lib/gfxpoly/stroke.c

   1 #include <stdlib.h>
   2 #include <stdio.h>
   3 #include <math.h>
   4 #include "../gfxdevice.h"
   5 #include "../gfxtools.h"
   6 #include "poly.h"
   7 #include "wind.h"
   8 #include "convert.h"
   9
  10 /* notice: left/right for a coordinate system where y goes up, not down */
  11 typedef enum {LEFT=0, RIGHT=1} leftright_t;
  12
  13 /* factor that determines into how many line fragments a spline is converted */
  14 #define SUBFRACTION (2.4)
  15
  16 // spline equation:
  17 // s(t) = t*t*x2 + 2*t*(1-t)*cx + (1-t)*(1-t)*x1
  18 //
  19 // s(0.5) = 0.25*x2 + 0.5*cx + 0.25*x1
  20 // ds(t)/dt = 2*t*x2 + (2-2t)*cx + (2t-2)*x1
  21 // ds(0) = 2*(cx-x1)
  22
  23 static void draw_arc(gfxdrawer_t*draw, double x, double y, double a1, double a2, double r)
  24 {
  25     if(a2<a1) a2+=M_PI*2;
  26
  27     double d = (a2-a1);
  28     int steps = ceil(8*d/(M_PI*2)); // we use 8 splines for a full circle
  29     if(!steps) return;
  30
  31     int t;
  32     double step = (a2-a1)/steps;
  33     double lastx = x+cos(a1)*r;
  34     double lasty = y+sin(a1)*r;
  35
  36     /* we could probably build a table for this- there are only 8
  37        possible values for step */
  38     double r2 = r*(2-sqrt(0.5+0.5*cos(step)));
  39
  40     draw->lineTo(draw, x+cos(a1)*r,y+sin(a1)*r);
  41     for(t=1;t<=steps;t++) {
  42         double a = a1 + t*step;
  43         double c = cos(a)*r;
  44         double s = sin(a)*r;
  45         double xx = c + x;
  46         double yy = s + y;
  47         double dx = x + cos(a-step/2)*r2;
  48         double dy = y + sin(a-step/2)*r2;
  49         draw->splineTo(draw, dx, dy, xx, yy);
  50         lastx = xx;
  51         lasty = yy;
  52     }
  53 }
  54
  55 static void draw_single_stroke(gfxpoint_t*p, int num, gfxdrawer_t*draw, double width, gfx_capType cap, gfx_joinType join, double limit)
  56 {
  57     width/=2;
  58     if(width<=0)
  59         width = 0.05;
  60
  61     /* remove duplicate points */
  62     int s=1,t;
  63     gfxpoint_t last = p[0];
  64     for(t=1;t<num;t++) {
  65         if(p[t].x != last.x || p[t].y != last.y) {
  66             p[s++] = last = p[t];
  67         }
  68     }
  69     num = s;
  70
  71     char closed = (num>2 && p[0].x == p[num-1].x && p[0].y == p[num-1].y);
  72
  73     int start = 0;
  74     int end = num-1;
  75     int incr = 1;
  76     int pos = 0;
  77
  78     double lastw=0;
  79     /* iterate through the points two times: first forward, then backward,
  80        adding a stroke outline to the right side and line caps after each
  81        pass */
  82     int pass;
  83     for(pass=0;pass<2;pass++) {
  84         if(closed) {
  85             double dx = p[end].x - p[end-incr].x;
  86             double dy = p[end].y - p[end-incr].y;
  87             lastw = atan2(dy,dx);
  88             if(lastw<0) lastw+=M_PI*2;
  89         }
  90
  91         int pos;
  92         for(pos=start;pos!=end;pos+=incr) {
  93             //printf("%d) %.2f %.2f\n", pos, p[pos].x, p[pos].y);
  94             double dx = p[pos+incr].x - p[pos].x;
  95             double dy = p[pos+incr].y - p[pos].y;
  96             double w = atan2(dy,dx);
  97             if(w<0) w+=M_PI*2;
  98
  99             if(closed || pos!=start) {
 100                 double d = w-lastw;
 101                 leftright_t turn;
 102                 if(d>=0 && d<M_PI) turn=LEFT;
 103                 else if(d<0 && d>-M_PI) turn=RIGHT;
 104                 else if(d>=M_PI) {turn=RIGHT;}
 105                 else if(d<=-M_PI) {turn=LEFT;d+=M_PI*2;}
 106                 else {assert(0);}
 107                 if(turn!=LEFT || join==gfx_joinBevel) {
 108                     // nothing to do. bevel joins are easy
 109                 } else if(join==gfx_joinRound) {
 110                     draw_arc(draw, p[pos].x, p[pos].y, lastw-M_PI/2, w-M_PI/2, width);
 111                 } else if(join==gfx_joinMiter) {
 112                     double xw = M_PI/2 - d/2;
 113                     if(xw>0) {
 114                         double r2 = 1.0 / sin(M_PI/2-d/2);
 115                         if(r2 < limit) {
 116                             r2 *= width;
 117                             double addx = cos(lastw-M_PI/2+d/2)*r2;
 118                             double addy = sin(lastw-M_PI/2+d/2)*r2;
 119                             draw->lineTo(draw, p[pos].x+addx, p[pos].y+addy);
 120                         }
 121                     }
 122                 }
 123             }
