// SONIC ROBO BLAST 2
//-----------------------------------------------------------------------------
// Copyright (C) 1993-1996 by id Software, Inc.
// Copyright (C) 1998-2000 by DooM Legacy Team.
// Copyright (C) 1999-2021 by Sonic Team Junior.
//
// This program is free software distributed under the
// terms of the GNU General Public License, version 2.
// See the 'LICENSE' file for more details.
//-----------------------------------------------------------------------------
/// \file  r_plane.c
/// \brief Here is a core component: drawing the floors and ceilings,
///        while maintaining a per column clipping list only.
///        Moreover, the sky areas have to be determined.

#include <tracy/tracy/Tracy.hpp>

#include "command.h"
#include "doomdef.h"
#include "console.h"
#include "g_game.h"
#include "p_setup.h" // levelflats
#include "p_slopes.h"
#include "r_fps.h"
#include "r_data.h"
#include "r_textures.h"
#include "r_local.h"
#include "r_state.h"
#include "r_splats.h" // faB(21jan):testing
#include "r_sky.h"
#include "r_portal.h"
#include "core/thread_pool.h"

#include "v_video.h"
#include "w_wad.h"
#include "z_zone.h"
#include "p_tick.h"

extern "C" consvar_t cv_debugfinishline;

//
// opening
//

// Quincunx antialiasing of flats!
//#define QUINCUNX

//SoM: 3/23/2000: Use Boom visplane hashing.

visplane_t *visplanes[MAXVISPLANES];
static visplane_t *freetail;
static visplane_t **freehead = &freetail;

visplane_t *floorplane;
visplane_t *ceilingplane;

visffloor_t ffloor[MAXFFLOORS];
INT32 numffloors;

//SoM: 3/23/2000: Boom visplane hashing routine.
#define visplane_hash(picnum,lightlevel,height) \
  ((unsigned)((picnum)*3+(lightlevel)+(height)*7) & VISPLANEHASHMASK)

//SoM: 3/23/2000: Use boom opening limit removal
size_t maxopenings;
INT16 *openings, *lastopening; /// \todo free leak

//
// Clip values are the solid pixel bounding the range.
//  floorclip starts out SCREENHEIGHT
//  ceilingclip starts out -1
//
INT16 floorclip[MAXVIDWIDTH], ceilingclip[MAXVIDWIDTH];
fixed_t frontscale[MAXVIDWIDTH];

//
// spanstart holds the start of a plane span
// initialized to 0 at start
//
static INT32 spanstart[MAXVIDHEIGHT];

//
// texture mapping
//

//added : 10-02-98: yslopetab is what yslope used to be,
//                yslope points somewhere into yslopetab,
//                now (viewheight/2) slopes are calculated above and
//                below the original viewheight for mouselook
//                (this is to calculate yslopes only when really needed)
//                (when mouselookin', yslope is moving into yslopetab)
//                Check R_SetupFrame, R_SetViewSize for more...
fixed_t yslopetab[MAXSPLITSCREENPLAYERS][MAXVIDHEIGHT*16];
fixed_t *yslope;

//
// R_InitPlanes
// Only at game startup.
//
void R_InitPlanes(void)
{
	// FIXME: unused
}

// ripples da water texture
static fixed_t R_CalculateRippleOffset(drawspandata_t* ds, INT32 y)
{
	fixed_t distance = FixedMul(ds->planeheight, yslope[y]);
	const INT32 yay = (ds->planeripple.offset + (distance>>9)) & 8191;
	return FixedDiv(FINESINE(yay), (1<<12) + (distance>>11));
}

static void R_CalculatePlaneRipple(drawspandata_t* ds, angle_t angle)
{
	angle >>= ANGLETOFINESHIFT;
	angle = (angle + 2048) & 8191; // 90 degrees
	ds->planeripple.xfrac = FixedMul(FINECOSINE(angle), ds->bgofs);
	ds->planeripple.yfrac = FixedMul(FINESINE(angle), ds->bgofs);
}

static void R_UpdatePlaneRipple(drawspandata_t* ds)
{
	ds->waterofs = (leveltime & 1)*16384;
	ds->planeripple.offset = (leveltime * 140);
}

static void R_SetSlopePlaneVectors(drawspandata_t* ds, visplane_t *pl, INT32 y, fixed_t xoff, fixed_t yoff);

static bool R_CheckMapPlane(const char* funcname, INT32 y, INT32 x1, INT32 x2)
{
	if (x1 == x2)
		return true;

	if (x1 < x2 && x1 >= 0 && x2 < viewwidth && y >= 0 && y < viewheight)
		return true;

	CONS_Debug(DBG_RENDER, "%s: x1=%d, x2=%d at y=%d\n", funcname, x1, x2, y);
	return false;
}

static void R_MapPlane(drawspandata_t *ds, spandrawfunc_t *spanfunc, INT32 y, INT32 x1, INT32 x2, boolean allow_parallel)
{
	ZoneScoped;
	angle_t angle, planecos, planesin;
	fixed_t distance = 0, span;
	size_t pindex;

	if (!R_CheckMapPlane(__func__, y, x1, x2))
		return;

	angle = (ds->currentplane->viewangle + ds->currentplane->plangle)>>ANGLETOFINESHIFT;
	planecos = FINECOSINE(angle);
	planesin = FINESINE(angle);

	distance = FixedMul(ds->planeheight, yslope[y]);
	span = abs(centery - y);
	if (span) // Don't divide by zero
	{
		ds->xstep = FixedMul(planesin, ds->planeheight) / span;
		ds->ystep = FixedMul(planecos, ds->planeheight) / span;
	}
	else
		ds->xstep = ds->ystep = FRACUNIT;

