Creates a Plan 9 Palette as a 2D image using the gg library

plan9palette.go

import (
	"github.com/fogleman/gg"
	"image/color/palette"
	"strconv"
	"image/color"
)

func main() {
	const numSquaresPerRow = 16.
	const numSquaresPerColumn = numSquaresPerRow
	const squareSideLength = 64.
	dc := gg.NewContext(numSquaresPerRow*squareSideLength, numSquaresPerColumn*squareSideLength)
	growingOffset := 0
	for i := 0; i < numSquaresPerColumn; i++ {
		if i%4 != 0 {
			growingOffset++
		}
		for j := 0; j < numSquaresPerRow; j++ {
			plan9Color := palette.Plan9[i*numSquaresPerColumn+j].(color.RGBA)
			r, g, b := plan9Color.R, plan9Color.G, plan9Color.B
			oppositeOfPlan9Color := color.RGBA{uint8(0xFF - r), uint8(0xFF - g), uint8(0xFF - b), 0xFF}
			dc.SetColor(plan9Color)
			drawI, drawJ := float64(i), float64(j-growingOffset)
			if drawJ < 0 {
				drawJ = float64(numSquaresPerColumn + drawJ)
			}
			dc.DrawRectangle(drawI*squareSideLength, drawJ*squareSideLength, squareSideLength, squareSideLength)
			dc.Fill()
			dc.SetColor(oppositeOfPlan9Color)
			dc.DrawString(strconv.Itoa(i*numSquaresPerColumn+j), drawI*squareSideLength+squareSideLength/16, drawJ*squareSideLength + squareSideLength)
			dc.Fill()
		}

	}
	savePNG()
}

func savePNG() {
	dc.SavePNG("Plan9_Palette.png")
}