demos: add sixel demo

Add a demo of sixel drawing

_demos/sixel.go

@@ -0,0 +1,183 @@
+//go:build ignore
+// +build ignore
+
+// Copyright 2023 The TCell Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use file except in compliance with the License.
+// You may obtain a copy of the license at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// sixel displays a sixel and demonstrates how to use direct drawing
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"image"
+	"image/png"
+	"log"
+	"math"
+	"os"
+
+	"github.com/gdamore/tcell/v2"
+	"github.com/gdamore/tcell/v2/encoding"
+
+	"github.com/mattn/go-runewidth"
+	"github.com/mattn/go-sixel"
+)
+
+type imageData struct {
+	width  int // width in pixels
+	height int // height in pixels
+	data   *bytes.Buffer
+}
+
+func emitStr(s tcell.Screen, x, y int, style tcell.Style, str string) {
+	for _, c := range str {
+		var comb []rune
+		w := runewidth.RuneWidth(c)
+		if w == 0 {
+			comb = []rune{c}
+			c = ' '
+			w = 1
+		}
+		s.SetContent(x, y, c, comb, style)
+		x += w
+	}
+}
+
+func displayHelloWorld(s tcell.Screen) {
+	w, h := s.Size()
+	s.Clear()
+	style := tcell.StyleDefault.Foreground(tcell.ColorCadetBlue.TrueColor()).Background(tcell.ColorWhite)
+	emitStr(s, w/2-7, h/2, style, "Hello, World!")
+	emitStr(s, w/2-9, h/2+1, tcell.StyleDefault, "Press ESC to exit.")
+	emitStr(s, w/2-18, h/2+2, tcell.StyleDefault, "Press Enter to toggle sixel lock.")
+	s.Show()
+}
+
+func displaySixel(s tcell.Screen, img *imageData, lock bool) {
+	tty, ok := s.Tty()
+	if !ok {
+		s.Fini()
+		log.Fatal("not a terminal")
+	}
+	ws, err := tty.WindowSize()
+	if err != nil {
+		s.Fini()
+		log.Fatal(err)
+	}
+	// Get the dimensions of a single cell
+	cw, ch := ws.CellDimensions()
+	if cw == 0 || ch == 0 {
+		s.Fini()
+		log.Fatal("terminal does not support sixel graphics")
+		return
+	}
+
+	// Calculate the image dimensions in cells. We round up to prevent
+	// drawing on a partially filled cell
+	sixelWidth := int(math.Ceil(float64(img.width) / float64(cw)))
+	sixelHeight := int(math.Ceil(float64(img.height) / float64(ch)))
+
+	sixelX := ws.Width/2 - (sixelWidth / 2) // Center the image horizontally
+	sixelY := ws.Height/2 - sixelHeight - 2
+	if sixelY < 0 {
+		sixelY = 0
+	}
+	// Lock the region where we will draw the sixel, this prevents tcell
+	// from drawing over this area
+	s.LockRegion(sixelX, sixelY, sixelWidth, sixelHeight, lock)
+
+	// Get the terminfo for our current terminal
+	ti, err := tcell.LookupTerminfo(os.Getenv("TERM"))
+	if err != nil {
+		s.Fini()
+		log.Fatal(err)
+	}
+
+	emitStr(s, sixelX, sixelY, tcell.StyleDefault, "This text is behind")
+	emitStr(s, sixelX, sixelY+1, tcell.StyleDefault, "     the sixel")
+
+	// Move the cursor to our draw position
+	ti.TPuts(tty, ti.TGoto(sixelX, sixelY))
+	// Draw the sixel data
+	ti.TPuts(tty, img.data.String())
+
+	s.Show()
+}
+
+func loadImage(path string) (image.Image, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	return png.Decode(f)
+}
+
+func main() {
+	encoding.Register()
+
+	s, e := tcell.NewScreen()
+	if e != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", e)
+		os.Exit(1)
+	}
+	if e := s.Init(); e != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", e)
+		os.Exit(1)
+	}
+
+	defStyle := tcell.StyleDefault.
+		Background(tcell.ColorBlack).
+		Foreground(tcell.ColorWhite)
+	s.SetStyle(defStyle)
+
+	raw, err := loadImage("./logos/tcell.png")
+	if err != nil {
+		s.Fini()
+		log.Println("couldn't load image. try running from the root directory")
+		log.Fatalf("        go run ./_demos/sixel.go")
+	}
+
+	img := &imageData{
+		width:  raw.Bounds().Dx(),
+		height: raw.Bounds().Dy(),
+		data:   bytes.NewBuffer(nil),
+	}
+	enc := sixel.NewEncoder(img.data)
+	if err := enc.Encode(raw); err != nil {
+		s.Fini()
+		log.Fatal(err)
+	}
+
+	lock := true
+	displayHelloWorld(s)
+	displaySixel(s, img, lock)
+
+	for {
+		switch ev := s.PollEvent().(type) {
+		case *tcell.EventResize:
+			s.Sync()
+			displayHelloWorld(s)
+			displaySixel(s, img, lock)
+		case *tcell.EventKey:
+			if ev.Key() == tcell.KeyEscape {
+				s.Fini()
+				os.Exit(0)
+			}
+			if ev.Key() == tcell.KeyEnter {
+				lock = !lock
+				displaySixel(s, img, lock)
+			}
+		}
+	}
+}