	// [RH] Instead of using the xtoviewangle array, I calculated the fractional values
	// at the middle of the screen, then used the calculated ds_xstep and ds_ystep
	// to step from those to the proper texture coordinate to start drawing at.
	// That way, the texture coordinate is always calculated by its position
	// on the screen and not by its position relative to the edge of the visplane.
	ds->xfrac = ds->xoffs + FixedMul(planecos, distance) + (x1 - centerx) * ds->xstep;
	ds->yfrac = ds->yoffs - FixedMul(planesin, distance) + (x1 - centerx) * ds->ystep;

	// Water ripple effect
	if (ds->planeripple.active)
	{
		ds->bgofs = R_CalculateRippleOffset(ds, y);

		R_CalculatePlaneRipple(ds, ds->currentplane->viewangle + ds->currentplane->plangle);

		ds->xfrac += ds->planeripple.xfrac;
		ds->yfrac += ds->planeripple.yfrac;
		ds->bgofs >>= FRACBITS;

		if ((y + ds->bgofs) >= viewheight)
			ds->bgofs = viewheight-y-1;
		if ((y + ds->bgofs) < 0)
			ds->bgofs = -y;
	}

	if (ds->flatlighting)
	{
		ds->colormap = ds->flatlighting;
	}
	else
	{
		pindex = distance >> LIGHTZSHIFT;
		if (pindex >= MAXLIGHTZ)
			pindex = MAXLIGHTZ - 1;

		ds->colormap = ds->planezlight[pindex];

		if (!debugrender_highlight)
		{
			if (ds->currentplane->extra_colormap)
				ds->colormap = ds->currentplane->extra_colormap->colormap + (ds->colormap - colormaps);

			ds->fullbright = colormaps;
			if (encoremap && !ds->currentplane->noencore)
			{
				ds->colormap += COLORMAP_REMAPOFFSET;
				ds->fullbright += COLORMAP_REMAPOFFSET;
			}
		}
	}

	ds->y = y;
	ds->x1 = x1;
	ds->x2 = x2;

	spanfunc(ds);
}

static void R_MapTiltedPlane(drawspandata_t *ds, void(*spanfunc)(drawspandata_t*), INT32 y, INT32 x1, INT32 x2, boolean allow_parallel)
{
	ZoneScoped;

	if (!R_CheckMapPlane(__func__, y, x1, x2))
		return;

	// Water ripple effect
	if (ds->planeripple.active)
	{
		ds->bgofs = R_CalculateRippleOffset(ds, y);

		R_SetTiltedSpan(ds, std::clamp(y, 0, viewheight));

		R_CalculatePlaneRipple(ds, ds->currentplane->viewangle + ds->currentplane->plangle);
		R_SetSlopePlaneVectors(ds, ds->currentplane, y, (ds->xoffs + ds->planeripple.xfrac), (ds->yoffs + ds->planeripple.yfrac));

		ds->bgofs >>= FRACBITS;

		if ((y + ds->bgofs) >= viewheight)
			ds->bgofs = viewheight-y-1;
		if ((y + ds->bgofs) < 0)
			ds->bgofs = -y;
	}

	if (ds->currentplane->extra_colormap)
		ds->colormap = ds->currentplane->extra_colormap->colormap;
	else
		ds->colormap = colormaps;

	ds->fullbright = colormaps;
	if (encoremap && !ds->currentplane->noencore)
	{
		ds->colormap += COLORMAP_REMAPOFFSET;
		ds->fullbright += COLORMAP_REMAPOFFSET;
	}

	ds->y = y;
	ds->x1 = x1;
	ds->x2 = x2;

	spanfunc(ds);
}

void R_ClearFFloorClips (void)
{
	INT32 i, p;

	// opening / clipping determination
	for (i = 0; i < viewwidth; i++)
	{
		for (p = 0; p < MAXFFLOORS; p++)
		{
			ffloor[p].f_clip[i] = (INT16)viewheight;
			ffloor[p].c_clip[i] = -1;
		}
	}

	numffloors = 0;
}

//
// R_ClearPlanes
// At begining of frame.
//
void R_ClearPlanes(void)
{
	INT32 i, p;

	// opening / clipping determination
	for (i = 0; i < viewwidth; i++)
	{
		floorclip[i] = (INT16)viewheight;
		ceilingclip[i] = -1;
		frontscale[i] = INT32_MAX;
		for (p = 0; p < MAXFFLOORS; p++)
		{
			ffloor[p].f_clip[i] = (INT16)viewheight;
			ffloor[p].c_clip[i] = -1;
		}
	}

	for (i = 0; i < MAXVISPLANES; i++)
	for (*freehead = visplanes[i], visplanes[i] = NULL;
		freehead && *freehead ;)
	{
		freehead = &(*freehead)->next;
	}

	lastopening = openings;
}

static visplane_t *new_visplane(unsigned hash)
{
	visplane_t *check = freetail;
	if (!check)
	{
		check = static_cast<visplane_t*>(calloc(1, sizeof (*check)));
		if (check == NULL) I_Error("%s: Out of memory", "new_visplane"); // FIXME: ugly
	}
	else
	{
		freetail = freetail->next;
		if (!freetail)
			freehead = &freetail;
	}
	check->next = visplanes[hash];
	visplanes[hash] = check;

	g_renderstats.visplanes++;

	return check;
}

//
// R_FindPlane: Seek a visplane having the identical values:
//              Same height, same flattexture, same lightlevel.
//              If not, allocates another of them.
//
visplane_t *R_FindPlane(fixed_t height, INT32 picnum, INT32 lightlevel,
	fixed_t xoff, fixed_t yoff, angle_t plangle, extracolormap_t *planecolormap,
	ffloor_t *pfloor, polyobj_t *polyobj, pslope_t *slope, boolean noencore,
	boolean ripple, boolean reverseLight, const sector_t *lighting_sector,
	sectordamage_t damage)
{
	visplane_t *check;
	unsigned hash;

	if (!cv_debugfinishline.value)
	{
		damage = SD_NONE;
	}

	if (!slope) // Don't mess with this right now if a slope is involved
	{
		if (plangle != 0)
		{
			// Must use 64-bit math to avoid an overflow!
			INT64 vx = xoff + viewx;
			INT64 vy = yoff - viewy;

