Allow place_param2 values of 0 to be predicted client-side

[rollerozxa]

Minetest version

Minetest 5.8.0-rollerozxa-904d01562 (Linux)
Using Irrlicht 1.9.0mt12
Using LuaJIT 2.1.0-beta3
BUILD_TYPE=Release
RUN_IN_PLACE=0
USE_CURL=1
USE_GETTEXT=1
USE_SOUND=1
STATIC_SHAREDIR="/usr/share/minetest"
STATIC_LOCALEDIR="/usr/share/locale"

Active renderer

No response

Irrlicht device

No response

Operating system and version

Linux

CPU model

No response

GPU model

No response

OpenGL version

No response

Summary

When adding place_param2 = 0 to a node to enable the client to predict the direction of a node (e.g. planks in MTG are rotatable but should only ever be rotated at one angle when placed), it ignores the value as 0 is also used for nodes without any param2 prediction, leading to flickering textures on the client.

Steps to reproduce

1. Go into MTG, grab planks
2. Try to place them not in the direction they usually go (east or west)
3. Watch the top texture briefly flicker

[sfan5]

To no surprise this is because "0" is the neutral value so it is ignored. I wasn't totally sure if this should be a bug or feature request, now it's the latter.

[rollerozxa]

I realised I probably was a bit vague in the title so a bit of a clarification. place_param2 = 0 works on the server-side, see e.g. planks on MTG which can only placed in one direction unless rotated with a screwdriver. The issue is that the client-side can't differentiate between a value of "0" meaning "no param2 prediction, do whatever you want client" and a value of "0" meaning "set the param2 value to 0 so e.g. the node will always be at a particular angle".

[celeron55]

This goes quite deep. The network protocol requires an additional boolean value in order to enable telling the client "yes, my 0 is 0, not a command to ask you to figure out param2 on your own".

Currently 0 has a double meaning, it's only 0 if the client doesn't determine magic needs to happen based on various separate conditionals:

minetest/src/client/game.cpp

Line 3634 in 1a568cc

} else if (predicted_f.param_type_2 == CPT2_WALLMOUNTED ||

[sfan5]

place_param2 = 0 works on the server-side, see e.g. planks on MTG which can only placed in one direction

I see.
The cause for this is a bit complex: since the server placement runs in Lua which can differ between nil and 0 it works there. The C++ definition does not have that distinction. Incidentally that only makes a difference on the client, hence the mismatch you see.