NPAPI plugin develop on mac10.8

I have some problems，i use xcode write a npapi plugin on mac10.8,I want to draw a picture on the plugin but when i get the pNPWindow->window pointer through NPP_SetWindow(NPP instance, NPWindow* pNPWindow); I find that nNPWindow－>window is NULL ,i spend must to find the problem，but i can not，somebody can help me。 sorry，my english so poor。

code is like that,

    NPError NPP_New(NPMIMEType pluginType, NPP instance, uint16_t mode, int16_t argc, char*     argn[], char* argv[], NPSavedData* saved)
    {
        if(instance == NULL)
            return NPERR_INVALID_INSTANCE_ERROR;

        CPlugin *plugin = new CPlugin(instance);
        if(plugin == NULL)
            return NPERR_OUT_OF_MEMORY_ERROR;
        instance->pdata = (void *)plugin;

        NPBool supportsCG = false;
        NPError err;
        err = browser->getvalue(instance, NPNVsupportsCoreGraphicsBool,&supportsCG);

        if (err == NPERR_NO_ERROR && supportsCG)
             browser->setvalue(instance,NPPVpluginDrawingModel,(void*)NPDrawingModelCoreGraphics);

        return NPERR_NO_ERROR;
    }

    NPError NPP_SetWindow(NPP instance, NPWindow* pNPWindow)
   { 
        if(instance == NULL)
            return NPERR_INVALID_INSTANCE_ERROR;
        if(pNPWindow == NULL)
            return NPERR_GENERIC_ERROR;

        if(pNPWindow->window)
            writelog("window != NULL");

        if(pNPWindow->window == NULL)  ／／this is he problem pNPWindow->window always NULL
            writelog("window == NULL");

        return NPERR_NO_ERROR;
    }

Solution

Anything you're going to use on Mac 10.8 won't support the carbon event model, so window will always be NULL. Assuming that you're trying to use the CoreGraphics drawing model you will get the CGContextRef when the event is fired to draw.

See https://wiki.mozilla.org/NPAPI:CocoaEventModel for more information on the Cocoa event model. The other option you have is the CoreAnimation model (with the InvalidatingCoreAnimation model on firefox and chrome)

You might want to take a look at FireBreath, which works on 10.8 and abstracts all of the complication of this stuff for you.