			// Add the view offset, rotated by the plane angle.
			float ang = ANG2RAD(plangle);
			float x = vx / (float)FRACUNIT;
			float y = vy / (float)FRACUNIT;

			vx = (x * cos(ang) + y * sin(ang)) * FRACUNIT;
			vy = (-x * sin(ang) + y * cos(ang)) * FRACUNIT;

			xoff = vx;
			yoff = vy;
		}
		else
		{
			xoff += viewx;
			yoff -= viewy;
		}
	}

	if (polyobj)
	{
		if (polyobj->angle != 0)
		{
			float ang = ANG2RAD(polyobj->angle);
			float x = FixedToFloat(polyobj->centerPt.x);
			float y = FixedToFloat(polyobj->centerPt.y);
			xoff -= FloatToFixed(x * cos(ang) + y * sin(ang));
			yoff -= FloatToFixed(x * sin(ang) - y * cos(ang));
		}
		else
		{
			xoff -= polyobj->centerPt.x;
			yoff += polyobj->centerPt.y;
		}
	}

	if (slope != NULL && P_ApplyLightOffset(lightlevel >> LIGHTSEGSHIFT, lighting_sector))
	{
		if (reverseLight && maplighting.directional == true)
		{
			lightlevel -= slope->lightOffset * 8;
		}
		else
		{
			lightlevel += slope->lightOffset * 8;
		}
	}

	// This appears to fix the Nimbus Ruins sky bug.
	if (picnum == skyflatnum && pfloor)
	{
		height = 0; // all skies map together
		lightlevel = 0;
	}

	if (!pfloor)
	{
		hash = visplane_hash(picnum, lightlevel, height);
		for (check = visplanes[hash]; check; check = check->next)
		{
			if (polyobj != check->polyobj)
				continue;
			if (height == check->height && picnum == check->picnum
				&& lightlevel == check->lightlevel
				&& xoff == check->xoffs && yoff == check->yoffs
				&& planecolormap == check->extra_colormap
				&& check->viewx == viewx && check->viewy == viewy && check->viewz == viewz
				&& check->viewangle == viewangle
				&& check->plangle == plangle
				&& check->slope == slope
				&& check->noencore == noencore
				&& check->ripple == ripple
				&& check->damage == damage)
			{
				return check;
			}
		}
	}
	else
	{
		hash = MAXVISPLANES - 1;
	}

	check = new_visplane(hash);

	check->height = height;
	check->picnum = picnum;
	check->lightlevel = lightlevel;
	check->minx = vid.width;
	check->maxx = -1;
	check->xoffs = xoff;
	check->yoffs = yoff;
	check->extra_colormap = planecolormap;
	check->ffloor = pfloor;
	check->viewx = viewx;
	check->viewy = viewy;
	check->viewz = viewz;
	check->viewangle = viewangle;
	check->plangle = plangle;
	check->polyobj = polyobj;
	check->slope = slope;
	check->noencore = noencore;
	check->ripple = ripple;
	check->damage = damage;

	memset(check->top, 0xff, sizeof (check->top));
	memset(check->bottom, 0x00, sizeof (check->bottom));

	return check;
}

//
// R_CheckPlane: return same visplane or alloc a new one if needed
//
visplane_t *R_CheckPlane(visplane_t *pl, INT32 start, INT32 stop)
{
	INT32 intrl, intrh;
	INT32 unionl, unionh;
	INT32 x;

	if (start < pl->minx)
	{
		intrl = pl->minx;
		unionl = start;
	}
	else
	{
		unionl = pl->minx;
		intrl = start;
	}

	if (stop > pl->maxx)
	{
		intrh = pl->maxx;
		unionh = stop;
	}
	else
	{
		unionh = pl->maxx;
		intrh = stop;
	}

	// 0xff is not equal to -1 with shorts...
	for (x = intrl; x <= intrh; x++)
		if (pl->top[x] != 0xffff || pl->bottom[x] != 0x0000)
			break;

	if (x > intrh) /* Can use existing plane; extend range */
	{
		pl->minx = unionl;
		pl->maxx = unionh;
	}
	else /* Cannot use existing plane; create a new one */
	{
		visplane_t *new_pl;
		if (pl->ffloor)
		{
			new_pl = new_visplane(MAXVISPLANES - 1);
		}
		else
		{
			unsigned hash =
				visplane_hash(pl->picnum, pl->lightlevel, pl->height);
			new_pl = new_visplane(hash);
		}

		new_pl->height = pl->height;
		new_pl->picnum = pl->picnum;
		new_pl->lightlevel = pl->lightlevel;
		new_pl->xoffs = pl->xoffs;
		new_pl->yoffs = pl->yoffs;
		new_pl->extra_colormap = pl->extra_colormap;
		new_pl->ffloor = pl->ffloor;
		new_pl->viewx = pl->viewx;
		new_pl->viewy = pl->viewy;
		new_pl->viewz = pl->viewz;
		new_pl->viewangle = pl->viewangle;
		new_pl->plangle = pl->plangle;
		new_pl->polyobj = pl->polyobj;
		new_pl->slope = pl->slope;
		new_pl->noencore = pl->noencore;
		new_pl->ripple = pl->ripple;
		new_pl->damage = pl->damage;
		pl = new_pl;
		pl->minx = start;
		pl->maxx = stop;
		memset(pl->top, 0xff, sizeof pl->top);
		memset(pl->bottom, 0x00, sizeof pl->bottom);
	}
	return pl;
}


