Fix strange behavior when dragging&dropping from MTG creative inventory

[sfence]

Add compact, short information about your PR for easier understanding:

• Goal of the PR
  Fix Strange behavior when dragging&dropping from MTG creative inventory (since #13146) #13961
• How does the PR work?
  Update inventory in case move is not allowed and update m_selected_amount
• Does it resolve any reported issue?
  Strange behavior when dragging&dropping from MTG creative inventory (since #13146) #13961
• Does this relate to a goal in the roadmap?

To do

Ready for Review.

How to test

See #13961

[sfence]

Is it safe to remove these commented lines:

void GUIFormSpecMenu::updateSelectedItem()
{
	// Don't update when dragging an item
	//if (m_selected_item && (m_selected_dragging || m_left_dragging))
	//	return;

https://github.com/sfence/minetest/blob/297434ca80ba7ea94fd9286a537c0584d4c6a69a/src/gui/guiFormSpecMenu.cpp#L3802-L3804
?

I am not able to judge if it can cause any problems in other situations.

[grorp]

I haven't (yet?) looked or tested closely, but I've already found a bug: Your changes cause crashes when using the "left-drag to distribute evenly" feature introduced by #13146.

SIGSEGV

#0  InventoryList::changeItem (this=0x0, i=2, newitem=...)
    at /mt/src/inventory.cpp:600
#1  0x000000000058d954 in GUIFormSpecMenu::OnEvent (this=0x33ff690, event=...)
    at /mt/src/gui/guiFormSpecMenu.cpp:4740
#2  0x00000000008b05e7 in irr::gui::CGUIEnvironment::postEventFromUser (this=0xebc9e0, event=...)
    at /mt/irr/src/CGUIEnvironment.cpp:533
#3  0x00000000008ada76 in irr::CIrrDeviceStub::postEventFromUser (this=0xb0cb70, event=...)
    at /mt/irr/src/CIrrDeviceStub.cpp:168
#4  0x00000000008aa088 in irr::CIrrDeviceSDL::run (this=0xb0cb70)
    at /mt/irr/src/CIrrDeviceSDL.cpp:857
#5  0x000000000047c380 in RenderingEngine::run (this=<optimized out>)
    at /mt/src/client/renderingengine.h:152
#6  Game::run (this=this@entry=0x7fffffffd018) at /mt/src/client/game.cpp:1159
#7  0x000000000048d5c5 in the_game (kill=0xac3540 <porting::g_killed>, input=0x14b8b80, rendering_engine=0xbe06e0, 
    start_data=..., error_message="", chat_backend=..., reconnect_requested=<optimized out>)
    at /mt/src/client/game.cpp:4566
#8  0x000000000043cfda in ClientLauncher::run (this=0x7fffffffd6a0, start_data=..., cmd_args=...)
    at /mt/src/client/clientlauncher.cpp:209
#9  0x00000000007dfe13 in main (argc=1, argv=0x7fffffffde68) at /mt/src/main.cpp:263

[sfence]

@grorp
Caused by the mentioned commented lines.

I use more complex condition. I do not see SIGSEG now.

[appgurueu]

(Ignore the linked PR, that was probably a typo.)

This doesn't seem to fix the issue in its current state (7d8361b): If I hold down the left mouse button (drag), there's still the strange behavior.

Screencast.from.24-05-24.23.35.02.webm

Am I missing something?

[sfence]

@appgurueu Looks like a special situation. I did not test it with one item in the inventory.

[sfence]

@appgurueu Video situation should be fixed now.

Works also with pickup and left_dragging items.

I suggest testing with all inventory features which cams with #13146.