text: /*
  Copyright (C) 1996-1997 Id Software, Inc.
  
  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation; either version 2
  of the License, or (at your option) any later version.
  
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
  
  See the GNU General Public License for more details.
  
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  
  */
  // r_edge.c
  
  #include "quakedef.h"
  #include "r_local.h"
  
  #if 0
  // FIXME
  the complex cases add new polys on most lines, so dont optimize for keeping them the same
  have multiple free span lists to try to get better coherence?
  low depth complexity -- 1 to 3 or so
  
  this breaks spans at every edge, even hidden ones (bad)
  
  have a sentinal at both ends?
  #endif
  
  
  edge_t	*auxedges;
  edge_t	*r_edges, *edge_p, *edge_max;
  
  surf_t	*surfaces, *surface_p, *surf_max;
  
  // surfaces are generated in back to front order by the bsp, so if a surf
  // pointer is greater than another one, it should be drawn in front
  // surfaces[1] is the background, and is used as the active surface stack
  
  edge_t	*newedges[MAXHEIGHT];
  edge_t	*removeedges[MAXHEIGHT];
  
  espan_t	*span_p, *max_span_p;
  
  int		r_currentkey;
  
  extern	int	screenwidth;
  
  int	current_iv;
  
  int	edge_head_u_shift20, edge_tail_u_shift20;
  
  static void (*pdrawfunc)(void);
  
  edge_t	edge_head;
  edge_t	edge_tail;
  edge_t	edge_aftertail;
  edge_t	edge_sentinel;
  
  float	fv;
  
  void R_GenerateSpans (void);
  void R_GenerateSpansBackward (void);
  
  void R_LeadingEdge (edge_t *edge);
  void R_LeadingEdgeBackwards (edge_t *edge);
  void R_TrailingEdge (surf_t *surf, edge_t *edge);
  
  
  //=============================================================================
  
  
  /*
  ==============
  R_DrawCulledPolys
  ==============
  */
  void R_DrawCulledPolys (void)
  {
  	surf_t			*s;
  	msurface_t		*pface;
  
  	currententity = &r_worldentity;
  
  	if (r_worldpolysbacktofront)
  	{
  		for (s=surface_p-1 ; s>&surfaces[1] ; s--)
  		{
  			if (!s->spans)
  				continue;
  
  			if (!(s->flags & SURF_DRAWBACKGROUND))
  			{
  				pface = (msurface_t *)s->data;
  				R_RenderPoly (pface, 15);
  			}
  		}
  	}
  	else
  	{
  		for (s = &surfaces[1] ; s<surface_p ; s++)
  		{
  			if (!s->spans)
  				continue;
  
  			if (!(s->flags & SURF_DRAWBACKGROUND))
  			{
  				pface = (msurface_t *)s->data;
  				R_RenderPoly (pface, 15);
  			}
  		}
  	}
  }
  
  
  /*
  ==============
  R_BeginEdgeFrame
  ==============
  */
  void R_BeginEdgeFrame (void)
  {
  	int		v;
  
  	edge_p = r_edges;
  	edge_max = &r_edges[r_numallocatededges];
  
  	surface_p = &surfaces[2];	// background is surface 1,
  								//  surface 0 is a dummy
  	surfaces[1].spans = NULL;	// no background spans yet
  	surfaces[1].flags = SURF_DRAWBACKGROUND;
  
  // put the background behind everything in the world
  	if (r_draworder.value)
  	{
  		pdrawfunc = R_GenerateSpansBackward;
  		surfaces[1].key = 0;
  		r_currentkey = 1;
  	}
  	else
  	{
  		pdrawfunc = R_GenerateSpans;
  		surfaces[1].key = 0x7FFFFFFF;
  		r_currentkey = 0;
  	}
  
  // FIXME: set with memset
  	for (v=r_refdef.vrect.y ; v<r_refdef.vrectbottom ; v++)
  	{
  		newedges[v] = removeedges[v] = NULL;
  	}
  }
  
