58 lines
1.5 KiB
C
58 lines
1.5 KiB
C
#include <gint/display.h>
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#include <gint/defs/util.h>
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/* Based on <http://members.chello.at/~easyfilter/bresenham.html> */
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void dellipse(int x1, int y1, int x2, int y2, int fill_color, int border_color)
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{
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if(fill_color == C_NONE && border_color == C_NONE) return;
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if(x1 > x2) swap(x1, x2);
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if(y1 > y2) swap(y1, y2);
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/* Ellipse is completely outside the rendering window */
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if(x1 >= dwindow.right || x2 < dwindow.left) return;
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if(y1 >= dwindow.bottom || y2 < dwindow.top) return;
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int a = x2-x1, b = y2-y1, b1 = b&1; /* diameter */
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int dx = 4*(1-a)*b*b, dy = 4*(b1+1)*a*a; /* error increment */
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int err = dx + dy + b1 * a * a, e2; /* error of 1.step */
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y1 += (b + 1) / 2;
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y2 = y1-b1; /* starting pixel */
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a = 8 * a * a;
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b1 = 8 * b * b;
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do {
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if(fill_color != C_NONE)
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dline(x1, y1, x2, y1, fill_color);
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dpixel(x2, y1, border_color); /* I. Quadrant */
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dpixel(x1, y1, border_color); /* II. Quadrant */
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if(fill_color != C_NONE)
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dline(x1, y2, x2, y2, fill_color);
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dpixel(x1, y2, border_color); /* III. Quadrant */
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dpixel(x2, y2, border_color); /* IV. Quadrant */
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e2 = 2 * err;
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if (e2 <= dy) {
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y1++;
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y2--;
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err += (dy += a);
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}
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if (e2 >= dx || 2 * err > dy) {
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x1++;
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x2--;
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err += (dx += b1);
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}
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}
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while (x1 <= x2);
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while (y1 - y2 <= b) /* to early stop of flat ellipses a=1 */
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{
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dpixel(x1 - 1, y1, border_color); /* finish tip of ellipse */
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dpixel(x2 + 1, y1++, border_color);
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dpixel(x1 - 1, y2, border_color);
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dpixel(x2 + 1, y2--, border_color);
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}
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}
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