//
// R_ExpandPlane
//
// This function basically expands the visplane.
// The reason for this is that when creating 3D floor planes, there is no
// need to create new ones with R_CheckPlane, because 3D floor planes
// are created by subsector and there is no way a subsector can graphically
// overlap.
void R_ExpandPlane(visplane_t *pl, INT32 start, INT32 stop)
{
	// Don't expand polyobject planes here - we do that on our own.
	if (pl->polyobj)
		return;

	if (pl->minx > start) pl->minx = start;
	if (pl->maxx < stop)  pl->maxx = stop;
}

static void R_MakeSpans(void (*mapfunc)(drawspandata_t* ds, void(*spanfunc)(drawspandata_t*), INT32, INT32, INT32, boolean), spandrawfunc_t* spanfunc, drawspandata_t* ds, INT32 x, INT32 t1, INT32 b1, INT32 t2, INT32 b2, boolean allow_parallel)
{
	ZoneScoped;
	//    Alam: from r_splats's R_RasterizeFloorSplat
	if (t1 >= vid.height) t1 = vid.height-1;
	if (b1 >= vid.height) b1 = vid.height-1;
	if (t2 >= vid.height) t2 = vid.height-1;
	if (b2 >= vid.height) b2 = vid.height-1;
	if (x-1 >= vid.width) x = vid.width;

	// We want to draw N spans per subtask to ensure the work is
	// coarse enough to not be too slow due to task scheduling overhead.
	// To safely do this, we need to copy part of spanstart to a local.
	// This is essentially loop unrolling across threads.
	constexpr const int kSpanTaskGranularity = 8;
	drawspandata_t dc_copy = *ds;
	while (t1 < t2 && t1 <= b1)
	{
		INT32 spanstartcopy[kSpanTaskGranularity] = {0};
		INT32 taskspans = 0;
		for (int i = 0; i < kSpanTaskGranularity; i++)
		{
			if (!((t1 + i) < t2 && (t1 + i) <= b1))
			{
				break;
			}
			spanstartcopy[i] = spanstart[t1 + i];
			taskspans += 1;
		}
		auto task = [=]() mutable -> void {
			for (int i = 0; i < taskspans; i++)
			{
				mapfunc(&dc_copy, spanfunc, t1 + i, spanstartcopy[i], x - 1, false);
			}
		};
		if (allow_parallel)
		{
			srb2::g_main_threadpool->schedule(std::move(task));
		}
		else
		{
			(task)();
		}
		t1 += taskspans;
	}
	while (b1 > b2 && b1 >= t1)
	{
		INT32 spanstartcopy[kSpanTaskGranularity] = {0};
		INT32 taskspans = 0;
		for (int i = 0; i < kSpanTaskGranularity; i++)
		{
			if (!((b1 - i) > b2 && (b1 - i) >= t1))
			{
				break;
			}
			spanstartcopy[i] = spanstart[b1 - i];
			taskspans += 1;
		}
		auto task = [=]() mutable -> void {
			for (int i = 0; i < taskspans; i++)
			{
				mapfunc(&dc_copy, spanfunc, b1 - i, spanstartcopy[i], x - 1, false);
			}
		};
		if (allow_parallel)
		{
			srb2::g_main_threadpool->schedule(std::move(task));
		}
		else
		{
			(task)();
		}
		b1 -= taskspans;
	}

	while (t2 < t1 && t2 <= b2)
		spanstart[t2++] = x;
	while (b2 > b1 && b2 >= t2)
		spanstart[b2--] = x;
}

void R_DrawPlanes(void)
{
	visplane_t *pl;
	INT32 i;
	drawspandata_t ds {0};

	ZoneScoped;

	R_UpdatePlaneRipple(&ds);

	for (i = 0; i < MAXVISPLANES; i++, pl++)
	{
		for (pl = visplanes[i]; pl; pl = pl->next)
		{
			if (pl->ffloor != NULL || pl->polyobj != NULL)
				continue;

			R_DrawSinglePlane(&ds, pl, cv_parallelsoftware.value);
		}
	}
}

// R_DrawSkyPlane
//
// Draws the sky within the plane's top/bottom bounds
// Note: this uses column drawers instead of span drawers, since the sky is always a texture
//
static void R_DrawSkyPlane(visplane_t *pl, void(*colfunc)(drawcolumndata_t*), boolean allow_parallel)
{
	INT32 x;
	drawcolumndata_t dc {0};

	ZoneScoped;

	R_CheckDebugHighlight(SW_HI_SKY);

	// Reset column drawer function (note: couldn't we just call walldrawerfunc directly?)
	// (that is, unless we'll need to switch drawers in future for some reason)
	R_SetColumnFunc(BASEDRAWFUNC, false);

	// use correct aspect ratio scale
	dc.iscale = skyscale[viewssnum];

