fire.go

// http://fabiensanglard.net/doom_fire_psx/

package fire

import (
	"image"
	"image/color"
	"math/rand"
)

type Fire struct {
	*image.Paletted
}

func New(w, h int) *Fire {
	r := image.Rect(0, 0, w, h)
	img := image.NewPaletted(r, palette)
	b := r.Bounds().Max
	for x := 0; x < b.X; x++ {
		img.SetColorIndex(x, b.Y-1, uint8(len(palette)-1))
	}
	return &Fire{Paletted: img}
}

func (f *Fire) Next() {
	b := f.Bounds().Max
	for x := 0; x < b.X; x++ {
		for y := b.Y - 1; y > 0; y-- {
			z := rand.Intn(3) - 1 // -1, 0, 1
			n := f.ColorIndexAt(x, y)
			if n > 0 && z == 0 {
				n-- // next color
			}
			f.SetColorIndex(x+z, y-1, n)
		}
	}
}

var palette = color.Palette{
	color.RGBA{0x07, 0x07, 0x07, 0xff},
	color.RGBA{0x1f, 0x07, 0x07, 0xff},
	color.RGBA{0x2f, 0x0f, 0x07, 0xff},
	color.RGBA{0x47, 0x0f, 0x07, 0xff},
	color.RGBA{0x57, 0x17, 0x07, 0xff},
	color.RGBA{0x67, 0x1f, 0x07, 0xff},
	color.RGBA{0x77, 0x1f, 0x07, 0xff},
	color.RGBA{0x8f, 0x27, 0x07, 0xff},
	color.RGBA{0x9f, 0x2f, 0x07, 0xff},
	color.RGBA{0xaf, 0x3f, 0x07, 0xff},
	color.RGBA{0xbf, 0x47, 0x07, 0xff},
	color.RGBA{0xc7, 0x47, 0x07, 0xff},
	color.RGBA{0xdf, 0x4f, 0x07, 0xff},
	color.RGBA{0xdf, 0x57, 0x07, 0xff},
	color.RGBA{0xdf, 0x57, 0x07, 0xff},
	color.RGBA{0xd7, 0x5f, 0x07, 0xff},
	color.RGBA{0xd7, 0x67, 0x0f, 0xff},
	color.RGBA{0xcf, 0x6f, 0x0f, 0xff},
	color.RGBA{0xcf, 0x77, 0x0f, 0xff},
	color.RGBA{0xcf, 0x7f, 0x0f, 0xff},
	color.RGBA{0xcf, 0x87, 0x17, 0xff},
	color.RGBA{0xc7, 0x87, 0x17, 0xff},
	color.RGBA{0xc7, 0x8f, 0x17, 0xff},
	color.RGBA{0xc7, 0x97, 0x1f, 0xff},
	color.RGBA{0xbf, 0x9f, 0x1f, 0xff},
	color.RGBA{0xbf, 0x9f, 0x1f, 0xff},
	color.RGBA{0xbf, 0xa7, 0x27, 0xff},
	color.RGBA{0xbf, 0xa7, 0x27, 0xff},
	color.RGBA{0xbf, 0xaf, 0x2f, 0xff},
	color.RGBA{0xb7, 0xaf, 0x2f, 0xff},
	color.RGBA{0xb7, 0xb7, 0x2f, 0xff},
	color.RGBA{0xb7, 0xb7, 0x37, 0xff},
	color.RGBA{0xcf, 0xcf, 0x6f, 0xff},
	color.RGBA{0xdf, 0xdf, 0x9f, 0xff},
	color.RGBA{0xef, 0xef, 0xc7, 0xff},
	color.RGBA{0xff, 0xff, 0xff, 0xff},
}