OpenGL_Line_Drawing/circle.cpp at main · JacobGH2/OpenGL_Line_Drawing · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
#include "proj.h"

void plot_circle_points(int x, int y, int xt, int yt, int ellipse) {
    drawGSPoint({x+xt, y+yt}, 0, GS_WHITE);
    drawGSPoint({-x+xt, y+yt}, 0, GS_WHITE);
    drawGSPoint({-x+xt, -y+yt}, 0, GS_WHITE);
    drawGSPoint({x+xt, -y+yt}, 0, GS_WHITE);

    if (!ellipse) {
        drawGSPoint({-y+xt, x+yt}, 0, GS_WHITE);
        drawGSPoint({-y+xt, -x+yt}, 0, GS_WHITE);
        drawGSPoint({y+xt, -x+yt}, 0, GS_WHITE);
        drawGSPoint({y+xt, x+yt}, 0, GS_WHITE);
    }
}

void midpoint_circle(int x_true, int y_true, int r) {
    int x = r, y = 0;

    plot_circle_points(x, y, x_true, y_true, 0);
    int P = 1 - r;
    while (x > y) {
        y++;
        if (P <= 0) P = P + 2*y + 1;
        else {
            x--;
            P = P + 2*y - 2*x + 1;
        }
        plot_circle_points(x, y, x_true, y_true, 0);
    }
}

void midpoint_ellipse(int xc, int yc, int rx, int ry) {

    float dx,dy,p1,p2;
    float x = 0, y = ry;

    // P1_0
    p1 = (ry * ry) - (rx*rx*ry) + (.25*rx*rx);
    dx = 2 * ry * ry * x;
    dy = 2 * rx * rx * y;

    while (dx<dy) {
        plot_circle_points(std::round(x), std::round(y), xc, yc, 1); // may need to round, not truncate
        if (p1 < 0) {
            x++;
            dx = dx + (2*ry*ry);
            p1 = p1 + dx + (ry*ry);
        } else {
            x++;
            y--;
            dx = dx + (2*ry*ry);
            dy = dy - (2*rx*rx);
            p1 = p1 + dx - dy + (ry*ry);
        }
    }

    // P2_0
    p2 = ((ry * ry) * ((x + 0.5) * (x + 0.5))) +
        ((rx * rx) * ((y - 1) * (y - 1))) -
        (rx * rx * ry * ry);

    while (y >= 0) {
        plot_circle_points(std::round(x), std::round(y), xc, yc, 1);
        if (p2 > 0) {
            y--;
            dy = dy - (2*rx*rx);
            p2 = p2 + (rx*rx) - dy;
        } else {
            y--;
            x++;
            dx = dx + (2*rx*rx);
            dy = dy - (2*rx*rx);
            p2 = p2 + dx - dy + (rx*rx);
        }
    }
}