	// Sky is always drawn full bright,
	//  i.e. colormaps[0] is used.
	// Because of this hack, sky is not affected
	//  by sector colormaps (INVUL inverse mapping is not implemented in SRB2 so is irrelevant).
	dc.colormap = colormaps;
	dc.fullbright = colormaps;
	if (encoremap)
	{
		dc.colormap += COLORMAP_REMAPOFFSET;
		dc.fullbright += COLORMAP_REMAPOFFSET;
	}
	dc.lightmap = colormaps;
	dc.texturemid = skytexturemid;
	dc.texheight = textureheight[skytexture]
		>>FRACBITS;
	dc.sourcelength = dc.texheight;

	x = pl->minx;

	// Precache the texture so we don't corrupt the zoned heap off-main thread
	if (!texturecache[texturetranslation[skytexture]])
	{
		R_GenerateTexture(texturetranslation[skytexture]);
	}

	while (x <= pl->maxx)
	{
		// Tune concurrency granularity here to maximize throughput
		// The cheaper colfunc is, the more coarse the task should be
		constexpr const int kSkyPlaneMacroColumns = 8;

		auto thunk = [=]() mutable -> void {
			for (int i = 0; i < kSkyPlaneMacroColumns && i + x <= pl->maxx; i++)
			{
				dc.yl = pl->top[x + i];
				dc.yh = pl->bottom[x + i];

				if (dc.yl > dc.yh)
				{
					continue;
				}

				INT32 angle = (pl->viewangle + xtoviewangle[viewssnum][x + i])>>ANGLETOSKYSHIFT;
				angle -= (skytextureoffset >> FRACBITS);

				dc.iscale = FixedMul(skyscale[viewssnum], FINECOSINE(xtoviewangle[viewssnum][x + i]>>ANGLETOFINESHIFT));
				dc.x = x + i;
				dc.source =
					R_GetColumn(texturetranslation[skytexture],
						-angle); // get negative of angle for each column to display sky correct way round! --Monster Iestyn 27/01/18
				dc.brightmap = NULL;

				colfunc(&dc);
			}
		};

		if (allow_parallel)
		{
			srb2::g_main_threadpool->schedule(std::move(thunk));
		}
		else
		{
			(thunk)();
		}

		x += kSkyPlaneMacroColumns;
	}
}

// Returns the height of the sloped plane at (x, y) as a 32.16 fixed_t
static INT64 R_GetSlopeZAt(const pslope_t *slope, fixed_t x, fixed_t y)
{
	INT64 x64 = ((INT64)x - (INT64)slope->o.x);
	INT64 y64 = ((INT64)y - (INT64)slope->o.y);

	x64 = (x64 * (INT64)slope->d.x) / FRACUNIT;
	y64 = (y64 * (INT64)slope->d.y) / FRACUNIT;

	return (INT64)slope->o.z + ((x64 + y64) * (INT64)slope->zdelta) / FRACUNIT;
}

// Sets the texture origin vector of the sloped plane.
static void R_SetSlopePlaneOrigin(drawspandata_t *ds, pslope_t *slope, fixed_t xpos, fixed_t ypos, fixed_t zpos, fixed_t xoff, fixed_t yoff, fixed_t angle)
{
	floatv3_t *p = &ds->slope_origin;

	INT64 vx = (INT64)xpos + (INT64)xoff;
	INT64 vy = (INT64)ypos - (INT64)yoff;

	float vxf = vx / (float)FRACUNIT;
	float vyf = vy / (float)FRACUNIT;
	float ang = ANG2RAD(ANGLE_270 - angle);

	// p is the texture origin in view space
	// Don't add in the offsets at this stage, because doing so can result in
	// errors if the flat is rotated.
	p->x = vxf * cos(ang) - vyf * sin(ang);
	p->z = vxf * sin(ang) + vyf * cos(ang);
	p->y = (R_GetSlopeZAt(slope, -xoff, yoff) - zpos) / (float)FRACUNIT;
}

// This function calculates all of the vectors necessary for drawing a sloped plane.
void R_SetSlopePlane(drawspandata_t* ds, pslope_t *slope, fixed_t xpos, fixed_t ypos, fixed_t zpos, fixed_t xoff, fixed_t yoff, angle_t angle, angle_t plangle)
{
	// Potentially override other stuff for now cus we're mean. :< But draw a slope plane!
	// I copied ZDoom's code and adapted it to SRB2... -Red
	floatv3_t *m = &ds->slope_v, *n = &ds->slope_u;
	fixed_t height, temp;
	float ang;

	R_SetSlopePlaneOrigin(ds, slope, xpos, ypos, zpos, xoff, yoff, angle);
	height = P_GetSlopeZAt(slope, xpos, ypos);
	ds->zeroheight = FixedToFloat(height - zpos);

	// m is the v direction vector in view space
	ang = ANG2RAD(ANGLE_180 - (angle + plangle));
	m->x = cos(ang);
	m->z = sin(ang);

	// n is the u direction vector in view space
	n->x = sin(ang);
	n->z = -cos(ang);

	plangle >>= ANGLETOFINESHIFT;
	temp = P_GetSlopeZAt(slope, xpos + FINESINE(plangle), ypos + FINECOSINE(plangle));
	m->y = FixedToFloat(temp - height);
	temp = P_GetSlopeZAt(slope, xpos + FINECOSINE(plangle), ypos - FINESINE(plangle));
	n->y = FixedToFloat(temp - height);
}

