Added the GTK+ implementation of Area. It's not enabled yet due to cgo bugs, and there's some extra work needed (started here) to tie this in...

area_unix.go

@@ -0,0 +1,60 @@
+// +build ignore
+// (ignored pending Go issues 7409 and 7548)
+// x+build !windows,!darwin,!plan9
+
+// 14 march 2014
+
+package ui
+
+import (
+	"image"
+)
+
+// #cgo pkg-config: gtk+-3.0
+// #include <gtk/gtk.h>
+// extern gboolean our_draw_callback(GtkWidget *, cairo_t *, gpointer);
+import "C"
+
+func gtkAreaNew() *gtkWidget {
+	drawingarea := C.gtk_drawing_area_new()
+	scrollarea := C.gtk_scrolled_window_new((*C.GtkAdjustment)(nil), (*C.GtkAdjustment)(nil))
+	// need a viewport because GtkDrawingArea isn't natively scrollable
+	C.gtk_scrolled_window_add_with_viewport(scrollarea, drawingarea)
+	return fromgtkwidget(scrollarea)
+}
+
+//export our_draw_callback
+func our_draw_callback(widget *C.GtkWidget, cr *C.cairo_t, data C.gpointer) C.gboolean {
+	var x, y, w, h C.double
+
+	s := (*sysData)(unsafe.Pointer(data))
+	// thanks to desrt in irc.gimp.net/#gtk+
+	C.cairo_clip_extents(cr, &x, &y, &w, &h)
+	cliprect := image.Rect(int(x), int(y), int(w), int(h))
+	imgret := make(chan *image.NRGBA)
+	defer close(imgret)
+	s.paint <- PaintRequest{
+		Rect:		cliprect,
+		Out:		imgret,
+	}
+	i := <-imgret
+	// pixel order is [R G B A] (see Example 1 on https://developer.gnome.org/gdk-pixbuf/2.26/gdk-pixbuf-The-GdkPixbuf-Structure.html) so we don't have to convert anything
+	// gdk-pixbuf is not alpha-premultiplied (thanks to desrt in irc.gimp.net/#gtk+)
+	pixbuf := C.gdk_pixbuf_new_from_data(
+		(*C.guchar)(unsafe.Pointer(&i.Pix[0])),
+		C.GDK_COLORSPACE_RGB,
+		C.TRUE,			// has alpha channel
+		8,				// bits per sample
+		C.int(i.Rect.Dx()),
+		C.int(i.Rect.Dy()),
+		C.int(i.Stride),
+		nil, nil)			// do not free data
+	C.gdk_cairo_set_source_pixbuf(cr,
+		pixbuf,
+		C.gdouble(cliprect.Min.X),
+		C.gdouble(cliprect.Min.Y))
+	C.g_object_unref((C.gpointer)(unsafe.Pointer(pixbuf)))		// free pixbuf
+	return C.FALSE		// TODO what does this return value mean? docs don't say
+}
+
+var draw_callback = C.GCallback(C.our_draw_callback)