  
  #if	!id386
  
  /*
  ==============
  R_InsertNewEdges
  
  Adds the edges in the linked list edgestoadd, adding them to the edges in the
  linked list edgelist.  edgestoadd is assumed to be sorted on u, and non-empty (this is actually newedges[v]).  edgelist is assumed to be sorted on u, with a
  sentinel at the end (actually, this is the active edge table starting at
  edge_head.next).
  ==============
  */
  void R_InsertNewEdges (edge_t *edgestoadd, edge_t *edgelist)
  {
  	edge_t	*next_edge;
  
  	do
  	{
  		next_edge = edgestoadd->next;
  edgesearch:
  		if (edgelist->u >= edgestoadd->u)
  			goto addedge;
  		edgelist=edgelist->next;
  		if (edgelist->u >= edgestoadd->u)
  			goto addedge;
  		edgelist=edgelist->next;
  		if (edgelist->u >= edgestoadd->u)
  			goto addedge;
  		edgelist=edgelist->next;
  		if (edgelist->u >= edgestoadd->u)
  			goto addedge;
  		edgelist=edgelist->next;
  		goto edgesearch;
  
  	// insert edgestoadd before edgelist
  addedge:
  		edgestoadd->next = edgelist;
  		edgestoadd->prev = edgelist->prev;
  		edgelist->prev->next = edgestoadd;
  		edgelist->prev = edgestoadd;
  	} while ((edgestoadd = next_edge) != NULL);
  }
  
  #endif	// !id386
  	
  
  #if	!id386
  
  /*
  ==============
  R_RemoveEdges
  ==============
  */
  void R_RemoveEdges (edge_t *pedge)
  {
  
  	do
  	{
  		pedge->next->prev = pedge->prev;
  		pedge->prev->next = pedge->next;
  	} while ((pedge = pedge->nextremove) != NULL);
  }
  
  #endif	// !id386
  
  
  #if	!id386
  
  /*
  ==============
  R_StepActiveU
  ==============
  */
  void R_StepActiveU (edge_t *pedge)
  {
  	edge_t		*pnext_edge, *pwedge;
  
  	while (1)
  	{
  nextedge:
  		pedge->u += pedge->u_step;
  		if (pedge->u < pedge->prev->u)
  			goto pushback;
  		pedge = pedge->next;
  			
  		pedge->u += pedge->u_step;
  		if (pedge->u < pedge->prev->u)
  			goto pushback;
  		pedge = pedge->next;
  			
  		pedge->u += pedge->u_step;
  		if (pedge->u < pedge->prev->u)
  			goto pushback;
  		pedge = pedge->next;
  			
  		pedge->u += pedge->u_step;
  		if (pedge->u < pedge->prev->u)
  			goto pushback;
  		pedge = pedge->next;
  			
  		goto nextedge;		
  		
  pushback:
  		if (pedge == &edge_aftertail)
  			return;
  			
  	// push it back to keep it sorted		
  		pnext_edge = pedge->next;
  
  	// pull the edge out of the edge list
  		pedge->next->prev = pedge->prev;
  		pedge->prev->next = pedge->next;
  
  	// find out where the edge goes in the edge list
  		pwedge = pedge->prev->prev;
  
  		while (pwedge->u > pedge->u)
  		{
  			pwedge = pwedge->prev;
  		}
  
  	// put the edge back into the edge list
  		pedge->next = pwedge->next;
  		pedge->prev = pwedge;
  		pedge->next->prev = pedge;
  		pwedge->next = pedge;
  
  		pedge = pnext_edge;
  		if (pedge == &edge_tail)
  			return;
  	}
  }
  
  #endif	// !id386
  
  
  /*
  ==============
  R_CleanupSpan
  ==============
  */
  void R_CleanupSpan ()
  {
  	surf_t	*surf;
  	int		iu;
  	espan_t	*span;
  
  // now that we've reached the right edge of the screen, we're done with any
  // unfinished surfaces, so emit a span for whatever's on top
  	surf = surfaces[1].next;
  	iu = edge_tail_u_shift20;
  	if (iu > surf->last_u)
  	{
  		span = span_p++;
  		span->u = surf->last_u;
  		span->count = iu - span->u;
  		span->v = current_iv;
  		span->pnext = surf->spans;
  		surf->spans = span;
  	}
  
