go - Using the Set() method of an image.Image or *image.RGBA -


i doing practice go image package free time summer.

package main  import (      "os"     "image"     "image/png"     "image/color"     "log"     "fmt"     "reflect"  )  func main(){      file , err := os.openfile("c:/sources/go3x3.png", os.o_rdwr, os.filemode(0777))     if err != nil {         log.fatal(err)     }      img , err := png.decode(file)     if err != nil {         log.fatal(err)     }       img.at(0,0).rgba()     fmt.println("type:", reflect.typeof(img))      m := image.newrgba(image.rect(0, 0, 640, 480))     fmt.println("type:", reflect.typeof(m))     m.set(5, 5, color.rgba{255, 0, 0, 255})     img.set(0, 0, color.rgba{136, 0, 21, 255}) }

the problem here when run img.set commented out result 

type: *image.rgba type: *image.rgba

but when it's uncommented error saying 

img.set undefined (type image.image has no field or method set)

i'm assuming i'm using reflect wrong, i'm still grasping whole interface , type definitions in go.

to expand on anonymous' answer:

png.decode may create 1 of several different underlying image types (*image.gray, *image.rgba, *image.paletted, *image.nrgba, etc). returns whatever image created image.image interface provides read access data.

however, (most?) of actual image types returns implement set method simple write access. way can safely test , use method via existing draw.image interface image/draw package. it's this:

// image/draw: // image image.image set method change single pixel. type image interface {         image.image         set(x, y int, c color.color) }

so like:

func drawablepngimage(r io.reader) (draw.image, error) {     img, err := png.decode(r)     if err != nil {         return nil, err     }     dimg, ok := img.(draw.image)     if !ok {         return nil, fmt.errorf("%t not drawable image type", img)     }     return dimg, nil }

playground (shows example calling image.image methods set).


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