点を移動したりまわしたり

point.c

#include <stdio.h>
#include <math.h>

typedef struct {
    double x;
    double y;
} point_t;

typedef struct {
    point_t* center;
    double rad;
    double ofs_x;
    double ofs_y;
} config_t;

void to_string(char* str, const point_t* p) {
    sprintf(str, "(x, y) = (%f, %f)\n", p->x, p->y);
}

point_t move(const point_t* p, double x, double y) {
    point_t result = {p->x + x, p->y + y};
    return result;
}

point_t rotate_center(const point_t* p, double rad) {
    point_t result = {
        (p->x) * cos(rad) - (p->y) * sin(rad),
        (p->x) * sin(rad) + (p->y) * cos(rad)
    };
    return result;
}

point_t rotate(const point_t* orig, const point_t* center, double rad) {
    point_t p1 = move(orig, -center->x, -center->y);
    point_t p2 = rotate_center(&p1, rad);
    point_t p3 = move(&p2, center->x, center->y);
    return p3;
}

point_t convert_by_config(const point_t *p, const config_t* conf) {
    point_t p1 = rotate(p, conf->center, conf->rad);
    point_t p2 = move(&p1, conf->ofs_x, conf->ofs_y);
    return p2;
}

double to_rad(double degree) {
    return degree / 180.0 * M_PI;
}

int main(void) {
    point_t p1 = {1.0, 2.0};
    point_t p2 = move(&p1, 2.0, 1.0);
    point_t p3 = rotate_center(&p2, to_rad(45.0));
    config_t conf = {&p1, to_rad(45.0), 1.0, 1.0};
    point_t p4 = convert_by_config(&p1, &conf);
    char str[100];
    to_string(str, &p2);
    printf(str);
    to_string(str, &p3);
    printf(str);
    to_string(str, &p4);
    printf(str);
    return 0;
}