  // reset spanstate for all surfaces in the surface stack
  	do
  	{
  		surf->spanstate = 0;
  		surf = surf->next;
  	} while (surf != &surfaces[1]);
  }
  
  
  /*
  ==============
  R_LeadingEdgeBackwards
  ==============
  */
  void R_LeadingEdgeBackwards (edge_t *edge)
  {
  	espan_t			*span;
  	surf_t			*surf, *surf2;
  	int				iu;
  
  // it's adding a new surface in, so find the correct place
  	surf = &surfaces[edge->surfs[1]];
  
  // don't start a span if this is an inverted span, with the end
  // edge preceding the start edge (that is, we've already seen the
  // end edge)
  	if (++surf->spanstate == 1)
  	{
  		surf2 = surfaces[1].next;
  
  		if (surf->key > surf2->key)
  			goto newtop;
  
  	// if it's two surfaces on the same plane, the one that's already
  	// active is in front, so keep going unless it's a bmodel
  		if (surf->insubmodel && (surf->key == surf2->key))
  		{
  		// must be two bmodels in the same leaf; don't care, because they'll
  		// never be farthest anyway
  			goto newtop;
  		}
  
  continue_search:
  
  		do
  		{
  			surf2 = surf2->next;
  		} while (surf->key < surf2->key);
  
  		if (surf->key == surf2->key)
  		{
  		// if it's two surfaces on the same plane, the one that's already
  		// active is in front, so keep going unless it's a bmodel
  			if (!surf->insubmodel)
  				goto continue_search;
  
  		// must be two bmodels in the same leaf; don't care which is really
  		// in front, because they'll never be farthest anyway
  		}
  
  		goto gotposition;
  
  newtop:
  	// emit a span (obscures current top)
  		iu = edge->u >> 20;
  
  		if (iu > surf2->last_u)
  		{
  			span = span_p++;
  			span->u = surf2->last_u;
  			span->count = iu - span->u;
  			span->v = current_iv;
  			span->pnext = surf2->spans;
  			surf2->spans = span;
  		}
  
  		// set last_u on the new span
  		surf->last_u = iu;
  				
  gotposition:
  	// insert before surf2
  		surf->next = surf2;
  		surf->prev = surf2->prev;
  		surf2->prev->next = surf;
  		surf2->prev = surf;
  	}
  }
  
  
  /*
  ==============
  R_TrailingEdge
  ==============
  */
  void R_TrailingEdge (surf_t *surf, edge_t *edge)
  {
  	espan_t			*span;
  	int				iu;
  
  // don't generate a span if this is an inverted span, with the end
  // edge preceding the start edge (that is, we haven't seen the
  // start edge yet)
  	if (--surf->spanstate == 0)
  	{
  		if (surf->insubmodel)
  			r_bmodelactive--;
  
  		if (surf == surfaces[1].next)
  		{
  		// emit a span (current top going away)
  			iu = edge->u >> 20;
  			if (iu > surf->last_u)
  			{
  				span = span_p++;
  				span->u = surf->last_u;
  				span->count = iu - span->u;
  				span->v = current_iv;
  				span->pnext = surf->spans;
  				surf->spans = span;
  			}
  
  		// set last_u on the surface below
  			surf->next->last_u = iu;
  		}
  
  		surf->prev->next = surf->next;
  		surf->next->prev = surf->prev;
  	}
  }
  
  
  #if	!id386
  
  /*
  ==============
  R_LeadingEdge
  ==============
  */
  void R_LeadingEdge (edge_t *edge)
  {
  	espan_t			*span;
  	surf_t			*surf, *surf2;
  	int				iu;
  	double			fu, newzi, testzi, newzitop, newzibottom;
  
  	if (edge->surfs[1])
  	{
  	// it's adding a new surface in, so find the correct place
  		surf = &surfaces[edge->surfs[1]];
  
  	// don't start a span if this is an inverted span, with the end
  	// edge preceding the start edge (that is, we've already seen the
  	// end edge)
  		if (++surf->spanstate == 1)
  		{
  			if (surf->insubmodel)
  				r_bmodelactive++;
  
  			surf2 = surfaces[1].next;
  
  			if (surf->key < surf2->key)
  				goto newtop;
  
