Building a chessboard image in go

chessboard.go

package main

import (
	"image"
	"image/color"
	"image/jpeg"
	"log"
	"os"
)

func main() {

	m := image.NewRGBA(image.Rect(0, 0, 240, 240))

	white := color.RGBA{uint8(255), uint8(255), 255, 255}
	black := color.RGBA{uint8(0), uint8(0), 0, 255}

	drawGrid(m, black, white)

	if img, err := os.Create("chessboard.jpg"); err != nil {
		log.Println("unable to create img.jpg: %v", err)
	} else {
		jpeg.Encode(img, m, nil)
		defer img.Close()
	}
}

func drawGrid(m *image.RGBA, color1, color2 color.RGBA) {
	size := m.Bounds().Size()
	quad := size.X / 6
	for x := 0; x < size.X; x++ {
		val := (x / quad) % 2
		for y := 0; y < size.Y; y++ {
			val2 := (y / quad) % 2
			if (val+val2)%2 == 0 {
				m.Set(x, y, color1)
			} else {
				m.Set(x, y, color2)
			}
		}
	}
}

I think you could remove the first and second time you use modulo and just use the third.

func drawGrid(m *image.RGBA, color1, color2 color.RGBA) {
    size := m.Bounds().Size()
    quad := size.X / 6
    for x := 0; x < size.X; x++ {
        val := x / quad
        for y := 0; y < size.Y; y++ {
            val2 := y / quad
            if (val+val2)%2 == 0 {
                m.Set(x, y, color1)
            } else {
                m.Set(x, y, color2)
            }
        }
    }
}

also, if your colors are stored in an array, you could rewrite the last if and just call

  m.Set(x,y, colors[ (val+val2)%2 ])