Mandelbrot in Go 🏃‍♂️

mandelbrot.go

package main

import (
    "os"
    "math"
    "image"
    "flag"
    "image/png"
    "image/color"
)


func scale(value float64, minA float64, maxA float64, minB float64, maxB float64) float64 {
    // Scales a float from number range A to range B.
    return ((value / (math.Abs(minA) + math.Abs(maxA))) * (math.Abs(minB) + math.Abs(maxB))) + minB
}

func mandelbrotColors() [16]color.RGBA {
    // RGBA colors from https://stackoverflow.com/a/16505538
    return [...]color.RGBA {
        color.RGBA{66, 30, 15, 255},
        color.RGBA{25, 7, 26, 255},
        color.RGBA{9, 1, 47, 255},
        color.RGBA{4, 4, 73, 255},
        color.RGBA{0, 7, 100, 255},
        color.RGBA{12, 44, 138, 255},
        color.RGBA{24, 82, 177, 255},
        color.RGBA{57, 125, 209, 255},
        color.RGBA{134, 181, 229, 255},
        color.RGBA{211, 236, 248, 255},
        color.RGBA{241, 244, 191, 255},
        color.RGBA{248, 201, 95, 255},
        color.RGBA{255, 170, 0, 255},
        color.RGBA{204, 128, 0, 255},
        color.RGBA{153, 87, 0, 255},
        color.RGBA{106, 52, 3, 255},
    }
}

func CreateMandelbrotImage(width int, height int, maxIteration int, colors [16]color.RGBA) *image.RGBA {
    // Creates an in memory image and fills it pixel by pixel with mandelbrotColors
    mandelbrotImage := image.NewRGBA(image.Rect(0, 0, width, height))

    // Implementation of https://en.wikipedia.org/wiki/Mandelbrot_set#Escape_time_algorithm
    for Px := 0; Px < width; Px++ {
        for Py := 0; Py < height; Py++ {
            var x0 float64 = scale(float64(Px), 0, float64(width), -2.5, 1);
            var y0 float64 = scale(float64(Py), 0, float64(height), -1, 1);

            var x, y float64 = 0, 0;
            iteration := 0;
            for ; x*x + y*y < 2*2 && iteration < maxIteration; iteration++ {
                xTemp := x*x - y*y + x0;
                y = 2*x*y + y0;
                x = xTemp;
            }
            color := colors[(iteration % len(colors))]
            mandelbrotImage.Set(Px, Py, color)
        }    
    }

    return mandelbrotImage
}


func main() {
    var width, height, iteration int
    flag.IntVar(&width, "w", 1000, "specify width to use.  defaults to 1024.")
    flag.IntVar(&height, "h", 600, "specify height to use.  defaults to 1024.")
    flag.IntVar(&iteration, "i", 10, "specify iterations to use.  defaults to 40.")
    flag.Parse()

    img := CreateMandelbrotImage(width, height, iteration, mandelbrotColors())
    file, err := os.Create("mandelbrot.png")
    if err != nil {
        panic(err)
    }
    defer file.Close()
    png.Encode(file, img)

}