Set cursor on Glade-based GUI

[StefanMathis]

Hello,

this is probably a very simple problem, but I can't figure out how to set the mouse cursor type (e.g. waiting, crosshair and so on) in a GUI window created by Glade. For a non-Glade UI, I found the following issue: #516.

I tried to apply this to a Glade-based window:

# Utility function to change the mouse cursor (see https://github.com/JuliaGraphics/Gtk.jl/issues/516)
function gdk_cursor_new(id::String)
	d = ccall((:gdk_display_get_default,Gtk.libgdk),Ptr{Nothing},(Cstring,),id)
	return ccall((:gdk_cursor_new_from_name,Gtk.libgdk),Ptr{Nothing},(Ptr{Nothing}, Cstring), d, id)
end

function gdk_window_set_cursor(wnd, cursor::Ptr{Nothing})
	wptr = Gtk.GAccessor.window(wnd)
	ccall((:gdk_window_set_cursor, Gtk.libgdk), Nothing, (Ptr{Nothing}, Ptr{Nothing}), wptr, cursor)
	return Cint(false) # Return value for Gtk
end

const CURSOR_WAIT = gdk_cursor_new("wait")
const CURSOR_DEFAULT = gdk_cursor_new("default")
const CURSOR_CROSSHAIR = gdk_cursor_new("crosshair")

builder = GtkBuilder(filename="arbitraryName.glade")
win = builder["main_window"]
gdk_window_set_cursor(builder["main_window"], CURSOR_WAIT)

This leads to the following warning:

Gdk-CRITICAL **: 20:58:35.164: gdk_window_set_cursor: assertion 'GDK_IS_WINDOW (window)' failed

I found that the type of win in the example above is Gtk.GtkWindowLeaf, while the type of win in the linked thread is GtkWindowLeaf. So i suspect there is some difference here ...

If necessary, I can gladly provide a sample Glade-file to get the MWE above to run.

Thanks for your help in advance!

[tknopp]

It seems that

wptr = Gtk.GAccessor.window(wnd)

is wrong. In the linked code this was used to extract the window from the canvas. In your example you are directly passing the window. What the window function does in case you pass a window to it is unclear to me.

[StefanMathis]

When I remove this line and pass the wnd directly to the ccall, I get an error:

LoadError: MethodError: no method matching unsafe_convert(::Type{Ptr{Nothing}}, ::Gtk.GtkWindowLeaf)

If I understand correctly, this means that wnd needs to be converted to a pointer before passing it to the ccall, correct? I assume there is an GAccessor command for that (wink, wink)?

[StefanMathis]

Okay, I found an explanation here:
https://stackoverflow.com/questions/54144406/stack7229-gdk-critical-110922-221-gdk-window-get-origin-assertion-g
So the problem here is that I need to call showall(win) before ccall'ing gdk_window_set_cursor.

However, accounting for that, a new problem arised:

GLib-GObject-CRITICAL **: 14:22:12.660: g_object_ref: assertion 'G_IS_OBJECT (object)' failed

So the search continues ;-)

EDIT: This error is due to the line mentioned by @tknopp. Simply passing wnd directly in the ccall leads to silent failure, which is progress I guess ...

[tknopp]

Best would be to put a small minimal working example so that I can test this. You can also past the glade file into a string and load that string with the builder object. In that way the file is self-contained.

[StefanMathis]

Ok, I will cook up a MWE including glade later on and post it here.

[StefanMathis]

Okay, so this is a strange one ... I created the following MWE:

Glade-file (save this in a text file MWE.glade)

<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.38.2 -->
<interface>
  <requires lib="gtk+" version="3.24"/>
  <object class="GtkWindow" id="main_window">
    <property name="can-focus">False</property>
    <property name="title" translatable="yes">Simple cursor change test</property>
    <child>
      <object class="GtkBox">
        <property name="visible">True</property>
        <property name="can-focus">False</property>
        <property name="orientation">vertical</property>
        <child>
          <object class="GtkButton" id="button_waiting">
            <property name="label" translatable="yes">Click me for waiting cursor</property>
            <property name="name">button</property>
            <property name="visible">True</property>
            <property name="can-focus">True</property>
            <property name="receives-default">True</property>
          </object>
          <packing>
            <property name="expand">False</property>
            <property name="fill">True</property>
            <property name="position">0</property>
          </packing>
        </child>
        <child>
          <object class="GtkButton" id="button_default">
            <property name="label" translatable="yes">Click me for default cursor</property>
            <property name="visible">True</property>
            <property name="can-focus">True</property>
            <property name="receives-default">True</property>
          </object>
          <packing>
            <property name="expand">False</property>
            <property name="fill">True</property>
            <property name="position">1</property>
          </packing>
        </child>
        <child>
          <placeholder/>
        </child>
      </object>
    </child>
  </object>
</interface>

