How to use Cursor::from_callback ?

[Doublonmousse]

I was trying to reproduce https://gitlab.gnome.org/GNOME/gtk/-/blob/main/demos/gtk-demo/cursors.c?ref_type=heads but from rust to get cursors from svg files that are scaled correctly at the right size with no blurriness and I can't get it to work at all.

There was no example I could find.

Starting from the basics example, the following code

use gtk::{glib, prelude::*};

fn main() -> glib::ExitCode {
    let application = gtk::Application::builder()
        .application_id("com.github.gtk-rs.examples.basic")
        .build();
    application.connect_activate(build_ui);
    application.run()
}

fn build_ui(application: &gtk::Application) {
    let window = gtk::ApplicationWindow::new(application);

    window.set_title(Some("First GTK Program"));
    window.set_default_size(350, 70);

    let cursor_fallback = gtk::gdk::Cursor::from_callback(
        |cursor, size, scale, width, height, hotspot_x, hotspot_y| {
            *hotspot_x = (18.0*(size as f32)/32.0).round() as i32;
            *hotspot_y = (2.0*(size as f32)/32.0).round() as i32;


            let texture = gtk::gdk::Texture::from_file(&gtk::gio::File::for_path(
                "./examples/basics/test_photo.jpg",
            ))
            .expect("Texture should have been constructed");
            dbg!(&texture.width());
            dbg!(&texture.height());
            dbg!(&texture);

            *width = texture.width();
            *height = texture.height();

            dbg!(cursor);
            dbg!(size);
            dbg!(scale, &width, &height, &hotspot_x, &hotspot_y);

            texture
        },
        gtk::gdk::Cursor::from_name("default", None).as_ref(),
    );

    let button = gtk::Button::with_label("Click me!");
    button.set_cursor(cursor_fallback.as_ref());

    window.set_child(Some(&button));

    window.present();
}

(with a bogus image just to test a texture creation) segfaults with the following output

[examples/basics/main.rs:27:13] &texture.width() = 3000
[examples/basics/main.rs:28:13] &texture.height() = 2000
[examples/basics/main.rs:29:13] &texture = Texture {
    inner: TypedObjectRef {
        inner: 0x0000555555891270,
        type: GdkMemoryTexture,
    },
}
[examples/basics/main.rs:34:13] cursor = Cursor {
    inner: TypedObjectRef {
        inner: 0x00005555557fd370,
        type: GdkCursor,
    },
}
[examples/basics/main.rs:35:13] size = 24
[examples/basics/main.rs:36:13] scale = 1.0
[examples/basics/main.rs:36:13] &width = 3000
[examples/basics/main.rs:36:13] &height = 2000
[examples/basics/main.rs:36:13] &hotspot_x = 14
[examples/basics/main.rs:36:13] &hotspot_y = 2

