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