Fixed the problems associated with hiding and displaying the spike canvas. Hiding and then reshowing the canvas caused a new openGL context be be created. This invalidated the handles to the previous Textures and FrameBufferObjects making it impossible to render to them. Each ProjectionPlot::plot() call now checks for openGL errors, if any occur then the Texture is invalidated and a new Texture and FrameBufferObject is created for rendering.  Additionally, in order for 'historical' spikes to show up after the texture is recreated I actually have to render the texture twice. I'm not sure what bug is causing this behavior.