A segfault bug fixed in polygon.c where it would crash when invalid polygons

[imager.git] / polygon.c

#include "image.h"
#include "draw.h"
#include "log.h"


#define IMTRUNC(x) ((int)((x)*16))

#define coarse(x) ((x)/16)
#define fine(x)   ((x)%16)

#define POLY_DEB(x)



typedef int pcord;

typedef struct {
  int n;
  pcord x,y;
} p_point;

typedef struct {
  int n;
  pcord x1,y1;
  pcord x2,y2;
  pcord miny,maxy;
  pcord minx,maxx;
  int updown; /* -1 means down, 0 vertical, 1 up */
} p_line;

typedef struct {
  int n;
  double x;
} p_slice;

typedef struct {
  int start;
  int stop;
} ss_pair;

typedef struct {
  int *line;		/* temporary buffer for scanline */
  int linelen;		/* length of scanline */
  ss_pair *ss_list;	/* list of start stop linepairs */
  int ssnext;		/* index of the next pair to use */
  int sslen;		/* maximum number of start stop pairs */
} ss_scanline;








static
int
p_compy(const p_point *p1, const p_point *p2) {
  if (p1->y > p2->y) return 1;
  if (p1->y < p2->y) return -1;
  return 0;
}

static
int
p_compx(const p_slice *p1, const p_slice *p2) {
  if (p1->x > p2->x) return 1;
  if (p1->x < p2->x) return -1;
  return 0;
}

/* Change this to int? and round right goddamn it! */

static
double
p_eval_aty(p_line *l, pcord y) {
  int t;
  t=l->y2-l->y1;
  if (t) return ( (y-l->y1)*l->x2 + (l->y2-y)*l->x1 )/t;
  return (l->x1+l->x2)/2.0;
}

static
double
p_eval_atx(p_line *l, pcord x) {
  int t;
  t = l->x2-l->x1;
  if (t) return ( (x-l->x1)*l->y2 + (l->x2-x)*l->y1 )/t;
  return (l->y1+l->y2)/2.0;
}

static
p_line *
line_set_new(double *x, double *y, int l) {
  int i;
  p_line *lset = mymalloc(sizeof(p_line) * l);

  for(i=0; i<l; i++) {
    lset[i].n=i;
    lset[i].x1 = IMTRUNC(x[i]);
    lset[i].y1 = IMTRUNC(y[i]);
    lset[i].x2 = IMTRUNC(x[(i+1)%l]);
    lset[i].y2 = IMTRUNC(y[(i+1)%l]);
    lset[i].miny=min(lset[i].y1,lset[i].y2);
    lset[i].maxy=max(lset[i].y1,lset[i].y2);
    lset[i].minx=min(lset[i].x1,lset[i].x2);
    lset[i].maxx=max(lset[i].x1,lset[i].x2);
  }
  return lset;
}

static
p_point *
point_set_new(double *x, double *y, int l) {
  int i;
  p_point *pset = mymalloc(sizeof(p_point) * l);
  
  for(i=0; i<l; i++) {
    pset[i].n=i;
    pset[i].x=IMTRUNC(x[i]);
    pset[i].y=IMTRUNC(y[i]);
  }
  return pset;
}

static
void
p_line_dump(p_line *l) {
  printf("%d (%d,%d)->(%d,%d) [%d-%d,%d-%d]\n", l->n, l->x1, l->y1, l->x2, l->y2, 
	 l->minx, l->maxx, l->miny, l->maxy);
}


static
void
ss_scanline_reset(ss_scanline *ss) {
  ss->ssnext = 0;
  memset(ss->line, 0, sizeof(int) * ss->linelen);
}

static
void
ss_scanline_init(ss_scanline *ss, int linelen, int linepairs) {
  ss->line    = mymalloc( sizeof(int) * linelen );
  ss->linelen = linelen;
  ss->ss_list = mymalloc( sizeof(ss_pair) * linepairs );
  ss->sslen   = linepairs;
  ss_scanline_reset(ss);
}

static
void
ss_scanline_exorcise(ss_scanline *ss) {
  myfree(ss->line);
  myfree(ss->ss_list);
}
  
		     


