bmp.go

package main

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

        "golang.org/x/image/bmp"
)

func main() {
        f, err := os.Create("out.bmp")
        if err != nil {
                log.Println(err)
                return
        }
        defer f.Close()

        w, h := 800, 480
        im := NewBW(w, h)
        for y := 0; y < h; y++ {
                for x := 0; x < w; x++ {
                        idx := x + y*w
                        im.Buf[idx] = byte((x ^ y) & 1)
                }
        }

        err = bmp.Encode(f, im)
        if err != nil {
                log.Println(err)
                return
        }
}

type Color byte

func (c Color) RGBA() (r, g, b, a uint32) {
        a = 0xffff
        if c != 0 {
                r = 0xffff
                g = 0xffff
                b = 0xffff
        }
        return
}

type BW struct {
        Width, Height int
        Buf           []byte
}

func NewBW(w, h int) *BW {
        return &BW{
                Width:  w,
                Height: h,
                Buf:    make([]byte, w*h),
        }
}

func (im *BW) ColorModel() color.Model {
        return color.Palette([]color.Color{Color(0), Color(1)})
}

func (im *BW) Bounds() image.Rectangle {
        return image.Rectangle{Max: image.Point{X: im.Width, Y: im.Height}}
}

func (im *BW) At(x, y int) color.Color {
        idx := x + y*im.Width
        if idx >= len(im.Buf) {
                return nil
        }
        return Color(im.Buf[idx])
}