  		// if it's two surfaces on the same plane, the one that's already
  		// active is in front, so keep going unless it's a bmodel
  			if (surf->insubmodel && (surf->key == surf2->key))
  			{
  			// must be two bmodels in the same leaf; sort on 1/z
  				fu = (float)(edge->u - 0xFFFFF) * (1.0 / 0x100000);
  				newzi = surf->d_ziorigin + fv*surf->d_zistepv +
  						fu*surf->d_zistepu;
  				newzibottom = newzi * 0.99;
  
  				testzi = surf2->d_ziorigin + fv*surf2->d_zistepv +
  						fu*surf2->d_zistepu;
  
  				if (newzibottom >= testzi)
  				{
  					goto newtop;
  				}
  
  				newzitop = newzi * 1.01;
  				if (newzitop >= testzi)
  				{
  					if (surf->d_zistepu >= surf2->d_zistepu)
  					{
  						goto newtop;
  					}
  				}
  			}
  
  continue_search:
  
  			do
  			{
  				surf2 = surf2->next;
  			} while (surf->key > surf2->key);
  
  			if (surf->key == surf2->key)
  			{
  			// if it's two surfaces on the same plane, the one that's already
  			// active is in front, so keep going unless it's a bmodel
  				if (!surf->insubmodel)
  					goto continue_search;
  
  			// must be two bmodels in the same leaf; sort on 1/z
  				fu = (float)(edge->u - 0xFFFFF) * (1.0 / 0x100000);
  				newzi = surf->d_ziorigin + fv*surf->d_zistepv +
  						fu*surf->d_zistepu;
  				newzibottom = newzi * 0.99;
  
  				testzi = surf2->d_ziorigin + fv*surf2->d_zistepv +
  						fu*surf2->d_zistepu;
  
  				if (newzibottom >= testzi)
  				{
  					goto gotposition;
  				}
  
  				newzitop = newzi * 1.01;
  				if (newzitop >= testzi)
  				{
  					if (surf->d_zistepu >= surf2->d_zistepu)
  					{
  						goto gotposition;
  					}
  				}
  
  				goto continue_search;
  			}
  
  			goto gotposition;
  
  newtop:
  		// emit a span (obscures current top)
  			iu = edge->u >> 20;
  
  			if (iu > surf2->last_u)
  			{
  				span = span_p++;
  				span->u = surf2->last_u;
  				span->count = iu - span->u;
  				span->v = current_iv;
  				span->pnext = surf2->spans;
  				surf2->spans = span;
  			}
  
  			// set last_u on the new span
  			surf->last_u = iu;
  				
  gotposition:
  		// insert before surf2
  			surf->next = surf2;
  			surf->prev = surf2->prev;
  			surf2->prev->next = surf;
  			surf2->prev = surf;
  		}
  	}
  }
  
  
  /*
  ==============
  R_GenerateSpans
  ==============
  */
  void R_GenerateSpans (void)
  {
  	edge_t			*edge;
  	surf_t			*surf;
  
  	r_bmodelactive = 0;
  
  // clear active surfaces to just the background surface
  	surfaces[1].next = surfaces[1].prev = &surfaces[1];
  	surfaces[1].last_u = edge_head_u_shift20;
  
  // generate spans
  	for (edge=edge_head.next ; edge != &edge_tail; edge=edge->next)
  	{			
  		if (edge->surfs[0])
  		{
  		// it has a left surface, so a surface is going away for this span
  			surf = &surfaces[edge->surfs[0]];
  
  			R_TrailingEdge (surf, edge);
  
  			if (!edge->surfs[1])
  				continue;
  		}
  
  		R_LeadingEdge (edge);
  	}
  
  	R_CleanupSpan ();
  }
  
  #endif	// !id386
  
  
  /*
  ==============
  R_GenerateSpansBackward
  ==============
  */
  void R_GenerateSpansBackward (void)
  {
  	edge_t			*edge;
  
  	r_bmodelactive = 0;
  
  // clear active surfaces to just the background surface
  	surfaces[1].next = surfaces[1].prev = &surfaces[1];
  	surfaces[1].last_u = edge_head_u_shift20;
  
