A command-line program to generate a dancing gopher GIF

signdance.go

# Copyright 2019 Google LLC
# SPDX-License-Identifier: Apache-2.0
package main

import (
	"fmt"
	"image"
	"image/color"
	"image/draw"
	"image/gif"
	"os"

	"golang.org/x/image/font"
	"golang.org/x/image/font/basicfont"
	"golang.org/x/image/math/fixed"
)

const sourceGifFile = "./gopher-dance-long-3x-sign.gif"
const destGifFile = "./result.gif"

func main() {
	fin, err := os.Open(sourceGifFile)
	check(err)
	defer fin.Close()
	g, err := gif.DecodeAll(fin)
	check(err)
	fmt.Println(len(g.Image), "frames")

	newLightColor := color.RGBA{255, 200, 200, 255}
	newDimmedColor := color.RGBA{230, 175, 175, 255}

	textColor := color.RGBA{240, 240, 240, 255}

	for i, img := range g.Image {
		modify(i, img, newLightColor, newDimmedColor, "foobar", textColor)
	}

	fout, err := os.OpenFile(destGifFile, os.O_RDWR|os.O_CREATE, 0777)
	err = gif.EncodeAll(fout, g)
	fout.Close()
	check(err)
	fmt.Println("Done.")
}

func modify(i int, img *image.Paletted, newLightColor, newDimmedColor color.Color, message string, textColor color.Color) {
	dx, dy := 25, 35

	for j, c := range img.Palette {
		if c == originalLightColor {
			// Main light blue
			img.Palette[j] = newLightColor
		} else if c == originalDimmedColor {
			// Secondary dimmed blue
			img.Palette[j] = newDimmedColor
		}
	}
	addLabel(img, x[23-i]+dx, y[23-i]+dy, message, textColor)

}

func addLabel(img draw.Image, x, y int, label string, col color.Color) {
	point := fixed.Point26_6{fixed.Int26_6(x * 64), fixed.Int26_6(y * 64)}
	face := basicfont.Face7x13
	face.Width = 14
	face.Height = 26

	d := &font.Drawer{
		Dst:  img,
		Src:  image.NewUniform(col),
		Face: face,
		Dot:  point,
	}
	d.DrawString(label)
}

// Hardcoded positions of the sign
var x = []int{45, 72, 76, 70, 43, 14, 18, 27, 48, 76, 78, 73, 44, 14, 11, 25, 46, 76, 82, 74, 42, 14, 11, 27}
var y = []int{101, 116, 117, 90, 99, 100, 114, 100, 96, 114, 117, 91, 97, 99, 105, 93, 96, 110, 117, 90, 97, 97, 109, 98}

var originalLightColor = color.RGBA{0x96, 0xd6, 0xff, 0xff}
var originalDimmedColor = color.RGBA{0x8d, 0xc9, 0xf0, 0xff}

func check(err error) {
	if err != nil {
		panic(err)
	}
}