转自知乎用C语言献爱心

转自知乎：http://www.zhihu.com/question/20187195

下面这个3D的红心贼犀利：

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

float f(float x, float y, float z) {
    float a = x * x + 9.0f / 4.0f * y * y + z * z – 1;
    return a * a * a – x * x * z * z * z – 9.0f / 80.0f * y * y * z * z * z;
}

float h(float x, float z) {
    float y;
    for (y = 1.0f; y >= 0.0f; y -= 0.001f)
        if (f(x, y, z) <= 0.0f)
            return y;
    return 0.0f;
}

int main() {
    float z;
    for (z = 1.5f; z > -1.5f; z -= 0.05f) {
        float x;
        for (x = -1.5f; x < 1.5f; x += 0.025f) {
            float v = f(x, 0.0f, z);
            if (v <= 0.0f) {
                float y0 = h(x, z);
                float ny = 0.01f;
                float nx = h(x + ny, z) – y0;
                float nz = h(x, z + ny) – y0;
                float nd = 1.0f / sqrtf(nx * nx + ny * ny + nz * nz);
                float d = (nx + ny – nz) * nd * 0.5f + 0.5f;
                putchar(“.:-=+*#%@”[(int)(d * 5.0f)]);
            }
            else
                putchar(‘ ‘);
        }
        putchar(‘\n’);
    }
}