/* returns the number of matches */

static
int
lines_in_interval(p_line *lset, int l, p_slice *tllist, pcord cc) {
  int k;
  int count = 0;
  for(k=0; k<l; k++) {
    if (cc >= lset[k].miny && cc <=  lset[k].maxy) {
      if (lset[k].miny == lset[k].maxy) {
	POLY_DEB( printf(" HORIZONTAL - skipped\n") );
      }
      else {
	tllist[count].x=p_eval_aty(&lset[k],cc);
	tllist[count].n=k;
	count++;
      }
    }
  }
  return count;
}

/* marks the up variable for all lines in a slice */

static
void
mark_updown_slices(p_line *lset, p_slice *tllist, int count) {
  p_line *l, *r;
  int k;
  for(k=0; k<count; k+=2) {
    l = lset + tllist[k].n;

    if (l->y1 == l->y2) {
      mm_log((1, "mark_updown_slices: horizontal line being marked: internal error!\n"));
      exit(3);
    }

    l->updown = (l->x1 == l->x2) ?
      0 :
      (l->x1 > l->x2)
      ? 
      (l->y1 > l->y2) ? -1 : 1
      : 
      (l->y1 > l->y2) ? 1 : -1;

    POLY_DEB( printf("marking left line %d as %s(%d)\n", l->n,
		     l->updown ?  l->updown == 1 ? "up" : "down" : "vert", l->updown, l->updown)
	      );

    if (k+1 >= count) {
      mm_log((1, "Invalid polygon spec, odd number of line crossings.\n"));
      return;
    }

    r = lset + tllist[k+1].n;
    if (r->y1 == r->y2) {
      mm_log((1, "mark_updown_slices: horizontal line being marked: internal error!\n"));
      exit(3);
    }

    r->updown = (r->x1 == r->x2) ?
      0 :
      (r->x1 > r->x2)
      ? 
      (r->y1 > r->y2) ? -1 : 1
      : 
      (r->y1 > r->y2) ? 1 : -1;
    
    POLY_DEB( printf("marking right line %d as %s(%d)\n", r->n,
		     r->updown ?  r->updown == 1 ? "up" : "down" : "vert", r->updown, r->updown)
	      );
  }
}



static
unsigned char
saturate(int in) {
  if (in>255) { return 255; }
  else if (in>0) return in;
  return 0;
}


/* This function must be modified later to do proper blending */

void
scanline_flush(i_img *im, ss_scanline *ss, int y, i_color *val) {
  int x, ch, tv;
  i_color t;
  for(x=0; x<im->xsize; x++) {
    tv = saturate(ss->line[x]);
    i_gpix(im, x, y, &t);
    for(ch=0; ch<im->channels; ch++) 
      t.channel[ch] = tv/255.0 * val->channel[ch] + (1.0-tv/255.0) * t.channel[ch];
    i_ppix(im, x, y, &t);
  }
}



static
int
trap_square(pcord xlen, pcord ylen, double xl, double yl) {
  POLY_DEB( printf("trap_square: %d %d %.2f %.2f\n", xlen, ylen, xl, yl) );
  return xlen*ylen-(xl*yl)/2.0;
}


/* 
   pixel_coverage calculates the 'left side' pixel coverage of a pixel that is
   within the min/max ranges.  The shape always corresponds to a square with some
   sort of a triangle cut from it (which can also yield a triangle).
*/


static
int 
pixel_coverage(p_line *line, pcord minx, pcord maxx, pcord  miny, pcord maxy) {
  double lycross, rycross;
  int l, r;

  double xs, ys;
  
  if (!line->updown) {
    l = r = 0;
  } else {
    lycross = p_eval_atx(line, minx);
    rycross = p_eval_atx(line, maxx);
    l = lycross <= maxy && lycross >= miny; /* true if it enters through left side */
    r = rycross <= maxy && rycross >= miny; /* true if it enters through left side */
  }
  POLY_DEB(
 	   printf("%4s(%+d): ", line->updown ?  line->updown == 1 ? "up" : "down" : "vert", line->updown);
	   printf("(%2d,%2d) [%3d-%3d, %3d-%3d] lycross=%.2f rycross=%.2f", coarse(minx), coarse(miny), minx, maxx, miny, maxy, lycross, rycross);
	   printf("    l=%d r=%d\n", l, r)
	   );
  
