54 lines
2.5 KiB
C
54 lines
2.5 KiB
C
/* From http://members.chello.at/easyfilter/bresenham.html */
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#include<assert.h>
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#include<stdio.h>
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void setPixel(int x, int y) {
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printf("%d %d\n", x, y);
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}
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void plotQuadBezierSeg(int x0, int y0, int x1, int y1, int x2, int y2)
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{
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int sx = x2-x1, sy = y2-y1;
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long xx = x0-x1, yy = y0-y1, xy=0; /* relative values for checks */
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double dx, dy, err, cur = xx*sy-yy*sx; /* curvature */
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assert(xx*sx <= 0 && yy*sy <= 0); /* sign of gradient must not change */
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printf("A sx %d sy %d xx %ld yy %ld cur %g\n", sx, sy, xx, yy, cur);
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if (sx*(long)sx+sy*(long)sy > xx*xx+yy*yy) { /* begin with longer part */
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printf("swap\n");
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x2 = x0; x0 = sx+x1; y2 = y0; y0 = sy+y1; cur = -cur; /* swap P0 P2 */
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}
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printf("B sx %d sy %d xx %ld yy %ld xy %ld cur %g\n", sx, sy, xx, yy, xy, cur);
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if (cur != 0) { /* no straight line */
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xx += sx; xx *= sx = x0 < x2 ? 1 : -1; /* x step direction */
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yy += sy; yy *= sy = y0 < y2 ? 1 : -1; /* y step direction */
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printf("E sx %d sy %d xx %ld yy %ld xy %ld cur %g\n", sx, sy, xx, yy, xy, cur);
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xy = 2*xx*yy;
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printf("F sx %d sy %d xx %ld yy %ld xy %ld cur %g\n", sx, sy, xx, yy, xy, cur);
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xx *= xx; yy *= yy; /* differences 2nd degree */
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printf("M sx %d sy %d xx %ld yy %ld xy %ld cur %g\n", sx, sy, xx, yy, xy, cur);
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if (cur*sx*sy < 0) { /* negated curvature? */
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printf("negate\n");
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xx = -xx; yy = -yy; xy = -xy; cur = -cur;
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}
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printf("N sx %d sy %d xx %ld yy %ld xy %ld cur %g\n", sx, sy, xx, yy, xy, cur);
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dx = 4.0*sy*cur*(x1-x0)+xx-xy; /* differences 1st degree */
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dy = 4.0*sx*cur*(y0-y1)+yy-xy;
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xx += xx; yy += yy; err = dx+dy+xy; /* error 1st step */
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do {
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printf("%d %d: dx %g dy %g err %g\n", x0, y0, dx, dy, err);
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if (x0 == x2 && y0 == y2) return; /* last pixel -> curve finished */
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y1 = 2*err < dx; /* save value for test of y step */
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if (2*err > dy) { x0 += sx; dx -= xy; err += dy += yy; } /* x step */
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if ( y1 ) { y0 += sy; dy -= xy; err += dx += xx; } /* y step */
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} while (dy < dx ); /* gradient negates -> algorithm fails */
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}
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//? plotLine(x0,y0, x2,y2); /* plot remaining part to end */
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}
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int main(void) {
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plotQuadBezierSeg(0x200, 0x20, 0x180, 0x90, 0x180, 0x160);
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return 0;
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}
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