ref: 347303b136c41ac5ca4408818fdd1a3fde89888a
dir: /sys/src/libmemdraw/ellipse.c/
#include <u.h> #include <libc.h> #include <draw.h> #include <memdraw.h> #include <memlayer.h> /* * ellipse(dst, c, a, b, t, src, sp) * draws an ellipse centered at c with semiaxes a,b>=0 * and semithickness t>=0, or filled if t<0. point sp * in src maps to c in dst * * very thick skinny ellipses are brushed with circles (slow) * others are approximated by filling between 2 ellipses * criterion for very thick when b<a: t/b > 0.5*x/(1-x) * where x = b/a */ typedef struct Param Param; typedef struct State State; static void bellipse(int, State*, Param*); static void erect(int, int, int, int, Param*); static void eline(int, int, int, int, Param*); struct Param { Memimage *dst; Memimage *src; Point c; int t; Point sp; Memimage *disc; int op; }; /* * denote residual error by e(x,y) = b^2*x^2 + a^2*y^2 - a^2*b^2 * e(x,y) = 0 on ellipse, e(x,y) < 0 inside, e(x,y) > 0 outside */ struct State { int a; int x; vlong a2; /* a^2 */ vlong b2; /* b^2 */ vlong b2x; /* b^2 * x */ vlong a2y; /* a^2 * y */ vlong c1; vlong c2; /* test criteria */ vlong ee; /* ee = e(x+1/2,y-1/2) - (a^2+b^2)/4 */ vlong dxe; vlong dye; vlong d2xe; vlong d2ye; }; static State* newstate(State *s, int a, int b) { s->x = 0; s->a = a; s->a2 = (vlong)(a*a); s->b2 = (vlong)(b*b); s->b2x = (vlong)0; s->a2y = s->a2*(vlong)b; s->c1 = -((s->a2>>2) + (vlong)(a&1) + s->b2); s->c2 = -((s->b2>>2) + (vlong)(b&1)); s->ee = -s->a2y; s->dxe = (vlong)0; s->dye = s->ee<<1; s->d2xe = s->b2<<1; s->d2ye = s->a2<<1; return s; } /* * return x coord of rightmost pixel on next scan line */ static int step(State *s) { while(s->x < s->a) { if(s->ee+s->b2x <= s->c1 || /* e(x+1,y-1/2) <= 0 */ s->ee+s->a2y <= s->c2) { /* e(x+1/2,y) <= 0 (rare) */ s->dxe += s->d2xe; s->ee += s->dxe; s->b2x += s->b2; s->x++; continue; } s->dye += s->d2ye; s->ee += s->dye; s->a2y -= s->a2; if(s->ee-s->a2y <= s->c2) { /* e(x+1/2,y-1) <= 0 */ s->dxe += s->d2xe; s->ee += s->dxe; s->b2x += s->b2; return s->x++; } break; } return s->x; } void memellipse(Memimage *dst, Point c, int a, int b, int t, Memimage *src, Point sp, int op) { State in, out; int y, inb, inx, outx, u; Param p; if(a < 0) a = -a; if(b < 0) b = -b; p.dst = dst; p.src = src; p.c = c; p.t = t; p.sp = subpt(sp, c); p.disc = nil; p.op = op; u = (t<<1)*(a-b); if(b<a && u>b*b || a<b && -u>a*a) { /* if(b<a&&(t<<1)>b*b/a || a<b&&(t<<1)>a*a/b) # very thick */ bellipse(b, newstate(&in, a, b), &p); return; } if(t < 0) { inb = -1; newstate(&out, a, y = b); } else { inb = b - t; newstate(&out, a+t, y = b+t); } if(t > 0) newstate(&in, a-t, inb); inx = 0; for( ; y>=0; y--) { outx = step(&out); if(y > inb) { erect(-outx, y, outx, y, &p); if(y != 0) erect(-outx, -y, outx, -y, &p); continue; } if(t > 0) { inx = step(&in); if(y == inb) inx = 0; } else if(inx > outx) inx = outx; erect(inx, y, outx, y, &p); if(y != 0) erect(inx, -y, outx, -y, &p); erect(-outx, y, -inx, y, &p); if(y != 0) erect(-outx, -y, -inx, -y, &p); inx = outx + 1; } } static Point p00 = {0, 0}; /* * a brushed ellipse */ static void bellipse(int y, State *s, Param *p) { int t, ox, oy, x, nx; t = p->t; p->disc = allocmemimage(Rect(-t,-t,t+1,t+1), GREY1); if(p->disc == nil) return; memfillcolor(p->disc, DTransparent); memellipse(p->disc, p00, t, t, -1, memopaque, p00, p->op); oy = y; ox = 0; nx = x = step(s); do { while(nx==x && y-->0) nx = step(s); y++; eline(-x,-oy,-ox, -y, p); eline(ox,-oy, x, -y, p); eline(-x, y,-ox, oy, p); eline(ox, y, x, oy, p); ox = x+1; x = nx; y--; oy = y; } while(oy > 0); } /* * a rectangle with closed (not half-open) coordinates expressed * relative to the center of the ellipse */ static void erect(int x0, int y0, int x1, int y1, Param *p) { Rectangle r; /* print("R %d,%d %d,%d\n", x0, y0, x1, y1); /**/ r = Rect(p->c.x+x0, p->c.y+y0, p->c.x+x1+1, p->c.y+y1+1); memdraw(p->dst, r, p->src, addpt(p->sp, r.min), memopaque, p00, p->op); } /* * a brushed point similarly specified */ static void epoint(int x, int y, Param *p) { Point p0; Rectangle r; /* print("P%d %d,%d\n", p->t, x, y); /**/ p0 = Pt(p->c.x+x, p->c.y+y); r = Rpt(addpt(p0, p->disc->r.min), addpt(p0, p->disc->r.max)); memdraw(p->dst, r, p->src, addpt(p->sp, r.min), p->disc, p->disc->r.min, p->op); } /* * a brushed horizontal or vertical line similarly specified */ static void eline(int x0, int y0, int x1, int y1, Param *p) { /* print("L%d %d,%d %d,%d\n", p->t, x0, y0, x1, y1); /**/ if(x1 > x0+1) erect(x0+1, y0-p->t, x1-1, y1+p->t, p); else if(y1 > y0+1) erect(x0-p->t, y0+1, x1+p->t, y1-1, p); epoint(x0, y0, p); if(x1-x0 || y1-y0) epoint(x1, y1, p); }