#include "math.h"
#include "stdio.h"

const float theta_spacing = 0.07;
const float phi_spacing = 0.02;

const int screen_width = 50;
const int screen_height = 50;

const float R1 = 1;
const float R2 = 2;
const float K2 = 5;
const float K1 = screen_width*K2*3/(8*(R1+R2));

void render_frame(float A, float B) {
	// Pre compute values that are used a lot
	float cosA = cosf(A), sinA = sinf(A);
	float cosB = cosf(B), sinB = sinf(B);

	// Create output and depth buffers
	char output[screen_width][screen_height];
	float zbuffer[screen_width][screen_height];

	// Initialize output and depth buffers to zero
	for (int i = 0; i < screen_width; i++) {
		for (int j = 0; j < screen_height; j++) {
			output[i][j] = ' ';
			zbuffer[i][j] = 0;
		}
	}

	for (float theta=0; theta < 2*M_PI; theta += theta_spacing) {
		float costheta = cosf(theta), sintheta = sinf(theta);

		for (float phi = 0; phi < 2*M_PI; phi += phi_spacing) {
			float cosphi = cosf(phi), sinphi = sinf(phi);

			float circlex = R2 + R1*costheta;
			float circley = R1*sintheta;

			float x = circlex*(cosB*cosphi + sinA*sinB*sinphi) - circley*cosA*cosB;
			float y = circlex*(sinB*cosphi - sinA*cosB*sinphi) + circley*cosA*cosB;
			float z = K2 + cosA*circlex*sinphi + circley*sinA;
			float ooz = 1/z; // "one over z"

			int xp = (int) ((float)screen_width/2 + K1*ooz*x);
			int yp = (int) ((float)screen_height/2 - K1*ooz*y);

			float L = cosphi*costheta*sinB - cosA*costheta*sinA*sinphi - sinA*sintheta + cosB*(cosA*sintheta - costheta*sinA*sinphi);
			if (L > 0) {
				if (ooz > zbuffer[yp][xp]) {
					zbuffer[yp][xp] = ooz;
					int luminance_index = L*8;
					output[yp][xp] = ".,-~:;=!*#$@"[luminance_index];
				}
			}
		}
	}

	printf("\x1b[H");
	for (int j = 0; j < screen_height; j++) {
		for (int i = 0; i < screen_width; i++) {
			putchar(output[i][j]);
		}
		putchar('\n');
	}
}

int main() {
	float A = 0;
	float B = 0;
	while (1) {
		render_frame(A, B);
		A += 0.04/20;
		B += 0.02/20;
	}
}