Julia-File:

module MWE

using Gtk
using Gtk.ShortNames

export buildGUI

# Utility function to change the mouse cursor (see https://github.com/JuliaGraphics/Gtk.jl/issues/516)
function gdk_cursor_new(id::String)
	d = ccall((:gdk_display_get_default,Gtk.libgdk),Ptr{Nothing},(Cstring,),id)
	return ccall((:gdk_cursor_new_from_name,Gtk.libgdk),Ptr{Nothing},(Ptr{Nothing}, Cstring), d, id)
end

function gdk_window_set_cursor(wnd, cursor::Ptr{Nothing})
	wptr = Gtk.GAccessor.window(wnd)
	ccall((:gdk_window_set_cursor, Gtk.libgdk), Nothing, (Ptr{Nothing}, Ptr{Nothing}), wptr, cursor)
	return Cint(false) # Return value for Gtk
end

const CURSOR_WAIT = gdk_cursor_new("wait")
const CURSOR_DEFAULT = gdk_cursor_new("default")
const CURSOR_CROSSHAIR = gdk_cursor_new("crosshair")

# ==============================================================================

# Struct for the winding GUI
mutable struct GUIContainer
    GtkBuilder::GtkBuilder
end

function buildGUI()
	filename_UI = Base.Filesystem.joinpath(@__DIR__, "MWE.glade")
	builder = GtkBuilder(filename=filename_UI)
	win = builder["main_window"]
	obj = GUIContainer(builder)

	showall(win)

	# Callback
	id = signal_connect(cb_waiting, builder["button_waiting"], "clicked", Nothing, (), false, obj)
	id = signal_connect(cb_default, builder["button_default"], "clicked", Nothing, (), false, obj)

	# Wait with programm progression until the window is closed
	c = Condition()
	signal_connect(win, :destroy) do widget
		notify(c)
	end
	@async Gtk.gtk_main()
	wait(c)
end

@guarded (nothing) function cb_waiting(widget, obj)

    gdk_window_set_cursor(obj.GtkBuilder["main_window"], CURSOR_WAIT)

    return nothing # This is important to fit with the return type
end

@guarded (nothing) function cb_default(widget, obj)

    gdk_window_set_cursor(obj.GtkBuilder["main_window"], CURSOR_DEFAULT)

    return nothing # This is important to fit with the return type
end

end # Module

using .MWE

buildGUI()

The good (or bad thing) is that this MWE works flawlessly. I tried stripping my real-world example down to the MWE, but the error persists. When I use my real-world glade file in the MWE, it works as well. So I doubt this is a problem with Gtk.jl and I think I hit a very strange corner case. So this is on me to find out. Anyway, I thought I'd leave the code for the working MWE here as documentation.

[StefanMathis]

So I found the error :-) The problem is not the builder, the problem is here:

# Utility function to change the mouse cursor (see https://github.com/JuliaGraphics/Gtk.jl/issues/516)
function gdk_cursor_new(id::String)
	d = ccall((:gdk_display_get_default,Gtk.libgdk),Ptr{Nothing},(Cstring,),id)
	return ccall((:gdk_cursor_new_from_name,Gtk.libgdk),Ptr{Nothing},(Ptr{Nothing}, Cstring), d, id)
end

function gdk_window_set_cursor(wnd, cursor::Ptr{Nothing})
	wptr = Gtk.GAccessor.window(wnd)
	ccall((:gdk_window_set_cursor, Gtk.libgdk), Nothing, (Ptr{Nothing}, Ptr{Nothing}), wptr, cursor)
	return Cint(false) # Return value for Gtk
end

const CURSOR_WAIT = gdk_cursor_new("wait")
const CURSOR_DEFAULT = gdk_cursor_new("default")
const CURSOR_CROSSHAIR = gdk_cursor_new("crosshair")

The last part where the cursor pointers are created "in advance" doesn't work in my use case because the pointer is not identified as a GObject. Anyway, the fix is simple: Create the pointer anew each time a cursor change is needed:

# Utility function to change the mouse cursor (see https://github.com/JuliaGraphics/Gtk.jl/issues/516)
function gdk_cursor_new(id::String)
	d = ccall((:gdk_display_get_default,Gtk.libgdk),Ptr{Nothing},(Cstring,),id)
	return ccall((:gdk_cursor_new_from_name,Gtk.libgdk),Ptr{Nothing},(Ptr{Nothing}, Cstring), d, id)
end

function gdk_window_set_cursor(wnd, id::String)
        cursor = gdk_cursor_new(id)
	wptr = Gtk.GAccessor.window(wnd)
	ccall((:gdk_window_set_cursor, Gtk.libgdk), Nothing, (Ptr{Nothing}, Ptr{Nothing}), wptr, cursor)
	return Cint(false) # Return value for Gtk
end

I hope this helps in case someone else stumbles upon this. As I said, this is certainly not an Gtk.jl issue, so no further action is necessary.

[tknopp]

great that you found the error. Although it is not obvious to me why curser needs to be created again and again.

[StefanMathis]

Well, to me it isn't either ;-) Especially because it works for my MWE. Perhaps I'll have a look at it again when I'm feeling bored ;-) Anyway, thank you very much for your support!