package main

import (
	"image"
	"image/color"
)

func HexToRGBA(hexcolor int) color.RGBA {
	return color.RGBA{
		R: uint8(hexcolor >> 0x10 & 0xff),
		G: uint8(hexcolor >> 0x08 & 0xff),
		B: uint8(hexcolor >> 0x00 & 0xff),
		A: 0xff,
	}
}

// performs linear gradient fill on target image for the background from top to bottom colors
func FillGradient(target *image.RGBA, width int, height int, top, bottom color.RGBA) {

	for y := 0; y < height; y++ {

		//the percent of our transition informs our blending
		percentIn := float64(y) / float64(height)

		//compute top and bottom blend values as factor of percentage
		pTopR := float64(top.R) * (1 - percentIn)
		pTopG := float64(top.G) * (1 - percentIn)
		pTopB := float64(top.B) * (1 - percentIn)

		pBottomR := float64(bottom.R) * (percentIn)
		pBottomG := float64(bottom.G) * (percentIn)
		pBottomB := float64(bottom.B) * (percentIn)

		//perform blending on per pixel row basis
		for x := 0; x < width; x++ {
			pixelIndex := 4 * (width*y + x)
			target.Pix[pixelIndex] = uint8(pTopR + pBottomR)
			target.Pix[pixelIndex+1] = uint8(pTopG + pBottomG)
			target.Pix[pixelIndex+2] = uint8(pTopB + pBottomB)
			target.Pix[pixelIndex+3] = 0xff
		}
	}
}