 ++
 src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.cxx | 20 ++++++++++++++++++++
 4 files changed, 24 insertions(+), 10 deletions(-)

diff --git src/Fl_Gl_Choice.cxx src/Fl_Gl_Choice.cxx
index f67ce0a..5c77e97 100644
--- src/Fl_Gl_Choice.cxx
+++ src/Fl_Gl_Choice.cxx
@@ -33,14 +33,7 @@
 #  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);
+typedef void (*glUseProgram_type)(GLint);
 static glUseProgram_type glUseProgram_f = NULL;
 
 GLContext *Fl_Gl_Window_Driver::context_list = 0;
diff --git src/Fl_Gl_Window_Driver.H src/Fl_Gl_Window_Driver.H
index 5c44a8c..0580e52 100644
--- src/Fl_Gl_Window_Driver.H
+++ src/Fl_Gl_Window_Driver.H
@@ -34,9 +34,8 @@ class Fl_Font_Descriptor;
  platform-specific derived class from this class.
  */
 class Fl_Gl_Window_Driver {
-private:
-  GLint current_prog;
 protected:
+  GLint current_prog;
   Fl_Gl_Window *pWindow;
 public:
   static GLContext cached_context;
diff --git src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.H src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.H
index 3b09c73..2de50eb 100644
--- src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.H
+++ src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.H
@@ -51,6 +51,8 @@ class Fl_WinAPI_Gl_Window_Driver : public Fl_Gl_Window_Driver {
   virtual void gl_bitmap_font(Fl_Font_Descriptor *fl_fontsize);
   virtual void get_list(Fl_Font_Descriptor *fd, int r);
   virtual int genlistsize();
+  virtual void switch_to_GL1();
+  virtual void switch_back();
 #if HAVE_GL_OVERLAY
   virtual void gl_hide_before(void *& overlay);
   virtual int can_do_overlay();
diff --git src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.cxx src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.cxx
index 7952dfd..ca72d3e 100644
--- src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.cxx
+++ src/drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.cxx
@@ -25,6 +25,10 @@
 #include "../GDI/Fl_Font.H"
 extern void fl_save_dc(HWND, HDC);
 
+#ifndef GL_CURRENT_PROGRAM
+#  define GL_CURRENT_PROGRAM 0x8B8D // from glew.h
+#endif
+
 // STR #3119: select pixel format with composition support
 // ... and no more than 32 color bits (8 bits/color)
 // Ref: PixelFormatDescriptor Object
@@ -368,6 +372,22 @@ void Fl_WinAPI_Gl_Window_Driver::get_list(Fl_Font_Descriptor *fd, int r) {
 }
 
 
+typedef void (WINAPI *glUseProgram_type)(GLint);
+static glUseProgram_type glUseProgram_f = NULL;
+
+void Fl_WinAPI_Gl_Window_Driver::switch_to_GL1() {
+  if (!glUseProgram_f) {
+    glUseProgram_f = (glUseProgram_type)GetProcAddress("glUseProgram");
+  }
+  glGetIntegerv(GL_CURRENT_PROGRAM, &current_prog);
+  if (current_prog) glUseProgram_f(0);
+}
+
+void Fl_WinAPI_Gl_Window_Driver::switch_back() {
+  if (current_prog) glUseProgram_f((GLuint)current_prog);
+}
+
+
 FL_EXPORT HGLRC fl_win32_glcontext(GLContext rc) { return (HGLRC)rc; }
 
 #endif // HAVE_GL