Task: Draw a cuboid
C: #include <stdio.h>
#include <stdlib.h>
#include <math.h>
 
const char *shades = ".:!*oe&#%@";
 
void vsub(double *v1, double *v2, double *s) {
	s[0] = v1[0] - v2[0];
	s[1] = v1[1] - v2[1];
	s[2] = v1[2] - v2[2];
}

double normalize(double * v) {
        double len = sqrt(v[0]*v[0] + v[1]*v[1] + v[2]*v[2]);
        v[0] /= len; v[1] /= len; v[2] /= len;
	return len;
}
 
double dot(double *x, double *y) {
        return x[0]*y[0] + x[1]*y[1] + x[2]*y[2];
}

double * cross(double x[3], double y[3], double s[3]) {
	s[0] = x[1] * y[2] - x[2] * y[1];
	s[1] = x[2] * y[0] - x[0] * y[2];
	s[2] = x[0] * y[1] - x[1] * y[0];
	return s;
}

double* madd(double *x, double *y, double d, double *r) {
	r[0] = x[0] + y[0] * d;
	r[1] = x[1] + y[1] * d;
	r[2] = x[2] + y[2] * d;
	return r;
}

double v000[] = { -4, -3, -2 };
double v100[] = {  4, -3, -2 };
double v010[] = { -4,  3, -2 };
double v110[] = {  4,  3, -2 };
double v001[] = { -4, -3,  2 };
double v101[] = {  4, -3,  2 };
double v011[] = { -4,  3,  2 };
double v111[] = {  4,  3,  2 };

typedef struct {
	double * v[4];
	double norm[3];
} face_t;

face_t f[] = {
	{ { v000, v010, v110, v100 }, {  0,  0, -1 } },
	{ { v001, v011, v111, v101 }, {  0,  0,  1 } },
	{ { v000, v010, v011, v001 }, { -1,  0,  0 } },
	{ { v100, v110, v111, v101 }, {  1,  0,  0 } },
	{ { v000, v100, v101, v001 }, {  0, -1,  0 } },
	{ { v010, v110, v111, v011 }, {  0,  1,  0 } },
};

int in_range(double x, double x0, double x1) {
	return (x - x0) * (x - x1) <= 0;
}

int face_hit(face_t *face, double src[3], double dir[3], double hit[3], double *d)
{
	int i;
	double dist;
	for (i = 0; i < 3; i++)
		if (face->norm[i])
			dist = (face->v[0][i] - src[i]) / dir[i];

	madd(src, dir, dist, hit);
	*d = fabs(dot(dir, face->norm) * dist);

	if (face->norm[0]) {
		return  in_range(hit[1], face->v[0][1], face->v[2][1]) &&
			in_range(hit[2], face->v[0][2], face->v[2][2]);
	}
	else if (face->norm[1]) {
		return  in_range(hit[0], face->v[0][0], face->v[2][0]) &&
			in_range(hit[2], face->v[0][2], face->v[2][2]);
	}
	else if (face->norm[2]) {
		return  in_range(hit[0], face->v[0][0], face->v[2][0]) &&
			in_range(hit[1], face->v[0][1], face->v[2][1]);
	}
	return 0;
}

int main()
{
	int i, j, k;
	double eye[3] = { 7, 7, 6 };
	double dir[3] = { -1, -1, -1 }, orig[3] = {0, 0, 0};
	double hit[3], dx[3], dy[3] = {0, 0, 1}, proj[3];
	double d, *norm, dbest, b;
	double light[3] = { 6, 8, 6 }, ldist[3], decay, strength = 10;

 	normalize(cross(eye, dy, dx));
	normalize(cross(eye, dx, dy));

	for (i = -10; i <= 17; i++) {
		for (j = -35; j < 35; j++) {
			vsub(orig, orig, proj);
			madd(madd(proj, dx, j / 6., proj), dy, i/3., proj);
			vsub(proj, eye, dir);
			dbest = 1e100;
			norm = 0;
		 	for (k = 0; k < 6; k++) {
				if (!face_hit(f + k, eye, dir, hit, &d)) continue;
				if (dbest > d) {
					dbest = d;
					norm = f[k].norm;
				}
			}