 124
 125             double addx = cos(w-M_PI/2)*width;
 126             double addy = sin(w-M_PI/2)*width;
 127             draw->lineTo(draw, p[pos].x+addx, p[pos].y+addy);
 128             double px2 = p[pos+incr].x + addx;
 129             double py2 = p[pos+incr].y + addy;
 130             draw->lineTo(draw, p[pos+incr].x+addx, p[pos+incr].y+addy);
 131             lastw = w;
 132         }
 133
 134         if(closed) {
 135             draw->close(draw);
 136         } else {
 137             /* draw stroke ends. We draw duplicates of some points here. The drawer
 138                implementation should be smart enough to remove them. */
 139             double c = cos(lastw-M_PI/2)*width;
 140             double s = sin(lastw-M_PI/2)*width;
 141             if(cap == gfx_capButt) {
 142                 draw->lineTo(draw, p[pos].x+c, p[pos].y+s);
 143                 draw->lineTo(draw, p[pos].x-c, p[pos].y-s);
 144             } else if(cap == gfx_capRound) {
 145                 draw_arc(draw, p[pos].x, p[pos].y, lastw-M_PI/2, lastw+M_PI/2, width);
 146             } else if(cap == gfx_capSquare) {
 147                 double c = cos(lastw-M_PI/2)*width;
 148                 double s = sin(lastw-M_PI/2)*width;
 149                 draw->lineTo(draw, p[pos].x+c, p[pos].y+s);
 150                 draw->lineTo(draw, p[pos].x+c-s, p[pos].y+s+c);
 151                 draw->lineTo(draw, p[pos].x-c-s, p[pos].y-s+c);
 152                 draw->lineTo(draw, p[pos].x-c, p[pos].y-s);
 153             }
 154             lastw += M_PI; // for dots
 155         }
 156         start=num-1;
 157         end=0;
 158         incr=-1;
 159     }
 160     if(!closed)
 161         draw->close(draw);
 162 }
 163
 164 void draw_stroke(gfxline_t*start, gfxdrawer_t*draw, double width, gfx_capType cap, gfx_joinType join, double miterLimit)
 165 {
 166     if(!start)
 167         return;
 168     assert(start->type == gfx_moveTo);
 169     gfxline_t*line = start;
 170     // measure array size
 171     int size = 0;
 172     int pos = 0;
 173     double lastx,lasty;
 174     while(line) {
 175         if(line->type == gfx_moveTo) {
 176             if(pos>size) size = pos;
 177             pos++;
 178         } else if(line->type == gfx_lineTo) {
 179             pos++;
 180         } else if(line->type == gfx_splineTo) {
 181             int parts = (int)(sqrt(fabs(line->x-2*line->sx+lastx) + fabs(line->y-2*line->sy+lasty))*SUBFRACTION);
 182             if(!parts) parts = 1;
 183             pos+=parts+1;
 184         }
 185         lastx = line->x;
 186         lasty = line->y;
 187         line = line->next;
 188     }
 189     if(pos>size) size = pos;
 190     if(!size) return;
 191
 192     gfxpoint_t* points = malloc(sizeof(gfxpoint_t)*size);
 193     line = start;
 194     pos = 0;
 195     while(line) {
 196         if(line->type == gfx_moveTo) {
 197             if(pos)
 198                 draw_single_stroke(points, pos, draw, width, cap, join, miterLimit);
 199             pos = 0;
 200         } else if(line->type == gfx_splineTo) {
 201             int parts = (int)(sqrt(fabs(line->x-2*line->sx+lastx) + fabs(line->y-2*line->sy+lasty))*SUBFRACTION);
 202             if(!parts) parts = 1;
 203             double stepsize = 1.0/parts;
 204             int i;
 205             for(i=0;i<parts;i++) {
 206                 double t = (double)i*stepsize;
 207                 points[pos].x = (line->x*t*t + 2*line->sx*t*(1-t) + lastx*(1-t)*(1-t));
 208                 points[pos].y = (line->y*t*t + 2*line->sy*t*(1-t) + lasty*(1-t)*(1-t));
 209                 pos++;
 210             }
 211         }
 212         lastx = points[pos].x = line->x;
 213         lasty = points[pos].y = line->y;
 214         pos++;
 215         line = line->next;
 216     }
 217     if(pos) draw_single_stroke(points, pos, draw, width, cap, join, miterLimit);
 218     free(points);
 219 }
 220
 221 static windcontext_t onepolygon = {1};
 222 gfxpoly_t* gfxpoly_from_stroke(gfxline_t*line, gfxcoord_t width, gfx_capType cap_style, gfx_joinType joint_style, gfxcoord_t miterLimit, double gridsize)
 223 {
 224     gfxdrawer_t d;
 225     gfxdrawer_target_poly(&d, gridsize);
 226     draw_stroke(line, &d, width, cap_style, joint_style, miterLimit);
 227     gfxpoly_t*poly = (gfxpoly_t*)d.result(&d);
 228     assert(gfxpoly_check(poly, 1));
 229     gfxpoly_t*poly2 = gfxpoly_process(poly, 0, &windrule_circular, &onepolygon, 0);
 230     gfxpoly_destroy(poly);
 231     return poly2;
 232 }
 233