Fixed bug 1946 - OpenGL contexts in threads

The SDL OpenGL context code is now properly thread aware.  There are two new functions which return the current OpenGL window and context for the current thread.

There are still places in the cocoa driver where the OpenGL context needs to be updated when the view changes.  These will need a different solution and still use the last globally set context to avoid changing behavior.

include/SDL_video.h

@@ -889,6 +889,16 @@ extern DECLSPEC SDL_GLContext SDLCALL SDL_GL_CreateContext(SDL_Window *
 extern DECLSPEC int SDLCALL SDL_GL_MakeCurrent(SDL_Window * window,
                                                SDL_GLContext context);
 
+/**
+ *  \brief Get the currently active OpenGL window.
+ */
+extern DECLSPEC SDL_Window* SDLCALL SDL_GL_GetCurrentWindow(void);
+
+/**
+ *  \brief Get the currently active OpenGL context.
+ */
+extern DECLSPEC SDL_GLContext SDLCALL SDL_GL_GetCurrentContext(void);
+
 /**
  *  \brief Set the swap interval for the current OpenGL context.
  *

src/video/SDL_sysvideo.h

@@ -302,7 +302,8 @@ struct SDL_VideoDevice
     /* Cache current GL context; don't call the OS when it hasn't changed. */
     SDL_Window *current_glwin;
     SDL_GLContext current_glctx;
-    SDL_threadID current_glthread;
+    SDL_TLSID current_glwin_tls;
+    SDL_TLSID current_glctx_tls;
 
     /* * * */
     /* Data private to this driver */

src/video/SDL_video.c

@@ -500,6 +500,9 @@ SDL_VideoInit(const char *driver_name)
     _this->gl_config.profile_mask = 0;
     _this->gl_config.share_with_current_context = 0;
 
+    _this->current_glwin_tls = SDL_TLSCreate();
+    _this->current_glctx_tls = SDL_TLSCreate();
+
     /* Initialize the video subsystem */
     if (_this->VideoInit(_this) < 0) {
         SDL_VideoQuit();
@@ -2738,7 +2741,8 @@ SDL_GL_CreateContext(SDL_Window * window)
     /* Creating a context is assumed to make it current in the SDL driver. */
     _this->current_glwin = window;
     _this->current_glctx = ctx;
-    _this->current_glthread = SDL_ThreadID();
+    SDL_TLSSet(_this->current_glwin_tls, window, NULL);
+    SDL_TLSSet(_this->current_glctx_tls, ctx, NULL);
 
     return ctx;
 }
@@ -2747,7 +2751,12 @@ int
 SDL_GL_MakeCurrent(SDL_Window * window, SDL_GLContext ctx)
 {
     int retval;
-    SDL_threadID thread = SDL_ThreadID();
+
+    if (window == SDL_GL_GetCurrentWindow() &&
+        ctx == SDL_GL_GetCurrentContext()) {
+        /* We're already current. */
+        return 0;
+    }
 
     if (!ctx) {
         window = NULL;
@@ -2759,26 +2768,42 @@ SDL_GL_MakeCurrent(SDL_Window * window, SDL_GLContext ctx)
         }
     }
 
-    if ((window == _this->current_glwin) && (ctx == _this->current_glctx) && (thread == _this->current_glthread)) {
-        retval = 0;  /* we're already current. */
-    } else {
-        retval = _this->GL_MakeCurrent(_this, window, ctx);
-        if (retval == 0) {
-            _this->current_glwin = window;
-            _this->current_glctx = ctx;
-            _this->current_glthread = thread;
-        }
+    retval = _this->GL_MakeCurrent(_this, window, ctx);
+    if (retval == 0) {
+        _this->current_glwin = window;
+        _this->current_glctx = ctx;
+        SDL_TLSSet(_this->current_glwin_tls, window, NULL);
+        SDL_TLSSet(_this->current_glctx_tls, ctx, NULL);
     }
-
     return retval;
 }
 