// This function calculates all of the vectors necessary for drawing a sloped and scaled plane.
void R_SetScaledSlopePlane(drawspandata_t* ds, pslope_t *slope, fixed_t xpos, fixed_t ypos, fixed_t zpos, fixed_t xs, fixed_t ys, fixed_t xoff, fixed_t yoff, angle_t angle, angle_t plangle)
{
	floatv3_t *m = &ds->slope_v, *n = &ds->slope_u;
	fixed_t height, temp;

	float xscale = FixedToFloat(xs);
	float yscale = FixedToFloat(ys);
	float ang;

	R_SetSlopePlaneOrigin(ds, slope, xpos, ypos, zpos, xoff, yoff, angle);
	height = P_GetSlopeZAt(slope, xpos, ypos);
	ds->zeroheight = FixedToFloat(height - zpos);

	// m is the v direction vector in view space
	ang = ANG2RAD(ANGLE_180 - (angle + plangle));
	m->x = yscale * cos(ang);
	m->z = yscale * sin(ang);

	// n is the u direction vector in view space
	n->x = xscale * sin(ang);
	n->z = -xscale * cos(ang);

	ang = ANG2RAD(plangle);
	temp = P_GetSlopeZAt(slope, xpos + FloatToFixed(yscale * sin(ang)), ypos + FloatToFixed(yscale * cos(ang)));
	m->y = FixedToFloat(temp - height);
	temp = P_GetSlopeZAt(slope, xpos + FloatToFixed(xscale * cos(ang)), ypos - FloatToFixed(xscale * sin(ang)));
	n->y = FixedToFloat(temp - height);
}

void R_CalculateSlopeVectors(drawspandata_t* ds)
{
	float sfmult = 65536.f;

	// Eh. I tried making this stuff fixed-point and it exploded on me. Here's a macro for the only floating-point vector function I recall using.
#define CROSS(d, v1, v2) \
d.x = (v1.y * v2.z) - (v1.z * v2.y);\
d.y = (v1.z * v2.x) - (v1.x * v2.z);\
d.z = (v1.x * v2.y) - (v1.y * v2.x)
	CROSS(ds->sup, ds->slope_origin, ds->slope_v);
	CROSS(ds->svp, ds->slope_origin, ds->slope_u);
	CROSS(ds->szp, ds->slope_v, ds->slope_u);
#undef CROSS

	ds->sup.z *= focallengthf[viewssnum];
	ds->svp.z *= focallengthf[viewssnum];
	ds->szp.z *= focallengthf[viewssnum];

	// Premultiply the texture vectors with the scale factors
	if (ds->powersoftwo)
		sfmult *= (1 << ds->nflatshiftup);

	ds->sup.x *= sfmult;
	ds->sup.y *= sfmult;
	ds->sup.z *= sfmult;
	ds->svp.x *= sfmult;
	ds->svp.y *= sfmult;
	ds->svp.z *= sfmult;
}

void R_SetTiltedSpan(drawspandata_t* ds, INT32 span)
{
	if (ds_su == NULL)
		ds_su = static_cast<floatv3_t*>(Z_Calloc(sizeof(*ds_su) * vid.height, PU_STATIC, NULL));
	if (ds_sv == NULL)
		ds_sv = static_cast<floatv3_t*>(Z_Calloc(sizeof(*ds_sv) * vid.height, PU_STATIC, NULL));
	if (ds_sz == NULL)
		ds_sz = static_cast<floatv3_t*>(Z_Calloc(sizeof(*ds_sz) * vid.height, PU_STATIC, NULL));

	ds->sup = ds_su[span];
	ds->svp = ds_sv[span];
	ds->szp = ds_sz[span];
}

static void R_SetSlopePlaneVectors(drawspandata_t* ds, visplane_t *pl, INT32 y, fixed_t xoff, fixed_t yoff)
{
	R_SetTiltedSpan(ds, y);
	R_SetSlopePlane(ds, pl->slope, pl->viewx, pl->viewy, pl->viewz, xoff, yoff, pl->viewangle, pl->plangle);
	R_CalculateSlopeVectors(ds);
}

static inline void R_AdjustSlopeCoordinates(drawspandata_t* ds, vector3_t *origin)
{
	const fixed_t modmask = ((1 << (32-ds->nflatshiftup)) - 1);

	fixed_t ox = (origin->x & modmask);
	fixed_t oy = -(origin->y & modmask);

	ds->xoffs &= modmask;
	ds->yoffs &= modmask;

	ds->xoffs -= (origin->x - ox);
	ds->yoffs += (origin->y + oy);
}

static inline void R_AdjustSlopeCoordinatesNPO2(drawspandata_t* ds, vector3_t *origin)
{
	const fixed_t modmaskw = (ds->flatwidth << FRACBITS);
	const fixed_t modmaskh = (ds->flatheight << FRACBITS);

	fixed_t ox = (origin->x % modmaskw);
	fixed_t oy = -(origin->y % modmaskh);

	ds->xoffs %= modmaskw;
	ds->yoffs %= modmaskh;

	ds->xoffs -= (origin->x - ox);
	ds->yoffs += (origin->y + oy);
}

void R_DrawSinglePlane(drawspandata_t *ds, visplane_t *pl, boolean allow_parallel)
{
	levelflat_t *levelflat;
	INT32 light = 0;
	INT32 x, stop;
	ffloor_t *rover;
	INT32 type, spanfunctype = BASEDRAWFUNC;
	debugrender_highlight_t debug = debugrender_highlight_t::SW_HI_PLANES;
	void (*mapfunc)(drawspandata_t*, void(*)(drawspandata_t*), INT32, INT32, INT32, boolean) = R_MapPlane;
	INT16 highlight = R_PlaneIsHighlighted(pl);

	if (!(pl->minx <= pl->maxx))
		return;