  // generate spans
  	for (edge=edge_head.next ; edge != &edge_tail; edge=edge->next)
  	{			
  		if (edge->surfs[0])
  			R_TrailingEdge (&surfaces[edge->surfs[0]], edge);
  
  		if (edge->surfs[1])
  			R_LeadingEdgeBackwards (edge);
  	}
  
  	R_CleanupSpan ();
  }
  
  
  /*
  ==============
  R_ScanEdges
  
  Input: 
  newedges[] array
  	this has links to edges, which have links to surfaces
  
  Output:
  Each surface has a linked list of its visible spans
  ==============
  */
  void R_ScanEdges (void)
  {
  	int		iv, bottom;
  	byte	basespans[MAXSPANS*sizeof(espan_t)+CACHE_SIZE];
  	espan_t	*basespan_p;
  	surf_t	*s;
  
  	basespan_p = (espan_t *)
  			((long)(basespans + CACHE_SIZE - 1) & ~(CACHE_SIZE - 1));
  	max_span_p = &basespan_p[MAXSPANS - r_refdef.vrect.width];
  
  	span_p = basespan_p;
  
  // clear active edges to just the background edges around the whole screen
  // FIXME: most of this only needs to be set up once
  	edge_head.u = r_refdef.vrect.x << 20;
  	edge_head_u_shift20 = edge_head.u >> 20;
  	edge_head.u_step = 0;
  	edge_head.prev = NULL;
  	edge_head.next = &edge_tail;
  	edge_head.surfs[0] = 0;
  	edge_head.surfs[1] = 1;
  	
  	edge_tail.u = (r_refdef.vrectright << 20) + 0xFFFFF;
  	edge_tail_u_shift20 = edge_tail.u >> 20;
  	edge_tail.u_step = 0;
  	edge_tail.prev = &edge_head;
  	edge_tail.next = &edge_aftertail;
  	edge_tail.surfs[0] = 1;
  	edge_tail.surfs[1] = 0;
  	
  	edge_aftertail.u = -1;		// force a move
  	edge_aftertail.u_step = 0;
  	edge_aftertail.next = &edge_sentinel;
  	edge_aftertail.prev = &edge_tail;
  
  // FIXME: do we need this now that we clamp x in r_draw.c?
  	edge_sentinel.u = 2000 << 24;		// make sure nothing sorts past this
  	edge_sentinel.prev = &edge_aftertail;
  
  //	
  // process all scan lines
  //
  	bottom = r_refdef.vrectbottom - 1;
  
  	for (iv=r_refdef.vrect.y ; iv<bottom ; iv++)
  	{
  		current_iv = iv;
  		fv = (float)iv;
  
  	// mark that the head (background start) span is pre-included
  		surfaces[1].spanstate = 1;
  
  		if (newedges[iv])
  		{
  			R_InsertNewEdges (newedges[iv], edge_head.next);
  		}
  
  		(*pdrawfunc) ();
  
  	// flush the span list if we can't be sure we have enough spans left for
  	// the next scan
  		if (span_p > max_span_p)
  		{
  			VID_UnlockBuffer ();
  			S_ExtraUpdate ();	// don't let sound get messed up if going slow
  			VID_LockBuffer ();
  		
  			if (r_drawculledpolys)
  				R_DrawCulledPolys ();
  			else
  				D_DrawSurfaces ();
  
  		// clear the surface span pointers
  			for (s = &surfaces[1] ; s<surface_p ; s++)
  				s->spans = NULL;
  
  			span_p = basespan_p;
  		}
  
  		if (removeedges[iv])
  			R_RemoveEdges (removeedges[iv]);
  
  		if (edge_head.next != &edge_tail)
  			R_StepActiveU (edge_head.next);
  	}
  
  // do the last scan (no need to step or sort or remove on the last scan)
  
  	current_iv = iv;
  	fv = (float)iv;
  
  // mark that the head (background start) span is pre-included
  	surfaces[1].spanstate = 1;
  
  	if (newedges[iv])
  		R_InsertNewEdges (newedges[iv], edge_head.next);
  
  	(*pdrawfunc) ();
  
  // draw whatever's left in the span list
  	if (r_drawculledpolys)
  		R_DrawCulledPolys ();
  	else
  		D_DrawSurfaces ();
  }
  
  
  