From 2971625418c528e9310d4004bf01bfed7e901eb1 Mon Sep 17 00:00:00 2001
From: Matthias Melcher <github@matthiasm.com>
Date: Mon, 20 Feb 2023 13:40:27 +0100
Subject: Add GLUT_ELAPSED_TIME simulation

---
 FL/glut.H                  |  4 ++--
 src/glut_compatibility.cxx | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/FL/glut.H b/FL/glut.H
index b6e915985..f83231c3a 100644
--- a/FL/glut.H
+++ b/FL/glut.H
@@ -315,12 +315,12 @@ enum {
   GLUT_INIT_WINDOW_HEIGHT,
   GLUT_INIT_DISPLAY_MODE,
   GLUT_WINDOW_BUFFER_SIZE,
-  GLUT_VERSION
+  GLUT_VERSION,
 //GLUT_WINDOW_NUM_CHILDREN,
 //GLUT_WINDOW_CURSOR,
 //GLUT_SCREEN_WIDTH_MM,
 //GLUT_SCREEN_HEIGHT_MM,
-//GLUT_ELAPSED_TIME,
+  GLUT_ELAPSED_TIME,
 };
 
 #  define GLUT_WINDOW_STENCIL_SIZE      GL_STENCIL_BITS
diff --git a/src/glut_compatibility.cxx b/src/glut_compatibility.cxx
index c7484ad5f..adcac1b7a 100644
--- a/src/glut_compatibility.cxx
+++ b/src/glut_compatibility.cxx
@@ -190,8 +190,14 @@ Fl_Glut_Window::Fl_Glut_Window(int X,int Y,int W,int H, const char *t) :
 
 static int initargc;
 static char **initargv;
+static char glut_starttime_set = 0;
+static Fl_Timestamp glut_starttime;
 
 void glutInit(int *argc, char **argv) {
+  if (!glut_starttime_set) {
+    glut_starttime = Fl::now();
+    glut_starttime_set = 1;
+  }
   initargc = *argc;
   initargv = new char*[*argc+1];
   int i,j;
@@ -405,7 +411,12 @@ int glutGet(GLenum type) {
   case GLUT_INIT_WINDOW_WIDTH: return initw;
   case GLUT_INIT_WINDOW_HEIGHT: return inith;
   case GLUT_INIT_DISPLAY_MODE: return glut_mode;
-//case GLUT_ELAPSED_TIME:
+  case GLUT_ELAPSED_TIME:
+      if (!glut_starttime_set) {
+        glut_starttime = Fl::now();
+        glut_starttime_set = 1;
+      }
+      return (int)(Fl::seconds_since(glut_starttime)*1000.0); // milliseconds
   case GLUT_WINDOW_BUFFER_SIZE:
     if (glutGet(GLUT_WINDOW_RGBA))
       return glutGet(GLUT_WINDOW_RED_SIZE)+
-- 
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