	ZoneScoped;

	R_UpdatePlaneRipple(ds);

	// sky flat
	if (pl->picnum == skyflatnum)
	{
		if (highlight != -1)
		{
			drawcolumndata_t dc = {};
			dc.r8_flatcolor = highlight;
			dc.lightmap = colormaps;

			for (dc.x = pl->minx; dc.x <= pl->maxx; ++dc.x)
			{
				dc.yl = pl->top[dc.x];
				dc.yh = pl->bottom[dc.x];
				R_DrawColumn_Flat(&dc);
			}
		}
		else
		{
			R_DrawSkyPlane(pl, colfunc, allow_parallel);
		}
		return;
	}

	ds->planeripple.active = false;
	ds->brightmap = NULL;
	R_SetSpanFunc(BASEDRAWFUNC, false, false);

	if (pl->polyobj)
	{
		// Hacked up support for alpha value in software mode Tails 09-24-2002 (sidenote: ported to polys 10-15-2014, there was no time travel involved -Red)
		if (pl->polyobj->translucency >= NUMTRANSMAPS)
			return; // Don't even draw it
		else if (pl->polyobj->translucency > 0)
		{
			spanfunctype = (pl->polyobj->flags & POF_SPLAT) ? SPANDRAWFUNC_TRANSSPLAT : SPANDRAWFUNC_TRANS;
			ds->transmap = R_GetTranslucencyTable(pl->polyobj->translucency);
		}
		else if (pl->polyobj->flags & POF_SPLAT) // Opaque, but allow transparent flat pixels
			spanfunctype = SPANDRAWFUNC_SPLAT;

		if (pl->polyobj->translucency == 0 || (pl->extra_colormap && (pl->extra_colormap->flags & CMF_FOG)))
			light = (pl->lightlevel >> LIGHTSEGSHIFT);
		else
			light = LIGHTLEVELS-1;
	}
	else
	{
		if (pl->ffloor)
		{
			// Don't draw planes that shouldn't be drawn.
			for (rover = pl->ffloor->target->ffloors; rover; rover = rover->next)
			{
				if ((pl->ffloor->fofflags & FOF_CUTEXTRA) && (rover->fofflags & FOF_EXTRA))
				{
					if (pl->ffloor->fofflags & FOF_EXTRA)
					{
						// The plane is from an extra 3D floor... Check the flags so
						// there are no undesired cuts.
						if (((pl->ffloor->fofflags & (FOF_FOG|FOF_SWIMMABLE)) == (rover->fofflags & (FOF_FOG|FOF_SWIMMABLE)))
							&& pl->height < *rover->topheight
							&& pl->height > *rover->bottomheight)
							return;
					}
				}
			}

			if (pl->ffloor->fofflags & FOF_TRANSLUCENT)
			{
				spanfunctype = (pl->ffloor->fofflags & FOF_SPLAT) ? SPANDRAWFUNC_TRANSSPLAT : SPANDRAWFUNC_TRANS;

				// Hacked up support for alpha value in software mode Tails 09-24-2002
				// ...unhacked by toaster 04-01-2021
				if (highlight == -1)
				{
					INT32 trans = (10*((256+12) - pl->ffloor->alpha))/255;
					if (trans >= 10)
						return; // Don't even draw it
					if (!(ds->transmap = R_GetBlendTable(pl->ffloor->blend, trans)))
						spanfunctype = SPANDRAWFUNC_SPLAT; // Opaque, but allow transparent flat pixels
				}

				if ((spanfunctype == SPANDRAWFUNC_SPLAT) || (pl->extra_colormap && (pl->extra_colormap->flags & CMF_FOG)))
					light = (pl->lightlevel >> LIGHTSEGSHIFT);
				else
					light = LIGHTLEVELS-1;
			}
			else if (pl->ffloor->fofflags & FOF_FOG)
			{
				spanfunctype = SPANDRAWFUNC_FOG;
				light = (pl->lightlevel >> LIGHTSEGSHIFT);
			}
			else light = (pl->lightlevel >> LIGHTSEGSHIFT);

			debug = SW_HI_FOFPLANES;
		}
		else
		{
			light = (pl->lightlevel >> LIGHTSEGSHIFT);

			debug = SW_HI_PLANES;
		}

#ifndef NOWATER
		if (pl->ripple)
		{
			INT32 top, bottom;

			ds->planeripple.active = true;
			if (spanfunctype == SPANDRAWFUNC_TRANS)
			{
				spanfunctype = SPANDRAWFUNC_WATER;

				// Copy the current scene, ugh
				top = pl->high-8;
				bottom = pl->low+8;

				if (top < 0)
					top = 0;
				if (bottom > viewheight)
					bottom = viewheight;

				// Only copy the part of the screen we need
				UINT8 i = R_GetViewNumber();
				INT32 scrx = 0;
				INT32 scry = top;
				INT32 offset;

				if (r_splitscreen == 1)
				{
					if (i & 1)
					{
						scry += viewheight;
					}
				}
				else
				{
					if (i & 1)
					{
						scrx += viewwidth;
					}

					if (i / 2)
					{
						scry += viewheight;
					}
				}

				offset = (scry*vid.width) + scrx;

				// No idea if this works
				VID_BlitLinearScreen(screens[0] + offset,
					screens[1] + (top*vid.width), // intentionally not +offset
					viewwidth, bottom-top,
					vid.width, vid.width);
			}
		}
#endif
	}

	ds->currentplane = pl;
	levelflat = &levelflats[pl->picnum];

