118 lines
2.3 KiB
Plaintext
Executable File
118 lines
2.3 KiB
Plaintext
Executable File
// reference: https://zhuanlan.zhihu.com/p/30748318
|
|
|
|
const int W = 192, H = 192, N = 24;
|
|
|
|
const float PI = 3.14159265359, TWO_PI = 6.28318530718;
|
|
const int MAX_STEP = 10;
|
|
const float MAX_DISTANCE = 2.0;
|
|
const float EPSILON = 1e-6;
|
|
|
|
const int RAND_MAX = 100000007 - 1;
|
|
int seed = 0;
|
|
|
|
int rand() {
|
|
seed = (seed * 19980130 + 23333) % 100000007;
|
|
if (seed < 0) seed = seed + 100000007;
|
|
return seed;
|
|
}
|
|
|
|
float my_fabs(float x) {
|
|
if (x > 0) return x;
|
|
return -x;
|
|
}
|
|
|
|
float my_sqrt(float x) {
|
|
float t = x / 8 + 0.5 + 2 * x / (4 + x);
|
|
int c = 10;
|
|
while (c) {
|
|
t = (t + x / t) / 2;
|
|
c = c - 1;
|
|
}
|
|
return t;
|
|
}
|
|
|
|
float p(float x) { return 3 * x - 4 * x * x * x; }
|
|
|
|
float my_sin_impl(float x) {
|
|
if (my_fabs(x) <= EPSILON) return x;
|
|
return p(my_sin_impl(x / 3.0));
|
|
}
|
|
|
|
float my_sin(float x) {
|
|
if (x > TWO_PI || x < -TWO_PI) {
|
|
int xx = x / TWO_PI;
|
|
x = x - xx * TWO_PI;
|
|
}
|
|
if (x > PI) x = x - TWO_PI;
|
|
if (x < -PI) x = x + TWO_PI;
|
|
return my_sin_impl(x);
|
|
}
|
|
|
|
float my_cos(float x) { return my_sin(x + PI / 2); }
|
|
|
|
float circle_sdf(float x, float y, float cx, float cy, float r) {
|
|
float ux = x - cx, uy = y - cy;
|
|
return my_sqrt(ux * ux + uy * uy) - r;
|
|
}
|
|
|
|
void scene(float x, float y, float ret[]) {
|
|
float sd0 = circle_sdf(x, y, 0.4, 0.4, 0.10),
|
|
sd1 = circle_sdf(x, y, 0.6, 0.6, 0.05);
|
|
if (sd0 < sd1) {
|
|
ret[0] = sd0;
|
|
ret[1] = 3.0;
|
|
} else {
|
|
ret[0] = sd1;
|
|
ret[1] = 0.0;
|
|
}
|
|
}
|
|
|
|
float trace(float ox, float oy, float dx, float dy) {
|
|
float t = 0.0;
|
|
int i = 0;
|
|
while (i < MAX_STEP && t < MAX_DISTANCE) {
|
|
float ret[2];
|
|
scene(ox + dx * t, oy + dy * t, ret);
|
|
if (ret[0] < EPSILON) return ret[1];
|
|
t = t + ret[0];
|
|
i = i + 1;
|
|
}
|
|
return 0.0;
|
|
}
|
|
|
|
float sample(float x, float y) {
|
|
float sum = 0.0;
|
|
int i = 0;
|
|
while (i < N) {
|
|
float rnd = rand();
|
|
float a = TWO_PI * (i + rnd / RAND_MAX) / N;
|
|
sum = sum + trace(x, y, my_cos(a), my_sin(a));
|
|
i = i + 1;
|
|
}
|
|
return sum / N;
|
|
}
|
|
|
|
void write_pgm() {
|
|
putch(80); putch(50); putch(10); // P2
|
|
putint(W); putch(32); putint(H); putch(32); putint(255); putch(10); // W H 255
|
|
int y = 0;
|
|
while (y < H) {
|
|
int x = 0;
|
|
while (x < W) {
|
|
float xx = x, yy = y;
|
|
int p = sample(xx / W, yy / H) * 255.0;
|
|
if (p > 255) p = 255;
|
|
putint(p);
|
|
putch(32);
|
|
x = x + 1;
|
|
}
|
|
putch(10);
|
|
y = y + 1;
|
|
}
|
|
}
|
|
|
|
int main() {
|
|
write_pgm();
|
|
return 0;
|
|
}
|