more robust handling of graphics buffers with very limited (e.g. netbook) graphics drivers

panda/src/wgldisplay/wglGraphicsBuffer.cxx

@@ -76,6 +76,11 @@ begin_frame(FrameMode mode, Thread *current_thread) {
   wglGraphicsStateGuardian *wglgsg;
   DCAST_INTO_R(wglgsg, _gsg, false);
 
+  HGLRC context = wglgsg->get_context(_pbuffer_dc);
+  if (context == 0) {
+    return false;
+  }
+
   if (_fb_properties.is_single_buffered()) {
     wglgsg->_wglReleaseTexImageARB(_pbuffer, WGL_FRONT_LEFT_ARB);
   } else {
@@ -87,7 +92,7 @@ begin_frame(FrameMode mode, Thread *current_thread) {
     return false;
   }
   
-  wglGraphicsPipe::wgl_make_current(_pbuffer_dc, wglgsg->get_context(_pbuffer_dc),
+  wglGraphicsPipe::wgl_make_current(_pbuffer_dc, context,
                                     &_make_current_pcollector);
   
   if (mode == FM_render) {
@@ -336,14 +341,21 @@ open_buffer() {
   HDC twindow_dc = wglgsg->get_twindow_dc();
   if (twindow_dc == 0) {
     // If we couldn't make a window, we can't get a GL context.
+    _gsg = NULL;
     return false;
   }
-  wglGraphicsPipe::wgl_make_current(twindow_dc, wglgsg->get_context(twindow_dc),
+  HGLRC context = wglgsg->get_context(twindow_dc);
+  if (context == 0) {
+    _gsg = NULL;
+    return false;
+  }
+  wglGraphicsPipe::wgl_make_current(twindow_dc, context,
                                     &_make_current_pcollector);
   wglgsg->reset_if_new();
   wglgsg->report_my_gl_errors();
   if (!wglgsg->get_fb_properties().verify_hardware_software
       (_fb_properties,wglgsg->get_gl_renderer())) {
+    _gsg = NULL;
     return false;
   }
   _fb_properties = wglgsg->get_fb_properties();
@@ -354,6 +366,7 @@ open_buffer() {
 
   if (!rebuild_bitplanes()) {
     wglGraphicsPipe::wgl_make_current(0, 0, &_make_current_pcollector);
+    _gsg = NULL;
     return false;
   }
   
@@ -519,7 +532,11 @@ rebuild_bitplanes() {
     return false;
   }
   
-  wglGraphicsPipe::wgl_make_current(twindow_dc, wglgsg->get_context(twindow_dc),
+  HGLRC context = wglgsg->get_context(twindow_dc);
+  if (context == 0) {
+    return false;
+  }
+  wglGraphicsPipe::wgl_make_current(twindow_dc, context,
                                     &_make_current_pcollector);
 
   _pbuffer = wglgsg->_wglCreatePbufferARB(twindow_dc, pfnum, 

panda/src/wgldisplay/wglGraphicsPipe.cxx

@@ -204,6 +204,12 @@ make_output(const string &name,
         ((flags&BF_require_window)!=0)) {
       return NULL;
     }
+    if ((wglgsg != 0) &&
+        (wglgsg->is_valid()) &&
+        (!wglgsg->needs_reset()) &&
+	!wglgsg->_supports_pbuffer) {
+      return NULL;
+    }
 
     if (!support_rtt) {
       if (((flags&BF_rtt_cumulative)!=0)||

panda/src/wgldisplay/wglGraphicsStateGuardian.cxx

@@ -610,6 +610,7 @@ make_context(HDC hdc) {
   if (_context == NULL) {
     wgldisplay_cat.error()
       << "Could not create GL context.\n";
+    _is_valid = false;
     return;
   }
 
@@ -627,6 +628,7 @@ make_context(HDC hdc) {
           << "Could not share texture contexts between wglGraphicsStateGuardians.\n";
         // Too bad we couldn't detect this error sooner.  Now there's
         // really no way to tell the application it's hosed.
+	_is_valid = false;
 
       } else {
         _prepared_objects = _share_with->get_prepared_objects();