  if (l && r) 
    return line->updown == 1 ? 
      (double)(maxx-minx) * (2.0*maxy-lycross-rycross)/2.0  /* up case */
      :
      (double)(maxx-minx) * (lycross+rycross-2*miny)/2.0;  /* down case */
  
  if (!l && !r) return (maxy-miny)*(maxx*2-p_eval_aty(line, miny)-p_eval_aty(line, maxy))/2.0;

  if (l && !r)
    return line->updown == 1 ?
      trap_square(maxx-minx, maxy-miny, p_eval_aty(line, miny)-minx, p_eval_atx(line, minx)-miny) : 
      trap_square(maxx-minx, maxy-miny, p_eval_aty(line, maxy)-minx, maxy-p_eval_atx(line, minx));
  

  if (!l && r) {
    int r = line->updown == 1 ?
      (maxx-p_eval_aty(line, maxy))*(maxy-p_eval_atx(line, maxx))/2.0 : 
      (maxx-p_eval_aty(line, miny))*(p_eval_atx(line, maxx)-miny)/2.0;
    return r;
  }
}





/* 
   handle the scanline slice in three steps 
   
   1.  Where only the left edge is inside a pixel
   2a. Where both left and right edge are inside a pixel
   2b. Where neither left or right edge are inside a pixel
   3.  Where only the right edge is inside a pixel
*/

static
void
render_slice_scanline(ss_scanline *ss, int y, p_line *l, p_line *r) {
  
  pcord miny, maxy;	/* y bounds in fine coordinates */
  pcord lminx, lmaxx;	/* left line min/max within y bounds in fine coords */
  pcord rminx, rmaxx;	/* right line min/max within y bounds in fine coords */
  int cpix;		/* x-coordinate of current pixel */
  int thin;		/* boolean for thin/thick segment */
  int startpix;		/* temporary variable for "start of this interval" */
  int stoppix;		/* temporary variable for "end of this interval" */
  int step2end;		/* temporary variable to mark where step2 ends */

  /* Find the y bounds of scanline_slice */

  maxy = min( l->maxy, r->maxy );
  miny = max( l->miny, r->miny );

  maxy = min( maxy, (y+1)*16 );
  miny = max( miny,  y*16 );

  lminx = min( p_eval_aty(l, maxy), p_eval_aty(l, miny) );
  lmaxx = max( p_eval_aty(l, maxy), p_eval_aty(l, miny) );

  rminx = min( p_eval_aty(r, maxy), p_eval_aty(r, miny) );
  rmaxx = max( p_eval_aty(r, maxy), p_eval_aty(r, miny) );

  thin = coarse(lmaxx) >= coarse(rminx);

  startpix = max( coarse(lminx), 0 );
  stoppix  = min( coarse(rmaxx-1), ss->linelen-1 );
  
  for(cpix=startpix; cpix<=stoppix; cpix++) {
    int lt = coarse(lmaxx-1) >= cpix;
    int rt = coarse(rminx) <= cpix;
    
    int A, B, C;
    
    POLY_DEB( printf("(%d,%d) lt=%d rt=%d\n", cpix, y, lt, rt) );

    A = lt ? pixel_coverage(l, cpix*16, cpix*16+16, miny, maxy) : 0;
    B = lt ? 0 : 16*(maxy-miny);
    C = rt ? pixel_coverage(r, cpix*16, cpix*16+16, miny, maxy) : 0;

    POLY_DEB( printf("A=%d B=%d C=%d\n", A, B, C) );

    ss->line[cpix] += A+B-C;

  }
  
}



static
void
render_slice_scanline_old(ss_scanline *ss, int y, p_line *l, p_line *r) {
  
  pcord miny, maxy;	/* y bounds in fine coordinates */
  pcord lminx, lmaxx;	/* left line min/max within y bounds in fine coords */
  pcord rminx, rmaxx;	/* right line min/max within y bounds in fine coords */
  int cpix;		/* x-coordinate of current pixel */
  int thin;		/* boolean for thin/thick segment */
  int startpix;		/* temporary variable for "start of this interval" */
  int stoppix;		/* temporary variable for "end of this interval" */
  int step2end;		/* temporary variable to mark where step2 ends */

