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[TF2] damage_for_force_calc in OnTakeDamage is broken #6056

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doclic opened this issue Jun 7, 2024 · 2 comments · May be fixed by ValveSoftware/source-sdk-2013#966
Open

[TF2] damage_for_force_calc in OnTakeDamage is broken #6056

doclic opened this issue Jun 7, 2024 · 2 comments · May be fixed by ValveSoftware/source-sdk-2013#966
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Team Fortress 2

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@doclic
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doclic commented Jun 7, 2024

The following vscript should, when executed, make all damage knock players back as if they took only one point of damage:

function
OnScriptHook_OnTakeDamage(params)
{
	params.damage_for_force_calc = 1.0;
}

__CollectGameEventCallbacks(this);

This however doesn't happen, damage force is still calculated normally, using params.damage.
@doclic
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doclic commented Jun 7, 2024 •
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After doing a bit of digging, it seems that in CBaseEntity::TakeDamage, damage_for_force_calc is set before calling the hook, and it's retrieved after, but the retrieved value is not used anywhere.

Edit:
I spent a bit more time on reversing, and the CTakeDamageInfo passed to CBaseEntity::OnTakeDamage has m_flDamageForForce properly set:
image
I wanted to try hooking to OnTakeDamage via a SourceMod plugin instead of a VScript, but SourceMod doesn't expose m_flDamageForForce.

While reverse-engineering, I've also found that damage_custom is effectively useless, reported in #4481.

@doclic
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doclic commented Feb 25, 2025 •
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Using the updated source-sdk-2013, I found that the problem comes from CTFGameRules::ApplyOnDamageModifyRules in game/shared/tf/tf_gamerules.cpp which starts with this line:

	info.SetDamageForForceCalc( info.GetDamage() );

which resets the damage for force calc value to the regular damage value.
Removing this line fixes the issue, and doesn't seem to break anything else. (Edit: this is wrong and I am stupid)
Only running this code if the damage for force calc is set to 0 (meaning it wasn't overridden by a mod), fixes this.

doclic added a commit to doclic/source-sdk-2013 that referenced this issue Mar 8, 2025
@doclic
tf2: Fix damage for force calc being reset
7972875 
This fixes ValveSoftware/Source-1-Games#6056
doclic added a commit to doclic/source-sdk-2013 that referenced this issue Mar 8, 2025
@doclic
tf2: Fix damage for force calc being reset
04f3b5c 
This fixes ValveSoftware/Source-1-Games#6056
doclic added a commit to doclic/source-sdk-2013 that referenced this issue Mar 8, 2025
@doclic
tf2: Allow vscript to set damage for force calc
40bcf3c 
This fixes ValveSoftware/Source-1-Games#6056
@doclic doclic linked a pull request Mar 8, 2025 that will close this issue
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[TF2] Allow vscript to set damage for force calc doclic/source-sdk-2013
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@kisak-valve @doclic