Allow GpGraphics to take ownership of GpMetafile on dispose

The Windows GDI+ allows the metafile instance to be disposed before the
graphics instance.

To support that, keep track in the GpGraphics of whether it is responsible for
freeing the GpMetafile.

If the graphics instance is deleted first, own_metafile is FALSE and nothing
happens.

If the metafile instance is disposed first, set own_metafile to TRUE and don't
dispose of the metafile. It will be disposed when the graphics instance is
deleted.

---

Also on Windows GDI+ creating more than one graphics instance for a metafile
instance throws an OutOfMemoryException, so do the same in GdipGetImageGraphicsContext

src/graphics-private.h

@@ -126,6 +126,7 @@ typedef struct _Graphics {
 	float			aa_offset_y;
 	/* metafile-specific stuff */
 	EmfType			emf_type;
+	BOOL			own_metafile;	/* true when metafile is owned by the graphics instance */
 	GpMetafile		*metafile;
 	cairo_surface_t		*metasurface;	/* bogus surface to satisfy some API calls */
 	/* common-stuff */

src/graphics.c

@@ -201,6 +201,11 @@ gdip_graphics_metafile_init (GpGraphics *graphics, GpMetafile *metafile)
 	graphics->metasurface = cairo_image_surface_create (CAIRO_FORMAT_A1, 1, 1);
 	graphics->ct = cairo_create (graphics->metasurface);
 	graphics->metafile = metafile;
+	graphics->own_metafile = FALSE;
+
+	g_assert (metafile->graphics == NULL);
+	/* Track the graphics instance in the metafile */
+	metafile->graphics = graphics;
 
 	gdip_graphics_common_init (graphics);
 }
@@ -455,8 +460,15 @@ GdipDeleteGraphics (GpGraphics *graphics)
 
 	if (graphics->backend == GraphicsBackEndMetafile) {
 		/* if recording this is where we save the metafile (stream or file) */
-		if (graphics->metafile->recording)
+		if (graphics->metafile && graphics->metafile->recording)
 			gdip_metafile_stop_recording (graphics->metafile);
+		/* break the link to the metafile */
+		if (graphics->metafile)
+			graphics->metafile->graphics = NULL;
+		if (graphics->own_metafile)
+			gdip_metafile_dispose (graphics->metafile);
+		graphics->metafile = NULL;
+		graphics->own_metafile = FALSE;
 		cairo_surface_destroy (graphics->metasurface);
 		graphics->metasurface = NULL;
 	}

src/image.c

@@ -295,6 +295,9 @@ GdipGetImageGraphicsContext (GpImage *image, GpGraphics **graphics)
 		GpMetafile *mf = (GpMetafile*)image;
 		if (!mf->recording)
 			return OutOfMemory;
+		/* creating more than one graphics instance for a metafile is not supported */
+		if (mf->graphics)
+			return OutOfMemory;
 		*graphics = gdip_metafile_graphics_new (mf);
 		return *graphics ? Ok : OutOfMemory;
 	}

src/metafile-private.h

@@ -68,6 +68,7 @@ struct _Metafile {
 	BOOL recording;		/* recording into memory (data), file (fp) or user stream (stream) */
 	FILE *fp;
 	void *stream;
+	GpGraphics *graphics;	/* set if GdipGetImageGraphicsContext was called */
 };
 
 typedef struct {

src/metafile.c

@@ -918,6 +918,7 @@ gdip_metafile_create ()
 		mf->recording = FALSE;
 		mf->fp = NULL;
 		mf->stream = NULL;
+		mf->graphics = NULL;
 	}
 	return mf;
 }
@@ -970,6 +971,13 @@ gdip_metafile_dispose (GpMetafile *metafile)
 	if (!metafile)
 		return InvalidParameter;
 
+	if (metafile->graphics) {
+		g_assert (!metafile->graphics->own_metafile);
+		g_assert (metafile->graphics->metafile == metafile);
+		/* Transfer responsiblity to the graphics instance that outlives this metafile instance */
+		metafile->graphics->own_metafile = TRUE;
+		return Ok;
+	}
 	/* TODO deal with "delete" flag */
 	metafile->length = 0;
 	if (metafile->data) {
@@ -980,6 +988,9 @@ gdip_metafile_dispose (GpMetafile *metafile)
 	if (metafile->recording)
 		gdip_metafile_stop_recording (metafile);
 
+	/* if there was a graphics instance, it should already be cleaned up */
+	g_assert (metafile->graphics == NULL);
+
 	GdipFree (metafile);
 	return Ok;
 }