xyproto/mandel

Fractal renderers

Mandel

Two short Go programs that demonstrates the use of concurrency and goroutines for rendering a Mandelbrot fractal and a slice of a Mandelbulb fractal.

Each row is rendered in a goroutine, where they are spawned with the go keyword. sync.WaitGroup is used to wait for the gorutines to complete. Only the Go standard library is used, for both programs.

Screenshots

Mandelbrot

This image is rendered at 3840x2160 and takes around 2 seconds to render on my laptop.

Mandelbulb

This image is rendered at 3840x2160 and then scaled down to 1920x1080. It takes around 12 seconds to render on my laptop.

Source code

Mandelbrot

package main

import (
    "fmt"
    "image"
    "image/color"
    "image/png"
    "math/cmplx"
    "os"
    "sync"
)

const (
    width      = 3840
    height     = 2160
    xmin, ymin = -2, -1
    xmax, ymax = 1, 1
    maxIter    = 1000
)

var wg sync.WaitGroup

// mandelbrot calculates the color of a point in the Mandelbrot set.
func mandelbrot(c complex128) color.Color {
    z := c
    for i := 0; i < maxIter; i++ {
        if cmplx.Abs(z) > 2 {
            return color.Gray{uint8(255 - i%256)}
        }
        z = z*z + c
    }
    return color.Black
}

// renderRow renders a single row of the Mandelbrot set.
func renderRow(img *image.RGBA, y int) {
    defer wg.Done()
    for x := 0; x < width; x++ {
        c := complex(
            float64(x)/width*(xmax-xmin)+xmin,
            float64(y)/height*(ymax-ymin)+ymin)
        color := mandelbrot(c)
        img.Set(x, y, color)
    }
}

func main() {
    img := image.NewRGBA(image.Rect(0, 0, width, height))

    for y := 0; y < height; y++ {
        wg.Add(1)
        go renderRow(img, y)
    }

    wg.Wait()

    file, err := os.Create("mandelbrot.png")
    if err != nil {
        fmt.Println("Error creating file:", err)
        return
    }
    defer file.Close()

    err = png.Encode(file, img)
    if err != nil {
        fmt.Println("Error encoding image:", err)
    }
}

Mandelbulb

package main

import (
    "fmt"
    "image"
    "image/color"
    "image/png"
    "math"
    "os"
    "sync"
)

const (
    width, height      = 1920, 1080
    ssWidth, ssHeight  = 3840, 2160
    aspectRatio        = float64(ssWidth) / float64(ssHeight)
    fov                = math.Pi / 8
    maxIter            = 1000
    power              = 9
    escapeRadius       = 1.6
    supersamplingRatio = 2
)

var wg sync.WaitGroup

type vec3 struct{ x, y, z float64 }

func (v vec3) add(w vec3) vec3    { return vec3{v.x + w.x, v.y + w.y, v.z + w.z} }
func (v vec3) mul(s float64) vec3 { return vec3{v.x * s, v.y * s, v.z * s} }
func (v vec3) length() float64    { return math.Sqrt(v.x*v.x + v.y*v.y + v.z*v.z) }
func (v vec3) normalize() vec3    { return v.mul(1 / v.length()) }

func mandelbulb(p vec3) float64 {
    z, r, theta, phi := p, 0.0, 0.0, 0.0
    for i := 0; i < maxIter; i++ {
        r = z.length()
        if r > escapeRadius {
            break
        }
        theta, phi = math.Acos(z.z/r)*power, math.Atan2(z.y, z.x)*power
        r = math.Pow(r, power)
        z.x = p.x + r*math.Sin(theta)*math.Cos(phi)
        z.y = p.y + r*math.Sin(theta)*math.Sin(phi)
        z.z = p.z + r*math.Cos(theta)
    }
    return r
}

func renderPixel(x, y int) color.Color {
    px := (2*float64(x)/float64(ssWidth) - 1) * aspectRatio * math.Tan(fov/2)
    py := (1 - 2*float64(y)/float64(ssHeight)) * math.Tan(fov/2)
    direction := vec3{px, py, -1}.normalize()
    t := 0.0
    for i := 0; i < maxIter; i++ {
        p := direction.mul(t).add(vec3{0, 0, 5})
        d := mandelbulb(p) - 1
        if d < 0.001 {
            return color.Gray{uint8(255 - t*255/100)}
        }
        t += d
        if t > 100 {
            break
        }
    }
    return color.Black
}

func main() {
    ssImg := image.NewRGBA(image.Rect(0, 0, ssWidth, ssHeight))
    for y := 0; y < ssHeight; y++ {
        wg.Add(1)
        go func(y int) {
            defer wg.Done()
            for x := 0; x < ssWidth; x++ {
                ssImg.Set(x, y, renderPixel(x, y))
            }
        }(y)
    }
    wg.Wait()

    img := image.NewRGBA(image.Rect(0, 0, width, height))
    for y := 0; y < height; y++ {
        for x := 0; x < width; x++ {
            r, g, b, a := 0, 0, 0, 0
            for dy := 0; dy < supersamplingRatio; dy++ {
                for dx := 0; dx < supersamplingRatio; dx++ {
                    c := ssImg.RGBAAt(x*supersamplingRatio+dx, y*supersamplingRatio+dy)
                    r += int(c.R)
                    g += int(c.G)
                    b += int(c.B)
                    a += int(c.A)
                }
            }
            r /= supersamplingRatio * supersamplingRatio
            g /= supersamplingRatio * supersamplingRatio
            b /= supersamplingRatio * supersamplingRatio
            a /= supersamplingRatio * supersamplingRatio
            img.Set(x, y, color.RGBA{uint8(r), uint8(g), uint8(b), uint8(a)})
        }
    }

    file, err := os.Create("mandelbulb.png")
    if err != nil {
        fmt.Println("Error creating file:", err)
        return
    }
    defer file.Close()
    err = png.Encode(file, img)
    if err != nil {
        fmt.Println("Error encoding image:", err)
    }
}

General info

• Author: Alexander F. Rødseth
• Assistant: GPT4
• License: CC0
• Version: 0.0.1