  /* Find the y bounds of scanline_slice */

  maxy = min( l->maxy, r->maxy );
  miny = max( l->miny, r->miny );

  maxy = min( maxy, (y+1)*16 );
  miny = max( miny,  y*16 );

  lminx = min( p_eval_aty(l, maxy), p_eval_aty(l, miny) );
  lmaxx = max( p_eval_aty(l, maxy), p_eval_aty(l, miny) );

  rminx = min( p_eval_aty(r, maxy), p_eval_aty(r, miny) );
  rmaxx = max( p_eval_aty(r, maxy), p_eval_aty(r, miny) );

  thin = coarse(lmaxx) >= coarse(rminx);


  /* First step */
  startpix = coarse(lminx);				/* includes tricky starting pixel */
  stoppix  = min(coarse(lmaxx), coarse(rminx) );	/* last pixel is tricky */
  
  /* handle start pixel */

  cpix = startpix;
  if (cpix < stoppix) {
    ss->line[cpix] += pixel_coverage(l, cpix*16, cpix*16+16, miny, maxy);
    printf("%2d: step1 - start pixel\n", cpix);
  }
  
  for(cpix=startpix+1; cpix<stoppix; cpix++) {
    printf("%2d: step1 pixel\n", cpix);
    ss->line[cpix] += l->updown == 1 ? 
      8.0 * (2*maxy-p_eval_atx(l, 16*cpix)-p_eval_atx(l, 16*cpix+16))	/* up case */
      :
      8.0 * (p_eval_atx(l, 16*cpix)+p_eval_atx(l, 16*cpix+16)-2*miny);	/* down case */
  }
  
  
  /* handle stop pixel */

  if (thin) { /* step 2a */
    startpix = coarse(rminx);
    stoppix = coarse(lmaxx+15); /* one more than needed */
    
    for(cpix=startpix; cpix<stoppix; cpix++) {
      printf("%2d: step2a pixel\n", cpix);
      ss->line[cpix] += 
	pixel_coverage(l, cpix*16, cpix*16+16, miny, maxy)
	+(cpix*16+16-min(cpix*16+16, l->maxx))*(maxy-miny)
	-pixel_coverage(r, cpix*16, cpix*16+16, miny, maxy);
    }
  } else { /* step 2b */
    stoppix = coarse(rminx);
    for(/* cpix already correct */; cpix<stoppix; cpix++) {
      printf("%2d: step2b pixel\n", cpix);
      ss->line[cpix] += 16.0*(maxy-miny);
    }
  }
  
  /* step 3 */

  cpix = max(coarse(rminx), coarse(lmaxx+15));
  stoppix = coarse(rmaxx-15);
  
  printf("step3 from %d to %d\n", cpix, stoppix);

  for(; cpix<stoppix; cpix++) {
    printf("%2d: step3 pixel\n", cpix);
    ss->line[cpix] += 0+ 
      (l->updown == 1 ?
       8.0 * (2*maxy-p_eval_atx(r, 16*cpix)-p_eval_atx(r, 16*cpix+16))  /* up case */
       :
       8.0 * (p_eval_atx(r, 16*cpix)+p_eval_atx(r, 16*cpix+16)-2*miny));  /* down case */
  }
  
  ss->line[cpix] += (16.0)*(maxy-miny) - pixel_coverage(r, cpix*16, cpix*16+16, miny, maxy);
}






/* Antialiasing polygon algorithm 
   specs:
   1. only nice polygons - no crossovers
   2. 1/16 pixel resolution
   3. full antialiasing ( complete spectrum of blends )
   4. uses hardly any memory
   5. no subsampling phase
   

   Algorithm outline:
   1. Split into vertical intervals.
   2. handle each interval 

   For each interval we must: 
   1. find which lines are in it
   2. order the lines from in increasing x order.
      since we are assuming no crossovers it is sufficent
      to check a single point on each line.
*/

/*
  Definitions:
  
  1. Interval:  A vertical segment in which no lines cross nor end.
  2. Scanline:  A physical line, contains 16 subpixels in the horizontal direction
  3. Slice:     A start stop line pair.
  
