Re: getting the natural size of a widget

Julien Moutinho <[email protected]>
Newsgroups gmane.comp.lang.ocaml.lib.gtk
Message-ID <20080207155209.GA5619@localhost> 
On Wed, Feb 06, 2008 at 08:34:04PM +0000, David Powers wrote:
> I am attempting to use the GnoCanvas to build what is essentially a custom
> container.  Placing widgets on the canvas works like a charm, but I can't
> seem to find where the normal containers are reading their sizing hints
> from.  I can read the height/width_request properties, but they seem to be
> minimal sizes (e.g. for a text entry box I get a height and width of 1).
> Does anyone have any hints on where I could go hunting - or maybe I should
> be taking a different approach?

According to the following links, gtk_widget_size_request() is the way
containers read their sizing hints:

http://library.gnome.org/devel/gtk/stable/GtkContainer.html#size-requisition

  "The size requisition phase of the widget layout process operates top-down.
  It starts at a top-level widget, typically a GtkWindow.
  The top-level widget asks its child for its size requisition by calling
  gtk_widget_size_request(). To determine its requisition, the child asks
  its own children for their requisitions and so on.
  Finally, the top-level widget will get a requisition back from its child."

http://library.gnome.org/devel/gtk/stable/GtkWidget.html#gtk-widget-size-request

  "This function is typically used when implementing a GtkContainer subclass.
  Obtains the preferred size of a widget. The container uses this information
  to arrange its child widgets and decide what size allocations to give them
  with gtk_widget_size_allocate()."

Unfortunately, gtk_widget_size_request() has not been wrapped inside LablGTK yet.
However, I'm joining a little patch which wraps it plus an example that may help you.
I've also applied the patch to:
  svn://[email protected]/svn/lablgtk/branches/moutinho

NOTE: my lablgtk2 top-loop fails to run the example:
% lablgtk2 lablgtk_example__size_request.ml
Fatal error: exception Failure("float_of_string")
2%
(This bug may be related to ~x ~y ~width ~height parameters,
because without them it does not fail)

So you may have to run the example with this command:

% ocamlc -g -I +lablgtk2 lablgtk.cma lablgnomecanvas.cma gtkInit.cmo \
    lablgtk_example__size_request.ml && ./a.out
root_group#get_bounds: 0. 0. 0. 0.
widget#get_bounds: 0. 0. 23. 12.
widget#get_bounds: 25. 14. 52. 26.
List.length root_group#get_items = 2
root_group#get_bounds: 0. 0. 52. 26.
found a widget item:
  requested_width  = 23
  requested_height = 12
found a widget item:
  requested_width  = 27
  requested_height = 12

HTH.

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lablgtk_example__size_request.ml (text/plain, 2.1 KB) 
(* ocamlc -g -I +lablgtk2 lablgtk.cma lablgnomecanvas.cma gtkInit.cmo \
     lablgtk_example__size_request.ml && ./a.out *)

let window = GWindow.window () ~show: true in
let _ = window#connect#destroy ~callback: GMain.Main.quit in


let canvas = GnoCanvas.canvas ()
  ~packing: window#add in
let root_group = canvas#root in
let () =
	print_string "root_group#get_bounds:";
	Array.iter (fun x -> print_string (" "^(string_of_float x))) root_group#get_bounds;
	print_endline "" in


let widget = GMisc.label ()
  ~text: "Hello" ~show: true in
let width, height =
	GtkBase.Widget.size_request widget#as_widget in
let width  = float_of_int width
and height = float_of_int height in
let widget = GnoCanvas.widget root_group
  ~widget ~width ~height in
let () =
	print_string "widget#get_bounds:";
	Array.iter (fun x -> print_string (" "^(string_of_float x))) widget#get_bounds;
	print_endline "" in

let widget = GMisc.label ()
  ~text: "World" ~show: true in
let x, y = width +. 2., height +. 2. in
let width, height =
	GtkBase.Widget.size_request widget#as_widget in
let width  = float_of_int width
and height = float_of_int height in
let widget = GnoCanvas.widget root_group
  ~widget ~x ~y ~width ~height in
let () =
	print_string "widget#get_bounds:";
	Array.iter (fun x -> print_string (" "^(string_of_float x))) widget#get_bounds;
	print_endline "" in


print_endline ("List.length root_group#get_items = "^string_of_int (List.length root_group#get_items));
let () =
	print_string "root_group#get_bounds:";
	Array.iter (fun x -> print_string (" "^(string_of_float x))) root_group#get_bounds;
	print_endline "" in
List.iter
  begin fun item ->
	let property =
	  try Some (Gobject.Property.get_dyn item#as_item "widget")
	  with Not_found -> None in
	match property with
	| Some (`OBJECT (Some obj)) ->
		print_endline "found a widget item:";
		let obj = GtkBase.Widget.cast obj in
		let requested_width, requested_height =
		  GtkBase.Widget.size_request obj in
		print_endline ("  requested_width  = "^string_of_int requested_width);
		print_endline ("  requested_height = "^string_of_int requested_height);
	| _ -> ()
  end root_group#get_items;

GMain.Main.main ()
lablgtk__gtk_widget_size_request.patch (text/x-diff, 1.7 KB) 
Index: src/ml_gtk.c
===================================================================
--- src/ml_gtk.c	(révision 1386)
+++ src/ml_gtk.c	(copie de travail)
@@ -299,6 +299,18 @@
 ML_2 (gtk_widget_get_ancestor, GtkWidget_val, Int_val, Val_GtkWidget)
 ML_1 (gtk_widget_get_colormap, GtkWidget_val, Val_GdkColormap)
 ML_1 (gtk_widget_get_visual, GtkWidget_val, (value))
+CAMLprim value
+ml_gtk_widget_size_request (value w)
+{
+    CAMLparam1(w);
+    CAMLlocal1(ret);
+    GtkRequisition r;
+    gtk_widget_size_request (GtkWidget_val(w), &r);
+    ret = alloc_small (2,0);
+    Field(ret,0) = Val_int(r.width);
+    Field(ret,1) = Val_int(r.height);
+    CAMLreturn(ret);
+}
 CAMLprim value ml_gtk_widget_get_pointer (value w)
 {
     int x,y;
Index: src/gtkBase.ml
===================================================================
--- src/gtkBase.ml	(révision 1386)
+++ src/gtkBase.ml	(copie de travail)
@@ -64,6 +64,7 @@
   external unrealize : [>`widget] obj -> unit = "ml_gtk_widget_unrealize"
   external queue_draw : [>`widget] obj -> unit = "ml_gtk_widget_queue_draw"
   external queue_resize : [>`widget] obj -> unit = "ml_gtk_widget_queue_resize"
+  external size_request : [>`widget] obj -> Gtk.requisition = "ml_gtk_widget_size_request"
   external draw : [>`widget] obj -> Gdk.Rectangle.t option -> unit
       = "ml_gtk_widget_draw"
 (*
Index: src/gtk.ml
===================================================================
--- src/gtk.ml	(révision 1386)
+++ src/gtk.ml	(copie de travail)
@@ -135,6 +135,7 @@
 type statusbar_context
 type selection_data
 
+type requisition = int * int
 type rectangle  = { x: int; y: int; width: int; height: int }
 type target_entry = { target: string; flags: target_flags list; info: int }
 type box_packing =
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