Quadratic bezier curve rasterization

#include <stdio.h>
#include <assert.h>
#include <algorithm>
using namespace std;

//==============================
#include "loadbmp.h"
Bitmap bmp;
void DrawPixel(int x, int y) {
    int pixel = y * bmp.width + x;
    auto ptr = bmp.buffer + (bmp.bpp/8) * pixel;
    ptr[0] = ptr[1] = ptr[2] = 255;
}
//==============================


struct Point {
    union {
        struct { double x, y; };
        double a[2];
    };
};

struct Bezier {
    Point pts[3];
};

const double EPS = 1e-7;
const double INF = 1e+50;

double WhenEquals(double p0, double p1, double p2, double val, double minp) {
    //p0 * (1-t)^2 + p1 * 2t(1 - t) + p2 * t^2 = val
    double qa = p0 + p2 - 2 * p1;
    double qb = p1 - p0;
    double qc = p0 - val;
    assert(fabs(qa) > EPS); //singular case must be handled separately
    double qd = qb * qb - qa * qc;
    if (qd < -EPS)
        return INF;
    qd = sqrt(max(qd, 0.0));
    double t1 = (-qb - qd) / qa;
    double t2 = (-qb + qd) / qa;
    if (t2 < t1) swap(t1, t2);
    if (t1 > minp + EPS)
        return t1;
    else if (t2 > minp + EPS)
        return t2;
    return INF;
}

void DrawCurve(const Bezier &curve) {
    int cell[2];
    for (int c = 0; c < 2; c++)
        cell[c] = int(floor(curve.pts[0].a[c]));
    DrawPixel(cell[0], cell[1]);
    double param = 0.0;
    while (1) {
        int bc = -1, bs = -1;
        double bestTime = 1.0;
        for (int c = 0; c < 2; c++)
            for (int s = 0; s < 2; s++) {
                double crit = WhenEquals(
                    curve.pts[0].a[c],
                    curve.pts[1].a[c],
                    curve.pts[2].a[c],
                    cell[c] + s, param
                );
                if (crit < bestTime) {
                    bestTime = crit;
                    bc = c, bs = s;
                }
            }
        if (bc < 0)
            break;
        param = bestTime;
        cell[bc] += (2*bs - 1);
        DrawPixel(cell[0], cell[1]);
    }
}

int main() {
    bmp = Bitmap(24, 100, 100);
    bmp.alloc();
    memset(bmp.buffer, 0, bmp.size());

    Bezier crv;
    crv.pts[0].x = 10.1;
    crv.pts[0].y = 10.2;
    crv.pts[1].x = 70.1;
    crv.pts[1].y = 110.3;
    crv.pts[2].x = 70.4;
    crv.pts[2].y = 30.1;
    DrawCurve(crv);

    SaveBMP(bmp, "res.bmp", 24);
}