Implementing an IGraphicsPort of my own [CS2 & CS3]

Question

I'm trying to implement my own graphics port so that I can draw some arbitrary page items and process the rendering methods for my own uses.<br /><br />I've implemented a GraphicsPort like this<br />>class FixupGraphicsPort : public CPMUnknown<IGraphicsPort><br /><br />which implements all methods on IGraphicsPort, and<br />>Class<br />{<br />     kFixupPathPortBoss,<br />     kOffscreenViewPortBoss,<br />     {<br />          IID_IGRAPHICSPORT, kFixupGraphicsPortImpl,     <br />     }<br />},<br /><br />I use the ViewPort I've made like this:<br />>// Make a ViewPort and an GraphicsContext that refers to it<br />InterfacePtr<IViewPort> viewPort(::CreateObject2<IViewPort>(kFixupPathPortBoss, IID_IVIEWPORT));<br />AGMGraphicsContext gc(viewPort);<br />IGraphicsContext *graphicsContext = &gc;<br />//<br />// Get the DrawMgr from the ViewPort and use it to draw. <br />InterfacePtr<IDrawMgr> drawMgr(viewPort, UseDefaultIID());<br />ASSERT(drawMgr != nil); if (!drawMgr) { break; }<br />drawMgr->Draw(graphicsContext, pageItemUID, IShape::kNoFlags);<br /><br />Unfortunately, the drawMgr->Draw() gets a null pointer exception. More specifically, the constructor for my FixupGraphicsPort gets called, and then the FixupGraphicsPort::PortDrawMgr() gets called (returns a pointer to the exact same object as the drawMgr that I did the Draw() on), then shortly after gets the null pointer exception.<br /><br />Can anyone either point out what I'm doing wrong, or suggest an alternate scheme for drawing a PageItem and processing all of the resulting IGraphicsPort method calls?<br /><br />Thanks!

Answer 1

You wouldn't by any chance be doing computer science at Cardiff university would you and have been given this as an assignment?