package main

import (
	"image"
	"image/color"
)

func setAlpha(path string, alpha int) error {
	src, err := decodeImage(path)
	if err != nil {
		return err
	}
	bounds := src.Bounds()
	dst := image.NewNRGBA(bounds)
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			c := color.NRGBAModel.Convert(src.At(x, y)).(color.NRGBA)
			if c.A > 0 {
				c.A = uint8(alpha)
			}
			dst.Set(x, y, c)
		}
	}
	return encodePNG(path, dst)
}