GOLANG program to create png files

draw.go

package main                                                                                                             
                                                                                                                         
import (                                                                                                                 
    "image"                                                                                                              
    "image/color"                                                                                                        
    "image/png"                                                                                                          
    "os"                                                                                                                 
)                                                                                                                        
                                                                                                                         
const (                                                                                                                  
    size     = 301                                                                                                       
    fileName = "draw.png"                                                                                                
)                                                                                                                        
                                                                                                                         
var palette = []color.Color{                                                                                             
    color.RGBA{0xaf, 0xaf, 0xff, 0xff},                                                                                  
    color.RGBA{0xaf, 0xff, 0xaf, 0xee},                                                                                  
}                                                                                                                        
                                                                                                                         
func main() {                                                                                                            
    rect := image.Rect(0, 0, size, size)                                                                                 
    img := image.NewPaletted(rect, palette)                                                                              
                                                                                                                         
    for x := 0; x < size; x++ {                                                                                          
        for y := 0; y < size; y++ {                                                                                      
            if visible(x, y) {                                                                                           
                img.SetColorIndex(x, y, 1)                                                                               
            }                                                                                                            
        }                                                                                                                
    }                                                                                                                    
                                                                                                                         
    f, err := os.Create(fileName)                                                                                        
    if err != nil {                                                                                                      
        panic(err)                                                                                                       
    }                                                                                                                    
    defer f.Close()                                                                                                      
    png.Encode(f, img)                                                                                                   
}                                                                                                                        
                                                                                                                         
func visible(x int, y int) bool {                                                                                        
    value := x*x + y*y                                                                                                   
    module := value % 10                                                                                                 
                                                                                                                         
    if module == 0 {                                                                                                     
        return true                                                                                                      
    }                                                                                                                    
                                                                                                                         
    return false                                                                                                         
}