BT411/game/reconstructed/dmgtable.cpp

//===========================================================================//
// File:	dmgtable.cpp                                                        //
// Project: BattleTech           Brick: Entity Manager                        //
// Contents: Damage lookup table -- layered / pie-slice hit-location selector //
//---------------------------------------------------------------------------//
//   Date    Who  Modification                                               //
// --------  ---  ---------------------------------------------------------- //
//  --/--/95  ??   Initial coding.                                            //
//  07/08/26  RE   Completed for RUNTIME (was a non-functional skeleton on    //
//                 no-op ReconTable/stream shims).  See dmgtable.hpp header.   //
//---------------------------------------------------------------------------//
// Copyright (C) 1995, Virtual World Entertainment, Inc. All Rights reserved //
//                      PROPRIETARY AND CONFIDENTIAL                         //
//===========================================================================//
//
// RECONSTRUCTED from the shipped binary.  Behaviour follows the Ghidra
// pseudo-C for the cluster @0x49de14..@0x49f5fb, cross-checked BYTE-FOR-BYTE
// against the shipped BTL4.RES type-29 resources (18 tables, exact stream
// consumption -- see context/combat-damage.md).  Each method cites its @ADDR.
//
// Float constants (read-only globals in the decomp):
//      _DAT_0049e520 = 1.0f     (percentage-sum target, offline validation)
//      _DAT_0049e72c / _DAT_0049e810 / _DAT_0049ed08 = 6.2831853f = 2*PI
//      _DAT_0049ed04 = ~1e-4f   (degenerate-direction epsilon)
//      _DAT_0049ed00 / _DAT_0049e730 = 0.0f
//
// Engine-helper name mapping:
//      FUN_00408050  RandomUnit() -> Scalar in [0,1)      (engine RandomGenerator)
//      FUN_00402948  read shared string [i32 len][len+1 bytes: chars + NUL]
//      FUN_004dc8ec  atan2f()      FUN_004dcd00 fabsf()   FUN_004dcd10/94 floorf
//      FUN_00408bf8  world->local point xform (owner+0xd0) == Mech::WorldToLocal
//

#include <bt.hpp>
#pragma hdrstop

#include <math.h>

#if !defined(DMGTABLE_HPP)
#	include <dmgtable.hpp>
#endif
#if !defined(MECH_HPP)
#	include <mech.hpp>
#endif

//
// Tuning constants observed as read-only globals in the decomp.
//
static const Scalar PercentSumTarget	= 1.0f;			// _DAT_0049e520
static const Scalar TwoPi				= 6.2831853f;	// _DAT_0049e72c / _DAT_0049e810
static const Scalar DirEpsilon			= 1.0e-4f;		// _DAT_0049ed04


//###########################################################################
//					DamageZonePercentTable          (leaf)
//###########################################################################

//
// @0x49deb0 -- stream constructor.  Stores the owner and rebuilds the entry
// list from the object stream (ReadEntries @0x49e5e4).
//
DamageZonePercentTable::DamageZonePercentTable(
	Mech			*owner,
	MemoryStream	*stream
):
	Plug(),
	owner(owner)
{
	ReadEntries(stream);
}

DamageZonePercentTable::~DamageZonePercentTable()		// @0x49df80
{
	// entries is a value vector -- frees itself.
}

//
// @0x49de14 -- the weighted random roll.  Walks the entries in ascending
// cumulative order, draws ONE uniform sample in [0,1) and returns the zone
// index of the first entry whose cumulative threshold exceeds the draw.
// -1 when the table is empty (treated as a miss by the caller).
//
int
	DamageZonePercentTable::SelectZone() const
{
	Scalar roll = RandomUnit();							// FUN_00408050
	for (unsigned i = 0; i < entries.size(); ++i)
	{
		if (roll < entries[i].cumulative)				// first threshold past the draw
		{
			return entries[i].zoneIndex;
		}
	}
	return -1;
}

//
// @0x49e5e4 -- read the leading cell NAME string (FUN_00402948: [i32 len] then
// len+1 bytes = chars + trailing NUL), then the entry count and that many
// {cumulativePercent, zoneIndex} pairs.  The name is descriptive only (the
// binary caches it but the roll never uses it), so it is consumed and dropped.
//
void
	DamageZonePercentTable::ReadEntries(MemoryStream *stream)
{
	int nameLen = 0;
	stream->ReadBytes(&nameLen, 4);						// FUN_00402948: string length
	if (nameLen > 0)
	{
		char scratch[128];
		int  total = nameLen + 1;						// chars + NUL (FUN_00402948 reads len+1)
		if (total > (int)sizeof(scratch))	total = (int)sizeof(scratch);
		stream->ReadBytes(scratch, total);				// consume name + NUL
	}

	int count = 0;
	stream->ReadBytes(&count, 4);
	entries.reserve(count > 0 ? count : 0);
	for (int i = 0; i < count; ++i)
	{
		Entry e;
		stream->ReadBytes(&e.cumulative, 4);			// f32 cumulative threshold
		stream->ReadBytes(&e.zoneIndex,  4);			// i32 zone segment index
		entries.push_back(e);
	}
}