	/* :james: */
	type = levelflat->type;
	switch (type)
	{
		case LEVELFLAT_NONE:
			return;
		case LEVELFLAT_FLAT:
			ds->source = (UINT8 *)R_GetFlat(levelflat->u.flat.lumpnum);
			R_CheckFlatLength(ds, W_LumpLength(levelflat->u.flat.lumpnum));
			// Raw flats always have dimensions that are powers-of-two numbers.
			ds->powersoftwo = true;
			break;
		default:
			ds->source = (UINT8 *)R_GetLevelFlat(ds, levelflat);
			if (!ds->source)
				return;
			// Check if this texture or patch has power-of-two dimensions.
			if (R_CheckPowersOfTwo(ds))
				R_CheckFlatLength(ds, ds->flatwidth * ds->flatheight);
	}

	if (type == LEVELFLAT_TEXTURE)
	{
		// Get the span's brightmap.
		// FLATS not supported, SORRY!!
		INT32 bmNum = R_GetTextureBrightmap(levelflat->u.texture.num);
		if (bmNum != 0)
		{
			// FIXME: This has the potential to read out of
			// bounds if the brightmap texture is not as
			// large as the flat.
			ds->brightmap = (UINT8 *)R_GenerateTextureAsFlat(bmNum);
		}
	}

	if (!pl->slope // Don't mess with angle on slopes! We'll handle this ourselves later
		&& viewangle != pl->viewangle+pl->plangle)
	{
		viewangle = pl->viewangle+pl->plangle;
	}

	ds->xoffs = pl->xoffs;
	ds->yoffs = pl->yoffs;

	if (light >= LIGHTLEVELS)
		light = LIGHTLEVELS-1;

	if (light < 0)
		light = 0;

	light = R_AdjustLightLevel(light);

	if (pl->slope)
	{
		mapfunc = R_MapTiltedPlane;

		if (!pl->plangle)
		{
			if (ds->powersoftwo)
				R_AdjustSlopeCoordinates(ds, &pl->slope->o);
			else
				R_AdjustSlopeCoordinatesNPO2(ds, &pl->slope->o);
		}

		if (ds->planeripple.active)
		{
			ds->planeheight = abs(P_GetSlopeZAt(pl->slope, pl->viewx, pl->viewy) - pl->viewz);

			R_PlaneBounds(pl);

			for (x = pl->high; x < pl->low; x++)
			{
				ds->bgofs = R_CalculateRippleOffset(ds, x);
				R_CalculatePlaneRipple(ds, pl->viewangle + pl->plangle);
				R_SetSlopePlaneVectors(ds, pl, x, (ds->xoffs + ds->planeripple.xfrac), (ds->yoffs + ds->planeripple.yfrac));
			}
		}
		else
			R_SetSlopePlaneVectors(ds, pl, 0, ds->xoffs, ds->yoffs);

		switch (spanfunctype)
		{
			case SPANDRAWFUNC_WATER:
				spanfunctype = SPANDRAWFUNC_TILTEDWATER;
				break;
			case SPANDRAWFUNC_TRANS:
				spanfunctype = SPANDRAWFUNC_TILTEDTRANS;
				break;
			case SPANDRAWFUNC_SPLAT:
				spanfunctype = SPANDRAWFUNC_TILTEDSPLAT;
				break;
			case SPANDRAWFUNC_TRANSSPLAT:
				spanfunctype = SPANDRAWFUNC_TILTEDTRANSSPLAT;
				break;
			case SPANDRAWFUNC_FOG:
				spanfunctype = SPANDRAWFUNC_TILTEDFOG;
				break;
			default:
				spanfunctype = SPANDRAWFUNC_TILTED;
				break;
		}

		ds->planezlight = scalelight[light];
	}
	else
	{
		ds->planeheight = abs(pl->height - pl->viewz);
		ds->planezlight = zlight[light];
	}

	if (highlight != -1 && R_SetSpanFuncFlat(BASEDRAWFUNC))
	{
		ds->r8_flatcolor = highlight;
		ds->flatlighting = colormaps;
	}
	else
	{
		R_CheckDebugHighlight(debug);

		// Use the correct span drawer depending on the powers-of-twoness
		R_SetSpanFunc(spanfunctype, !ds->powersoftwo, ds->brightmap != NULL);

		ds->flatlighting = NULL;
	}

	// set the maximum value for unsigned
	pl->top[pl->maxx+1] = 0xffff;
	pl->top[pl->minx-1] = 0xffff;
	pl->bottom[pl->maxx+1] = 0x0000;
	pl->bottom[pl->minx-1] = 0x0000;

	stop = pl->maxx + 1;

	for (x = pl->minx; x <= stop; x++)
		R_MakeSpans(mapfunc, spanfunc, ds, x, pl->top[x-1], pl->bottom[x-1], pl->top[x], pl->bottom[x], allow_parallel);
}

void R_PlaneBounds(visplane_t *plane)
{
	INT32 i;
	INT32 hi, low;

	hi = plane->top[plane->minx];
	low = plane->bottom[plane->minx];

	for (i = plane->minx + 1; i <= plane->maxx; i++)
	{
		if (plane->top[i] < hi)
		hi = plane->top[i];
		if (plane->bottom[i] > low)
		low = plane->bottom[i];
	}
	plane->high = hi;
	plane->low = low;
}

INT16 R_PlaneIsHighlighted(const visplane_t *pl)
{
	switch (pl->damage)
	{
	case SD_DEATHPIT:
	case SD_INSTAKILL:
		return 35; // red

	case SD_STUMBLE:
		return 72; // yellow

	default:
		return -1;
	}
}