 */


void
i_poly_aa(i_img *im, int l, double *x, double *y, i_color *val) {
  int i ,k;			/* Index variables */
  int clc;			/* Lines inside current interval */
  pcord miny ,maxy;		/* Min and max values of the current slice in the subcord system */
  pcord tempy;
  int cscl;			/* Current scanline */

  ss_scanline templine;		/* scanline accumulator */
  p_point *pset;		/* List of points in polygon */
  p_line  *lset;		/* List of lines in polygon */
  p_slice *tllist;		/* List of slices */

  mm_log((1, "i_poly_aa(im %p, l %d, x %p, y %p, val %p)\n", im, l, x, y, val));

  for(i=0; i<l; i++) {
    mm_log((2, "(%.2f, %.2f)\n", x[i], y[i]));
  }


  POLY_DEB(
	   fflush(stdout);
	   setbuf(stdout, NULL);
	   );

  tllist   = mymalloc(sizeof(p_slice)*l);
  
  ss_scanline_init(&templine, im->xsize, l);

  pset     = point_set_new(x, y, l);
  lset     = line_set_new(x, y, l);


  qsort(pset, l, sizeof(p_point), (int(*)(const void *,const void *))p_compy);
  
  POLY_DEB(
	   for(i=0;i<l;i++) {
	     printf("%d [ %d ] (%d , %d) -> (%d , %d) yspan ( %d , %d )\n",
		    i, lset[i].n, lset[i].x1, lset[i].y1, lset[i].x2, lset[i].y2, lset[i].miny, lset[i].maxy);
	   }
	   printf("MAIN LOOP\n\n");
	   );
  

  /* loop on intervals */
  for(i=0; i<l-1; i++) {
    int startscan = max( coarse(pset[i].y), 0);
    int stopscan = min( coarse(pset[i+1].y+15), im->ysize-1);
    pcord cc = (pset[i].y + pset[i+1].y)/2;

    POLY_DEB(
	     printf("current slice is %d: %d to %d ( cpoint %d ) scanlines %d to %d\n", 
		    i, pset[i].y, pset[i+1].y, cc, startscan, stopscan)
	     );
    
    if (pset[i].y == pset[i+1].y) {
      POLY_DEB( printf("current slice thickness = 0 => skipping\n") );
      continue;
    }
    
    clc = lines_in_interval(lset, l, tllist, cc);
    qsort(tllist, clc, sizeof(p_slice), (int(*)(const void *,const void *))p_compx);

    mark_updown_slices(lset, tllist, clc);

    POLY_DEB( printf("Interval contains %d lines\n", clc) );

    for(k=0; k<clc; k++) {
      int lno = tllist[k].n;
      p_line *ln = lset+lno;
      POLY_DEB(
	       printf("%d:  line #%2d: (%2d, %2d)->(%2d, %2d) (%2d/%2d, %2d/%2d) -> (%2d/%2d, %2d/%2d) alignment=%s\n",
		      k, lno, ln->x1, ln->y1, ln->x2, ln->y2, 
		      coarse(ln->x1), fine(ln->x1), 
		      coarse(ln->y1), fine(ln->y1), 
		      coarse(ln->x2), fine(ln->x2), 
		      coarse(ln->y2), fine(ln->y2),
		      ln->updown == 0 ? "vert" : ln->updown == 1 ? "up" : "down")
	       );
    }
    for(cscl=startscan; cscl<stopscan; cscl++) {
      tempy = min(cscl*16+16, pset[i+1].y);
      POLY_DEB( printf("evaluating scan line %d \n", cscl) );
      for(k=0; k<clc-1; k+=2) {
	render_slice_scanline(&templine, cscl, lset+tllist[k].n, lset+tllist[k+1].n);
      }
      if (16*coarse(tempy) == tempy) {
	POLY_DEB( printf("flushing scan line %d\n", cscl) );
	scanline_flush(im, &templine, cscl, val);
	ss_scanline_reset(&templine);
      }
      /*
	else {
	scanline_flush(im, &templine, cscl, val);
	ss_scanline_reset(&templine);
	return 0;
	}
      */
    }
  } /* Intervals */
  if (16*coarse(tempy) != tempy) 
    scanline_flush(im, &templine, cscl-1, val);

  ss_scanline_exorcise(&templine);
  myfree(pset);
  myfree(lset);
  myfree(tllist);
  
} /* Function */