This is a simple method that traverses each row in the image and puts a black pixel at every point that is a Prime number.

private Bitmap CreateNormalPrimeArt(HashSet<int> primes, int width, int height) { Bitmap bmp = new Bitmap(width, height); using (Graphics gfx = Graphics.FromImage(bmp)) { using (Brush brush = new SolidBrush(Color.FromArgb(25, 25, 76))) { gfx.FillRectangle(brush, new Rectangle(0, 0, width, height)); } } for (int y = 0; y < height; y++) { for (int x = 0; x < width; x++) { if (primes.Contains((y * height) + x)) bmp.SetPixel(x, y, Color.White); } } using (Graphics gfx = Graphics.FromImage(bmp)) { using (Brush brush = new SolidBrush(Color.White)) { gfx.DrawString("Prime Rows", new System.Drawing.Font("Calibri", 10), brush, new PointF(20, height - 20)); } } return bmp; }

The second is based on the Ulam Spiral.

private Bitmap CreateUlamSpiralPrimeArt(HashSet<int> primes, int width, int height) { if (width != height) { if (width > height) width = height; else height = width; } if (width % 2 == 0) { width--; height--; } int index = 1; int sideLength = 2; int thisSide = 2; int turns = 0; Bitmap bmp = new Bitmap(width, height); using (Graphics gfx = Graphics.FromImage(bmp)) { using (Brush brush = new SolidBrush(Color.FromArgb(25, 25, 76))) { gfx.FillRectangle(brush, new Rectangle(0, 0, width, height)); } } // set p to center Point p = new Point(width / 2, height / 2); for (int i = 0; i < height; i++) { for (int j = 0; j < width; j++) { if (p.Y <= 5 || p.Y >= height - 5 || p.X <= 5 || p.X >= width - 5) break; if (primes.Contains(index)) bmp.SetPixel(p.X, p.Y, Color.White); index++; thisSide--; int dir = turns % 4; if (thisSide == 0) { thisSide = sideLength; turns++; if (dir == 1 || dir == 3) sideLength += 1; } if (dir == 0) { p.X = p.X + 1; } else if (dir == 1) { p.Y = p.Y - 1; } else if (dir == 2) { p.X = p.X - 1; } else if (dir == 3) { p.Y = p.Y + 1; } } } using (Graphics gfx = Graphics.FromImage(bmp)) { using (Brush brush = new SolidBrush(Color.White)) { gfx.DrawString("Ulam Spiral", new System.Drawing.Font("Calibri", 10), brush, new PointF(20, height - 20)); } } return bmp; }

Third method creates nice spirals based on the Prime distribution. Enjoy.

private Bitmap CreateDSCPrimeArt(HashSet<int> primes, int width, int height) { int index = 1; Bitmap bmp = new Bitmap(width, height); using (Graphics gfx = Graphics.FromImage(bmp)) { using (Brush brush = new SolidBrush(Color.FromArgb(25, 25, 76))) { gfx.FillRectangle(brush, new Rectangle(0, 0, width, height)); } } // set p to center int max = primes.Max(); Point p = new Point(width / 2, height / 2); for (int i = 0; i < height; i++) { for (int j = 0; j < width; j++) { if (primes.Contains(index)) { // calculate location of the next pixel from the center of the image // distance to the center of the image is based on the square root of the prime PointF pixel = new Point() { X = p.X, Y = p.Y }; pixel.X += (float)(Math.Sin(index) * Math.Sqrt(index)); pixel.Y += (float)(Math.Cos(index) * Math.Sqrt(index)); if (!(pixel.Y <= 5 || pixel.Y >= height - 5 || pixel.X <= 5 || pixel.X >= width - 5)) { bmp.SetPixel((int)pixel.X, (int)pixel.Y, Color.White); } } index++; if (index > max) break; } } using (Graphics gfx = Graphics.FromImage(bmp)) { using (Brush brush = new SolidBrush(Color.White)) { gfx.DrawString("Prime Spiral", new System.Drawing.Font("Calibri", 10), brush, new PointF(20, height - 20)); } } return bmp; }

**Update 2017-01-30**

Fixed broken pictures, changed code to a cleaner format without line numbering.

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