//###########################################################################
//					PieSlice
//###########################################################################

//
// @0x49e740 -- stream constructor (vtable 0x50bd90).  Reads the RotateWithTorso
// flag (binary this[3]) and the slice count (this[0xb]) from the stream, then
// builds 'sliceCount' leaf tables.  (The torso orientation is read live via
// owner->TorsoHeading() in SelectSlice -- no cached raw pointer.)
//
PieSlice::PieSlice(
	Mech			*owner,
	MemoryStream	*stream
):
	Plug(),
	owner(owner),
	rotateWithTorso(0),
	sliceCount(0)
{
	stream->ReadBytes(&rotateWithTorso, 4);				// binary reads into this[3]
	stream->ReadBytes(&sliceCount, 4);					// this[0xb]

	slices.reserve(sliceCount > 0 ? sliceCount : 0);
	for (int i = 0; i < sliceCount; ++i)				// binary loops i=1..count building leaves
	{
		slices.push_back(new DamageZonePercentTable(owner, stream));
	}
}

PieSlice::~PieSlice()
{
	for (unsigned i = 0; i < slices.size(); ++i)
	{
		delete slices[i];
	}
}

//
// @0x49e678 -- choose the slice for incoming angle 'theta'.  When the wheel
// rotates with the torso, add the live torso twist (torso+0x1d8, via
// owner->TorsoHeading) and wrap into [0, 2*PI).  Slice index =
// floor(theta * sliceCount / 2*PI) -- direct 0-based index (equivalent to the
// binary's float-key Find((index+1)*2*PI/sliceCount)).
//
DamageZonePercentTable *
	PieSlice::SelectSlice(Scalar theta) const
{
	if (sliceCount <= 0)	return 0;

	Scalar thetaIn = theta;
	if (rotateWithTorso)								// binary this[3] != 0
	{
		// #124 frame adapter, angular half: theta arrives in the 1995 frame
		// (ResolveHit's z-reflection), so the twist -- measured in OUR frame
		// -- enters with the OPPOSITE sign (a reflection reverses angular
		// direction).  Binary form: theta += torso+0x1d8.
		theta -= owner->TorsoHeading();					// torso+0x1d8 (sign: see adapter)
		if (theta >= TwoPi)		theta -= TwoPi;
		if (theta < 0.0f)		theta += TwoPi;
	}

	int index = (int)floorf(theta * (Scalar)sliceCount * (1.0f / TwoPi));
	if (index < 0)					index = 0;
	if (index > sliceCount - 1)		index = sliceCount - 1;

	// #124 twist-sign bench: expose the twist term itself -- the leaf is a
	// weighted roll, so the SLICE choice (not the rolled zone) is the signal.
	if (getenv("BT_DMGTABLE_LOG"))
	{
		static int s_sl = 0;
		if (s_sl++ < 400)
			DEBUG_STREAM << "[slice] rot=" << (int)rotateWithTorso
				<< " twist=" << (float)owner->TorsoHeading()
				<< " thetaIn=" << (float)thetaIn
				<< " thetaAdj=" << (float)theta
				<< " -> slice " << index << "/" << sliceCount << std::endl;
	}
	return slices[index];
}


//###########################################################################
//					DamageLookupTable          (top -- layered)
//###########################################################################

//
// @0x49ea48 -- stream constructor (vtable 0x50bd84).  Reads the layer count and
// builds that many PieSlice layers from the stream.
//
DamageLookupTable::DamageLookupTable(
	Mech			*owner,
	MemoryStream	*stream
):
	Plug(),
	owner(owner),
	layerCount(0)
{
	stream->ReadBytes(&layerCount, 4);					// this[10]
	layers.reserve(layerCount > 0 ? layerCount : 0);
	for (int i = 0; i < layerCount; ++i)
	{
		layers.push_back(new PieSlice(owner, stream));
	}

	// #92 -- "unable to damage the foot panels on Loki ... could on Thor".
	// Direct-fire damage does NOT use the mesh or the aim pick: the impact's
	// HEIGHT picks a layer, its ANGLE picks a slice, and a weighted random roll
	// picks the zone from that slice.  So a zone that appears in NO slice of the
	// lowest layer is simply unreachable by direct fire.  Dump the whole table.
	if (getenv("BT_DMGTABLE_LOG"))
		DumpTable();
}

//
// #92 diagnostic: print every layer / slice / weighted zone entry.
//
void DamageLookupTable::DumpTable() const
{
	DEBUG_STREAM << "[dmgtable] layers=" << layerCount << std::endl;
	for (int L = 0; L < (int)layers.size(); ++L)
	{
		const PieSlice *layer = layers[L];
		DEBUG_STREAM << "[dmgtable]  layer " << L
			<< " rotateWithTorso=" << layer->DiagRotateWithTorso()
			<< " slices=" << layer->DiagSliceCount() << std::endl;
		for (int S = 0; S < layer->DiagSliceCount(); ++S)
		{
			const DamageZonePercentTable *leaf = layer->DiagSlice(S);
			if (leaf == 0) continue;
			DEBUG_STREAM << "[dmgtable]    slice " << S << ":";
			Scalar prev = 0.0f;
			for (int E = 0; E < leaf->DiagEntryCount(); ++E)
			{
				Scalar cum = leaf->DiagCumulative(E);
				DEBUG_STREAM << " z" << leaf->DiagZone(E)
					<< "=" << (int)((cum - prev) * 100.0f + 0.5f) << "%";
				prev = cum;
			}
			DEBUG_STREAM << std::endl;
		}
	}
}

