Semi-hack, make last known context current if NULL is current on cap

* We need a context to be current when the frame capture happens so that
  we can fetch initial contents and such. This is a hack as there's no
  guarantee it's correct or will work, but we temporarily make the last
  context that was active on this thread active again, to fetch our
  data.
* This could break if that context is active elsewhere, or isn't a valid
  context (ie. maybe it was a temporary context used to fetch func
  pointers).
* A better fix would be to delay any GL work we need to do until the
  next time a good context becomes current, but that becomes dicey in
  itself.

renderdoc/driver/gl/gl_driver.cpp

@@ -968,6 +968,9 @@ void WrappedOpenGL::CreateContext(GLWindowingData winData, void *shareContext, G
 void WrappedOpenGL::ActivateContext(GLWindowingData winData)
 {
 	m_ActiveContexts[Threading::GetCurrentID()] = winData;
+	if(winData.ctx)
+		m_DefaultContexts[Threading::GetCurrentID()] = winData;
+
 	// TODO: support multiple GL contexts more explicitly
 	Keyboard::AddInputWindow((void *)winData.wnd);
 
@@ -1895,6 +1898,15 @@ void WrappedOpenGL::Present(void *windowHandle)
 	{
 		m_State = WRITING_CAPFRAME;
 
+		GLWindowingData &prevctx = m_ActiveContexts[Threading::GetCurrentID()];
+
+		bool switchedContext = false;
+		if(prevctx.ctx == NULL)
+		{
+			MakeContextCurrent(m_DefaultContexts[Threading::GetCurrentID()]);
+			switchedContext = true;
+		}
+
 		FetchFrameRecord record;
 		record.frameInfo.frameNumber = m_FrameCounter+1;
 		record.frameInfo.captureTime = Timing::GetUnixTimestamp();
@@ -1908,6 +1920,9 @@ void WrappedOpenGL::Present(void *windowHandle)
 		AttemptCapture();
 		BeginCaptureFrame();
 
+		if(switchedContext)
+			MakeContextCurrent(prevctx);
+
 		RDCLOG("Starting capture, frame %u", m_FrameCounter);
 	}
 }

renderdoc/driver/gl/gl_driver.h

@@ -131,6 +131,10 @@ class WrappedOpenGL
 
 		map<uint64_t, GLWindowingData> m_ActiveContexts;
 
+		// we use this context if we need one e.g. for fetching initial states
+		// if no context is current
+		map<uint64_t, GLWindowingData> m_DefaultContexts;
+
 		bool m_ActiveQueries[8][8]; // first index type, second index (for some, always 0)
 		bool m_ActiveConditional;
 		bool m_ActiveFeedback;