			if (!norm) {
				putchar(' ');
				continue;
			}

			vsub(light, hit, ldist);
			decay = normalize(ldist);
			b = dot(norm, ldist) / decay * strength;
			if (b < 0) b = 0;
			else if (b > 1) b = 1;
			b += .2;
			if (b > 1) b = 0;
			else b = 1 - b;
			putchar(shades[(int)(b * (sizeof(shades) - 2))]);
		}
		putchar('\n');
	}

        return 0;
}

C#: using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;

namespace Cuboid
{
    public partial class Form1 : Form
    {
        double[][] nodes = {
            new double[] {-1, -1, -1}, new double[] {-1, -1, 1}, new double[] {-1, 1, -1},
            new double[] {-1, 1, 1}, new double[] {1, -1, -1}, new double[] {1, -1, 1},
            new double[] {1, 1, -1}, new double[] {1, 1, 1} };

        int[][] edges = {
            new int[] {0, 1}, new int[] {1, 3}, new int[] {3, 2}, new int[] {2, 0}, new int[] {4, 5},
            new int[] {5, 7}, new int[] {7, 6}, new int[] {6, 4}, new int[] {0, 4}, new int[] {1, 5},
            new int[] {2, 6}, new int[] {3, 7}};

        private int mouseX;
        private int prevMouseX;
        private int prevMouseY;
        private int mouseY;

        public Form1()
        {
            Width = Height = 640;
            StartPosition = FormStartPosition.CenterScreen;
            SetStyle(
                ControlStyles.AllPaintingInWmPaint |
                ControlStyles.UserPaint |
                ControlStyles.DoubleBuffer,
                true);

            MouseMove += (s, e) =>
            {
                prevMouseX = mouseX;
                prevMouseY = mouseY;
                mouseX = e.X;
                mouseY = e.Y;

                double incrX = (mouseX - prevMouseX) * 0.01;
                double incrY = (mouseY - prevMouseY) * 0.01;

                RotateCuboid(incrX, incrY);
                Refresh();
            };

            MouseDown += (s, e) =>
            {
                mouseX = e.X;
                mouseY = e.Y;
            };

            Scale(80, 120, 160);
            RotateCuboid(Math.PI / 5, Math.PI / 9);
        }

        private void RotateCuboid(double angleX, double angleY)
        {
            double sinX = Math.Sin(angleX);
            double cosX = Math.Cos(angleX);

            double sinY = Math.Sin(angleY);
            double cosY = Math.Cos(angleY);

            foreach (var node in nodes)
            {
                double x = node[0];
                double y = node[1];
                double z = node[2];

                node[0] = x * cosX - z * sinX;
                node[2] = z * cosX + x * sinX;

                z = node[2];

                node[1] = y * cosY - z * sinY;
                node[2] = z * cosY + y * sinY;
            }
        }

        private void Scale(int v1, int v2, int v3)
        {
            foreach (var item in nodes)
            {
                item[0] *= v1;
                item[1] *= v2;
                item[2] *= v3;
            }
        }

        protected override void OnPaint(PaintEventArgs args)
        {
            var g = args.Graphics;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.Clear(Color.White);

            g.TranslateTransform(Width / 2, Height / 2);

            foreach (var edge in edges)
            {
                double[] xy1 = nodes[edge[0]];
                double[] xy2 = nodes[edge[1]];
                g.DrawLine(Pens.Black, (int)Math.Round(xy1[0]), (int)Math.Round(xy1[1]),
                        (int)Math.Round(xy2[0]), (int)Math.Round(xy2[1]));
            }

            foreach (var node in nodes)
            {
                g.FillEllipse(Brushes.Black, (int)Math.Round(node[0]) - 4,
                    (int)Math.Round(node[1]) - 4, 8, 8);
            }
        }
    }
}