Added the preferred widget size basework and its GTK+ implementation.

gtkcalls_unix.go

@@ -181,3 +181,11 @@ func gtk_label_set_text(widget *gtkWidget, text string) {
 func gtk_label_get_text(widget *gtkWidget) string {
 	return C.GoString(fromgchar(C.gtk_label_get_text(togtklabel(widget))))
 }
+
+func gtk_widget_get_preferred_size(w *gtkWidget) (minWidth int, minHeight int, natWidth int, natHeight int) {
+	var minimum, natural C.GtkRequisition
+
+	C.gtk_widget_get_preferred_size(togtkwidget(w), &minimum, &natural)
+	return int(minimum.width), int(minimum.height),
+		int(natural.width), int(natural.height)
+}

prefsize_unix.go

@@ -0,0 +1,21 @@
+// +build !windows,!darwin,!plan9
+
+// 23 february 2014
+package ui
+
+import (
+	// ...
+)
+
+// GTK+ 3 makes this easy: controls can tell us what their preferred size is!
+// ...actually, it tells us two things: the "minimum size" and the "natural size".
+// The "minimum size" is the smallest size we /can/ display /anything/. The "natural size" is the smallest size we would /prefer/ to display.
+// The difference? Minimum size takes into account things like truncation with ellipses: the minimum size of a label can allot just the ellipses!
+// So we use the natural size instead, right?
+// We could, but there's one snag: "Handle with care. Note that the natural height of a height-for-width widget will generally be a smaller size than the minimum height, since the required height for the natural width is generally smaller than the required height for the minimum width."
+// This will have to be taken care of manually, so TODO; we'll just use the natural size for now
+
+func (s *sysData) preferredSize() (width int, height int) {
+	_, _, width, height = gtk_widget_get_preferred_size(s.widget)
+	return width, height
+}

sysdata.go

@@ -61,6 +61,9 @@ func (c *cSysData) setWindowSize(int, int) error {
 func (c *cSysData) delete(int) error {
 	panic(runtime.GOOS + " sysData does not define delete()")
 }
+func (c *cSysData) preferredSize() (int, int) {
+	panic(runtime.GOOS + " sysData does not define preferredSize()")
+}
 
 // signal sends the event signal. This raise is done asynchronously to avoid deadlocking the UI task.
 // Thanks skelterjohn for this techinque: if we can't queue any more events, drop them