Golang : Set image canvas or background to transparent
Putting this down here for my own future reference. Maybe useful to you too. Anyway, basically what I need is to make an image canvas or background to transparent before drawing over it.
For example, I need to set the foreground color to black and set the background to transparent :
foreGroundColor := image.NewUniform(black)
backGroundColor := image.Transparent
backgroundWidth := 700
backgroundHeight := 50
background = image.NewRGBA(image.Rect(0, 0, backgroundWidth, backgroundHeight))
draw.Draw(background, background.Bounds(), backGroundColor, image.ZP, draw.Src)
// draw something with foreGroundColor.....
alternatively, this method will work as well.
// make every pixel transparent
for y := 0; y < backgroundHeight; y++ {
for x := 0; x < backgroundWidth; x++ {
background.Set(x, y, image.Transparent)
}
}
To test, save the background to a PNG file.
// Save that background image to PNG.
imgFile, err := os.Create("background.png")
if err != nil {
fmt.Println(err)
os.Exit(-1)
}
defer imgFile.Close()
buff := bufio.NewWriter(imgFile)
err = png.Encode(buff, background)
if err != nil {
fmt.Println(err)
os.Exit(-1)
}
err = buff.Flush()
if err != nil {
fmt.Println(err)
os.Exit(-1)
}
fmt.Println("Save to background.png")
Remember...... that JPEG does not support transparency.
Happy coding!
References:
https://www.socketloop.com/references/golang-image-alpha-set-and-setalpha-functions-examples
By Adam Ng
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