opal/context: allow the client to supply a graphics port

In Quartz, the "graphics port" bound to an NSGraphicsContext (subclassed
by OpalContext) is a CGContext. We currently initialize one in
OpalSurface if it does not exist, however we do not allow the client to
initialize a graphics context with a custom graphics port, which should
be allowed. This commit enables this feature.

Headers/opal/OpalSurface.h

@@ -35,7 +35,7 @@
   CGContextRef _x11CGContext;
 }
 
-- (id) initWithDevice: (void *)device;
+- (id) initWithDevice: (void *)device context: (CGContextRef)ctx;
 - (void *)device;
 - (CGContextRef) CGContext;
 - (NSSize) size;

Source/opal/OpalContext.m

@@ -167,8 +167,20 @@
                     : (int)y
 {
   OpalSurface *surface;
-
-  surface = [[OpalSurface alloc] initWithDevice: device];
+  
+  /*
+   * The "graphics port" associated to an OpalContext is necessarily a
+   * CGContextRef supplied by the client to back the OpalContext, instead
+   * of having us create the CGContextRef ourselves.
+   *
+   * Since -graphicsPort is overriden from NSGraphicsContext to compute the
+   * CGContextRef for an OpalSurface (which is not initialized yet), we
+   * get the _graphicsPort ivar directly to obtain the supplied CGContextRef
+   * on initialization, and use that to init our surface.
+   */
+  CGContextRef suppliedContext = self->_graphicsPort;
+  surface = [[OpalSurface alloc] initWithDevice: device
+                                        context: suppliedContext];
 
   [OGSTATE GSSetSurface: surface
                        : x

Source/opal/OpalSurface.m

@@ -70,7 +70,7 @@ static CGContextRef createCGBitmapContext(int pixelsWide,
 
 @implementation OpalSurface
 
-- (void) createCGContexts
+- (void) createCGContextsWithSuppliedBackingContext: (CGContextRef)ctx
 {
   // FIXME: this method and class presumes we are being passed
   // a window device.
@@ -83,7 +83,7 @@ static CGContextRef createCGBitmapContext(int pixelsWide,
   Display * display = _gsWindowDevice->display;
   Window window = _gsWindowDevice->ident;
 
-  _x11CGContext = OPX11ContextCreate(display, window);
+  _x11CGContext = ctx ?: OPX11ContextCreate(display, window);
 
 #if 0
   if (_gsWindowDevice->type == NSBackingStoreNonretained)
@@ -114,7 +114,9 @@ static CGContextRef createCGBitmapContext(int pixelsWide,
 
 }
 
-- (id) initWithDevice: (void *)device
+// FIXME: *VERY* bad things will happen if a non-bitmap
+// context is passed here.
+- (id) initWithDevice: (void *)device context: (CGContextRef)ctx
 {
   self = [super init];
   if (!self)
@@ -124,7 +126,7 @@ static CGContextRef createCGBitmapContext(int pixelsWide,
   // a window device.
   _gsWindowDevice = (gswindow_device_t *) device;
 
-  [self createCGContexts];
+  [self createCGContextsWithSuppliedBackingContext: ctx];
 
   return self;
 }