DamageLookupTable::~DamageLookupTable()					// @0x49eadc
{
	for (unsigned i = 0; i < layers.size(); ++i)
	{
		delete layers[i];
	}
}

//
// @0x49eb54 (+ slice @0x49e678 + roll @0x49de14, chained by glue @0x49ed0c) --
// resolve a world impact point to a damage-zone index.
//   local  = owner->WorldToLocal(impact)              (owner+0xd0 xform)
//   layer  = clamp(floor(layerCount * local.y / heightRef), 0, layerCount-1)
//   theta  = atan2(local.z, local.x)  (degenerate direction -> random*2*PI)
//   zone   = layer.SelectSlice(theta).SelectZone()
// Returns -1 when the table is empty or the roll falls through (a miss).
//
int
	DamageLookupTable::ResolveHit(const Point3D &impact) const
{
	if (layerCount <= 0)	return -1;

	Point3D local     = owner->WorldToLocal(impact);			// FUN_00408bf8
	Scalar  heightRef = owner->CylinderReferenceHeight();		// owner+0x2ec[+0xc]
	if (heightRef <= 0.0f)	return -1;

	// PORT FRAME ADAPTER (#124, corrected 2026-08-03 by the MUZZLE-ANCHOR
	// probe).  The 1995 resolver frame: FORWARD = +Z (the authored ring puts
	// Front* cells in the +Z arc) and RIGHT = +X (W0/W7 = "Right*") [T1
	// slice-name data].  Our engine frame, measured with the mech's own
	// asymmetric geometry as the anchor (BT_ASPECT_TEST muzzle probes -- the
	// LEFT missile pod LRM15_1 sits at raw local x=-2.32, the RIGHT pod
	// LRM15_2 at x=+2.32): RIGHT = +X (SAME as 1995) but FORWARD = -Z
	// (drive-code convention, "forward = -Z at heading 0").  The frames
	// therefore differ by a Z-NEGATION ONLY -- a REFLECTION, not the pi
	// rotation first committed (that crossed the pods: left muzzle resolved
	// rtorso).  y (the band axis) untouched.
	//
	// A reflection reverses the angular walk direction, so the OTHER angular
	// input -- the torso-twist term SelectSlice adds -- must flip sign with
	// it (applied there, same adapter).  Twist was 0 in every probe; the
	// twisted-torso verify is the follow-up on #124.
	local.z = -local.z;

	// --- height -> layer (penetration depth) ---
	Scalar depth = local.y;										// binary local_2c
	int layerIndex = (int)floorf((Scalar)layerCount * (depth / heightRef));
	if (layerIndex < 0)					layerIndex = 0;
	if (layerIndex > layerCount - 1)	layerIndex = layerCount - 1;
	PieSlice *layer = layers[layerIndex];

	// --- in-plane hit direction -> incident angle (else random scatter) ---
	Scalar theta;
	if (fabsf(local.z) > DirEpsilon && fabsf(local.x) > DirEpsilon)
	{
		theta = atan2f(local.z, local.x);						// FUN_004dc8ec
		if (theta < 0.0f)	theta += TwoPi;
	}
	else
	{
		theta = RandomUnit() * TwoPi;							// degenerate -> uniform angle
	}

	DamageZonePercentTable *leaf = layer->SelectSlice(theta);	// FUN_0049e678
	int resolved = leaf ? leaf->SelectZone() : -1;				// FUN_0049de14

	// #92: which LAYER does a given impact height land in?  A foot shot that
	// lands in a layer above the foot layer can never roll a foot zone.
	if (getenv("BT_DMGTABLE_LOG"))
	{
		static int s_rh = 0;
		if (s_rh++ < 400)
		{
			extern int BTMechZoneSegAndName(void *mech_v, int zone_idx,
				int *seg_out, const char **name_out);
			int seg = -1; const char *zname = 0;
			if (resolved >= 0)
				BTMechZoneSegAndName((void *)owner, resolved, &seg, &zname);
			DEBUG_STREAM << "[dmgresolve] impact=(" << impact.x << ","
				<< impact.y << "," << impact.z << ")"
				<< " local=(" << local.x << "," << local.y << "," << local.z << ")"
				<< " heightRef=" << heightRef
				<< " frac=" << (depth / heightRef)
				<< " layer=" << layerIndex << "/" << layerCount
				<< " theta=" << theta
				<< " -> zone " << resolved
				<< " '" << (zname ? zname : "?") << "'" << std::endl;
		}
	}
	return resolved;
}