initial commit

README.md

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+# Spinning donut
+
+Source: https://www.a1k0n.net/2011/07/20/donut-math.html

donut.c

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+#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;
+	}
+}