GHOST: Fix SDL backend.

We use a hidden window for each offscreen context we need.

On X11 (linux) it does not show any other windows in the OS task bar
but it might be the case on other operating systems (untested).

intern/ghost/intern/GHOST_ContextSDL.cpp

@@ -55,6 +55,7 @@ GHOST_ContextSDL::GHOST_ContextSDL(
         int contextResetNotificationStrategy)
     : GHOST_Context(stereoVisual, numOfAASamples),
       m_window(window),
+      m_hidden_window(NULL),
       m_contextProfileMask(contextProfileMask),
       m_contextMajorVersion(contextMajorVersion),
       m_contextMinorVersion(contextMinorVersion),
@@ -62,7 +63,7 @@ GHOST_ContextSDL::GHOST_ContextSDL(
       m_contextResetNotificationStrategy(contextResetNotificationStrategy),
       m_context(NULL)
 {
-	assert(m_window  != NULL);
+	// assert(m_window  != NULL);
 }
 
 
@@ -70,7 +71,7 @@ GHOST_ContextSDL::~GHOST_ContextSDL()
 {
 	if (m_context != NULL) {
 		if (m_window != NULL && m_context == SDL_GL_GetCurrentContext())
-			SDL_GL_MakeCurrent(m_window, m_context);
+			SDL_GL_MakeCurrent(m_window, NULL);
 
 		if (m_context != s_sharedContext || s_sharedCount == 1) {
 			assert(s_sharedCount > 0);
@@ -82,6 +83,9 @@ GHOST_ContextSDL::~GHOST_ContextSDL()
 
 			SDL_GL_DeleteContext(m_context);
 		}
+
+		if (m_hidden_window != NULL)
+			SDL_DestroyWindow(m_hidden_window);
 	}
 }
 
@@ -160,6 +164,18 @@ GHOST_TSuccess GHOST_ContextSDL::initializeDrawingContext()
 		SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, m_numOfAASamples);
 	}
 
+	if (m_window == NULL) {
+		m_hidden_window = SDL_CreateWindow(
+		    "Offscreen Context Windows",
+		    SDL_WINDOWPOS_UNDEFINED,
+		    SDL_WINDOWPOS_UNDEFINED,
+		    1, 1,
+		    SDL_WINDOW_OPENGL | SDL_WINDOW_BORDERLESS | SDL_WINDOW_HIDDEN
+		);
+
+		m_window = m_hidden_window;
+	}
+
 	m_context = SDL_GL_CreateContext(m_window);
 
 	GHOST_TSuccess success;

intern/ghost/intern/GHOST_ContextSDL.h

@@ -120,6 +120,7 @@ public:
 
 private:
 	SDL_Window *m_window;
+	SDL_Window *m_hidden_window;
 
 	const int m_contextProfileMask;
 	const int m_contextMajorVersion;

intern/ghost/intern/GHOST_System.cpp

@@ -297,7 +297,9 @@ GHOST_TSuccess GHOST_System::getButtonState(GHOST_TButtonMask mask, bool& isDown
 #ifdef WITH_INPUT_NDOF
 void GHOST_System::setNDOFDeadZone(float deadzone)
 {
-	this->m_ndofManager->setDeadZone(deadzone);
+	if (this->m_ndofManager) {
+		this->m_ndofManager->setDeadZone(deadzone);
+	}
 }
 #endif
 

intern/ghost/intern/GHOST_SystemSDL.cpp

@@ -26,6 +26,7 @@
 
 #include <assert.h>
 
+#include "GHOST_ContextSDL.h"
 #include "GHOST_SystemSDL.h"
 #include "GHOST_WindowSDL.h"
 
@@ -149,6 +150,34 @@ GHOST_SystemSDL::getNumDisplays() const
 	return SDL_GetNumVideoDisplays();
 }
 
+GHOST_IContext *
+GHOST_SystemSDL::createOffscreenContext()
+{
+	GHOST_Context *context = new GHOST_ContextSDL(
+	        0,
+	        0,
+	        NULL,
+	        0, // profile bit
+	        3, 3,
+	        GHOST_OPENGL_SDL_CONTEXT_FLAGS,
+	        GHOST_OPENGL_SDL_RESET_NOTIFICATION_STRATEGY);
+
+	if (context->initializeDrawingContext())
+		return context;
+	else
+		delete context;
+
+	return NULL;
+}
+
+GHOST_TSuccess
+GHOST_SystemSDL::disposeContext(GHOST_IContext *context)
+{
+	delete context;
+
+	return GHOST_kSuccess;
+}
+
 GHOST_TSuccess
 GHOST_SystemSDL::getModifierKeys(GHOST_ModifierKeys& keys) const
 {

intern/ghost/intern/GHOST_SystemSDL.h

@@ -95,6 +95,12 @@ public:
 	getMainDisplayDimensions(GHOST_TUns32& width,
 	                         GHOST_TUns32& height) const;
 
+	GHOST_IContext *
+	createOffscreenContext();
+
+	GHOST_TSuccess
+	disposeContext(GHOST_IContext *context);
+
 	/**
 	 * Informs if the system provides native dialogs (eg. confirm quit)
 	 */

intern/ghost/intern/GHOST_WindowSDL.cpp

@@ -93,7 +93,7 @@ GHOST_WindowSDL::newDrawingContext(GHOST_TDrawingContextType type)
 		        m_wantNumOfAASamples,
 		        m_sdl_win,
 		        0, // profile bit
-		        0, 0,
+		        3, 3,
 		        GHOST_OPENGL_SDL_CONTEXT_FLAGS,
 		        GHOST_OPENGL_SDL_RESET_NOTIFICATION_STRATEGY);