Simplified Bresenham's line algorithm: What does it *exactly* do?
int dx = Math.abs(x2 - x1);
int dy = Math.abs(y2 - y1);

int sx = (x1 < x2) ? 1 : -1;
int sy = (y1 < y2) ? 1 : -1;

int err = dx - dy;

while (true) {
    framebuffer.setPixel(x1, y1, Vec3.one);

    if (x1 == x2 && y1 == y2) {
        break;
    }

    int e2 = 2 * err;

    if (e2 > -dy) {
        err = err - dy;
        x1 = x1 + sx;
    }

    if (e2 < dx) {
        err = err + dx;
        y1 = y1 + sy;
    }
}

err = err - dy;
    x1 = x1 + sx;

err = err + dx;
    y1 = y1 + sy;