Thread 1 "basics" received signal SIGSEGV, Segmentation fault.
0x00007ffff786a455 in gdk_texture_get_width (texture=0x555555891270) at ../gdk/gdktexture.c:813
813       g_return_val_if_fail (GDK_IS_TEXTURE (texture), 0);
(gdb) bt
#0  0x00007ffff786a455 in gdk_texture_get_width (texture=0x555555891270) at ../gdk/gdktexture.c:813
#1  0x00007ffff77cd254 in _gdk_wayland_cursor_get_buffer
    (display=0x5555556ba690 [GdkWaylandDisplay], cursor=0x5555557fd370 [GdkCursor], desired_scale=1, hotspot_x=hotspot_x@entry=0x7fffffffc5bc, hotspot_y=hotspot_y@entry=0x7fffffffc5b8, width=width@entry=0x7fffffffc5b4, height=height@entry=0x7fffffffc5b0, scale=0x7fffffffc5c0) at ../gdk/wayland/gdkcursor-wayland.c:165
#2  0x00007ffff77cd44e in gdk_wayland_device_update_surface_cursor (device=<optimized out>) at ../gdk/wayland/gdkdevice-wayland.c:380
#3  0x00007ffff7623c6a in update_cursor (toplevel=0x5555557c6830 [GtkApplicationWindow], device=<optimized out>, grab_widget=0x0, target=<optimized out>) at ../gtk/gtkwindow.c:6917
#4  gtk_window_maybe_update_cursor (window=0x5555557c6830 [GtkApplicationWindow], widget=0x0, device=0x5555556fdc70 [GdkWaylandDevice]) at ../gtk/gtkwindow.c:6960
#5  0x00007ffff75132a6 in handle_pointing_event (event=0x555555a100c0 [GdkCrossingEvent]) at ../gtk/gtkmain.c:1472
#6  gtk_main_do_event (event=0x555555a100c0 [GdkCrossingEvent]) at ../gtk/gtkmain.c:1639
#12 0x00007ffff7f655e3 in <emit signal '???' on instance 0x555555793c20 [GdkWaylandToplevel]> (instance=instance@entry=0x555555793c20, signal_id=<optimized out>, detail=detail@entry=0)
    at ../gobject/gsignal.c:3598
    #7  0x00007ffff77be528 in _gdk_marshal_BOOLEAN__POINTERv
    (closure=<optimized out>, return_value=0x7fffffffc9a0, instance=<optimized out>, args=<optimized out>, marshal_data=<optimized out>, n_params=<optimized out>, param_types=0x5555557fcbe0)
    at gdk/gdkmarshalers.c:302
    #8  0x00007ffff7867b3a in gdk_surface_event_marshallerv
    (closure=0x55555581a9c0, return_value=0x7fffffffc9a0, instance=0x555555793c20, args=0x7fffffffca80, marshal_data=0x0, n_params=1, param_types=0x5555557fcbe0) at ../gdk/gdksurface.c:465
    #9  0x00007ffff7f65412 in _g_closure_invoke_va (closure=0x55555581a9c0, return_value=0x7fffffffc9a0, instance=0x555555793c20, args=0x7fffffffca80, n_params=1, param_types=0x5555557fcbe0)
    at ../gobject/gclosure.c:980

Putting a break point on gdk_texture_get_width, we see that the adress doesn't change but the call fails when it's actually time to update the cursor

Thread 1 "basics" hit Breakpoint 1.1, gdk_texture_get_width (texture=0x55555569f910 [GdkMemoryTexture]) at ../gdk/gdktexture.c:812
812     {
(gdb) continue
Continuing.
[examples/basics/main.rs:27:13] &texture.width() = 3000
[examples/basics/main.rs:28:13] &texture.height() = 2000
[examples/basics/main.rs:29:13] &texture = Texture {
    inner: TypedObjectRef {
        inner: 0x000055555569f910,
        type: GdkMemoryTexture,
    },
}

Thread 1 "basics" hit Breakpoint 1.1, gdk_texture_get_width (texture=0x55555569f910 [GdkMemoryTexture]) at ../gdk/gdktexture.c:812
812     {
(gdb) continue
Continuing.
[examples/basics/main.rs:34:13] cursor = Cursor {
    inner: TypedObjectRef {
        inner: 0x0[Thread 0x7fffdeffd6c0 (LWP 193120) exited]
0005555557eb620,
        type: GdkCursor,
    },
}
[examples/basics/main.rs:35:13] size = 24
[examples/basics/main.rs:36:13] scale = 1.0
[examples/basics/main.rs:36:13] &width = 3000
[examples/basics/main.rs:36:13] &height = 2000
[examples/basics/main.rs:36:13] &hotspot_x = 14
[examples/basics/main.rs:36:13] &hotspot_y = 2

Thread 1 "basics" hit Breakpoint 1.1, gdk_texture_get_width (texture=0x55555569f910) at ../gdk/gdktexture.c:812
812     {
(gdb) continue
Continuing.

Thread 1 "basics" received signal SIGSEGV, Segmentation fault.
0x00007ffff786a455 in gdk_texture_get_width (texture=0x55555569f910) at ../gdk/gdktexture.c:813
813       g_return_val_if_fail (GDK_IS_TEXTURE (texture), 0);

Am I missing something ?

[Doublonmousse]

Just noticed this difference

Thread 1 "basics" hit Breakpoint 1.1, gdk_texture_get_width (texture=0x55555569f910 [GdkMemoryTexture]) at ../gdk/gdktexture.c:812
Thread 1 "basics" hit Breakpoint 1.1, gdk_texture_get_width (texture=0x55555569f910) at ../gdk/gdktexture.c:812

Notice the missing [GdkMemoryTexture] in the second line where the segfault occurs. So it's probably a cast issue (one less or one too much ?)