learngo image solution (#79)

gistfile1.go

package main

import (
	"image"
	"tour/pic"
	"image/color"
)

type Image struct{
  w int
  h int
  v uint8
}

func (i Image) ColorModel() color.Model {
  return color.RGBAModel
}

func (i Image) Bounds() image.Rectangle {
  return image.Rect(0, 0, i.w, i.h)
}

func (i Image) At(x, y int) color.Color {
  return color.RGBA{uint8(x^y), uint8(y), i.v, 255}
}

func main() {
	m := Image{
	  w: 400,
	  h: 400,
	  v: 128}
	pic.ShowImage(m)
}