+SDL_Window *
+SDL_GL_GetCurrentWindow(void)
+{
+    if (!_this) {
+        SDL_UninitializedVideo();
+        return NULL;
+    }
+    return (SDL_Window *)SDL_TLSGet(_this->current_glwin_tls);
+}
+
+SDL_GLContext
+SDL_GL_GetCurrentContext(void)
+{
+    if (!_this) {
+        SDL_UninitializedVideo();
+        return NULL;
+    }
+    return (SDL_GLContext)SDL_TLSGet(_this->current_glctx_tls);
+}
+
 int
 SDL_GL_SetSwapInterval(int interval)
 {
     if (!_this) {
         return SDL_UninitializedVideo();
-    } else if (_this->current_glctx == NULL) {
+    } else if (SDL_GL_GetCurrentContext() == NULL) {
         return SDL_SetError("No OpenGL context has been made current");
     } else if (_this->GL_SetSwapInterval) {
         return _this->GL_SetSwapInterval(_this, interval);
@@ -2792,7 +2817,7 @@ SDL_GL_GetSwapInterval(void)
 {
     if (!_this) {
         return 0;
-    } else if (_this->current_glctx == NULL) {
+    } else if (SDL_GL_GetCurrentContext() == NULL) {
         return 0;
     } else if (_this->GL_GetSwapInterval) {
         return _this->GL_GetSwapInterval(_this);
@@ -2820,7 +2845,7 @@ SDL_GL_DeleteContext(SDL_GLContext context)
         return;
     }
 
-    if (_this->current_glctx == context) {
+    if (SDL_GL_GetCurrentContext() == context) {
         SDL_GL_MakeCurrent(NULL, NULL);
     }
 

src/video/cocoa/SDL_cocoaopengl.m

@@ -178,7 +178,7 @@
     }
 
     if (_this->gl_config.share_with_current_context) {
-        share_context = (NSOpenGLContext*)(_this->current_glctx);
+        share_context = (NSOpenGLContext*)SDL_GL_GetCurrentContext();
     }
 
     context = [[NSOpenGLContext alloc] initWithFormat:fmt shareContext:share_context];

src/video/windows/SDL_windowsopengl.c

@@ -535,7 +535,7 @@ WIN_GL_CreateContext(_THIS, SDL_Window * window)
     HGLRC context, share_context;
 
     if (_this->gl_config.share_with_current_context) {
-        share_context = (HGLRC)(_this->current_glctx);
+        share_context = (HGLRC)SDL_GL_GetCurrentContext();
     } else {
         share_context = 0;
     }

src/video/x11/SDL_x11opengl.c

@@ -532,7 +532,7 @@ X11_GL_CreateContext(_THIS, SDL_Window * window)
     GLXContext context = NULL, share_context;
 
     if (_this->gl_config.share_with_current_context) {
-        share_context = (GLXContext)(_this->current_glctx);
+        share_context = SDL_GL_GetCurrentContext();
     } else {
         share_context = NULL;
     }
@@ -683,7 +683,7 @@ X11_GL_SetSwapInterval(_THIS, int interval)
     } else if (_this->gl_data->glXSwapIntervalEXT) {
         Display *display = ((SDL_VideoData *) _this->driverdata)->display;
         const SDL_WindowData *windowdata = (SDL_WindowData *)
-            _this->current_glwin->driverdata;
+            SDL_GL_GetCurrentWindow()->driverdata;
 
         Window drawable = windowdata->xwindow;
 
@@ -727,7 +727,7 @@ X11_GL_GetSwapInterval(_THIS)
     if (_this->gl_data->glXSwapIntervalEXT) {
         Display *display = ((SDL_VideoData *) _this->driverdata)->display;
         const SDL_WindowData *windowdata = (SDL_WindowData *)
-            _this->current_glwin->driverdata;
+            SDL_GL_GetCurrentWindow()->driverdata;
         Window drawable = windowdata->xwindow;
         unsigned int allow_late_swap_tearing = 0;
         unsigned int interval = 0;