Make sixel output flicker free

app.go

@@ -435,6 +435,9 @@ func (app *app) loop() {
 			if err == nil {
 				if r.path == curr.path {
 					app.ui.regPrev = r
+					if gOpts.sixel {
+						app.ui.sxScreen.forceClear = true
+					}
 				}
 			}
 

eval.go

@@ -91,9 +91,6 @@ func (e *setExpr) eval(app *app, args []string) {
 			if app.nav.height != app.ui.wins[0].h {
 				app.nav.height = app.ui.wins[0].h
 				clear(app.nav.regCache)
-				if gOpts.sixel {
-					app.ui.sxScreen.lastFile = ""
-				}
 			}
 			app.ui.loadFile(app, true)
 		}
@@ -157,6 +154,9 @@ func (e *setExpr) eval(app *app, args []string) {
 			err = errors.New("preview: 'ratios' should consist of at least two numbers before enabling 'preview'")
 		}
 		if err == nil {
+			if gOpts.sixel {
+				app.ui.sxScreen.forceClear = true
+			}
 			gOpts.preview = preview
 			app.ui.loadFile(app, true)
 		}
@@ -174,6 +174,9 @@ func (e *setExpr) eval(app *app, args []string) {
 		err = applyBoolOpt(&gOpts.showbinds, e)
 	case "sixel", "nosixel", "sixel!":
 		err = applyBoolOpt(&gOpts.sixel, e)
+		clear(app.nav.regCache)
+		app.ui.sxScreen.forceClear = true
+		app.ui.loadFile(app, true)
 	case "smartcase", "nosmartcase", "smartcase!":
 		err = applyBoolOpt(&gOpts.smartcase, e)
 		if err == nil {
@@ -350,7 +353,6 @@ func (e *setExpr) eval(app *app, args []string) {
 		app.ui.wins = getWins(app.ui.screen)
 		if gOpts.sixel {
 			clear(app.nav.regCache)
-			app.ui.sxScreen.lastFile = ""
 		}
 		app.ui.loadFile(app, true)
 	case "scrolloff":
@@ -1433,7 +1435,7 @@ func (e *callExpr) eval(app *app, args []string) {
 		}
 		if gOpts.sixel {
 			clear(app.nav.regCache)
-			app.ui.sxScreen.lastFile = ""
+			app.ui.sxScreen.forceClear = true
 		}
 		for _, dir := range app.nav.dirs {
 			dir.boundPos(app.nav.height)

misc.go

@@ -325,8 +325,9 @@ func getFileExtension(file fs.FileInfo) string {
 }
 
 var (
-	reModKey   = regexp.MustCompile(`<(c|s|a)-(.+)>`)
-	reRulerSub = regexp.MustCompile(`%[apmcsfithd]|%\{[^}]+\}`)
+	reModKey    = regexp.MustCompile(`<(c|s|a)-(.+)>`)
+	reRulerSub  = regexp.MustCompile(`%[apmcsfithd]|%\{[^}]+\}`)
+	reSixelSize = regexp.MustCompile(`"1;1;(\d+);(\d+)`)
 )
 
 var (

sixel.go

@@ -1,69 +1,73 @@
 package main
 
 import (
-	"fmt"
+	"log"
 	"os"
-	"strings"
+	"strconv"
 
 	"github.com/gdamore/tcell/v2"
 )
 
-const (
-	gSixelBegin = "\033P"
-
-	// The filler character should be:
-	// - rarely used: the filler is used to trick tcell into redrawing, if the
-	//   filler character appears in the user's preview, that cell might not
-	//   be cleaned up properly
-	// - ideally renders as empty space: the filler alternates between bold
-	//   and regular, using a non-space would look weird to the user.
-	gSixelFiller = '\u2000'
-)
+const gSixelBegin = "\033P"
 
 type sixelScreen struct {
-	xprev, yprev int
-	sixel        *string
-	altFill      bool
-	lastFile     string // TODO maybe use hash of sixels instead to flip altFill
+	lastFile   string
+	lastWin    win
+	forceClear bool
 }
 
-func (sxs *sixelScreen) fillerStyle(filePath string) tcell.Style {
-	if sxs.lastFile != filePath {
-		sxs.altFill = !sxs.altFill
+func (sxs *sixelScreen) clearSixel(win *win, screen tcell.Screen, filePath string) {
+	if sxs.lastFile != "" && (filePath != sxs.lastFile || *win != sxs.lastWin || sxs.forceClear) {
+		screen.LockRegion(sxs.lastWin.x, sxs.lastWin.y, sxs.lastWin.w, sxs.lastWin.h, false)
 	}
+}
 
-	if sxs.altFill {
-		return tcell.StyleDefault.Bold(true)
+func (sxs *sixelScreen) printSixel(win *win, screen tcell.Screen, reg *reg) {
+	if reg.path == sxs.lastFile && *win == sxs.lastWin && !sxs.forceClear {
+		return
 	}
-	return tcell.StyleDefault
-}
 
-func (sxs *sixelScreen) showSixels() {
-	if sxs.sixel == nil {
+	if reg.sixel == nil {
+		sxs.lastFile = ""
 		return
 	}
 
-	// XXX: workaround for bug where quitting lf might leave the terminal in bold
-	fmt.Fprint(os.Stderr, "\033[0m")
+	ti, err := tcell.LookupTerminfo(os.Getenv("TERM"))
+	if err != nil {
+		log.Printf("sixel: failed to look up term into %s", err)
+		return
+	}
 
-	fmt.Fprint(os.Stderr, "\0337")                              // Save cursor position
-	fmt.Fprintf(os.Stderr, "\033[%d;%dH", sxs.yprev, sxs.xprev) // Move cursor to position
-	fmt.Fprint(os.Stderr, *sxs.sixel)                           //
-	fmt.Fprint(os.Stderr, "\0338")                              // Restore cursor position
-}
+	tty, ok := screen.Tty()
+	if !ok {
+		log.Printf("sixel: failed to get tty")
+		return
+	}
 
-func (sxs *sixelScreen) printSixel(win *win, screen tcell.Screen, reg *reg) {
-	if reg.sixel == nil {
+	ws, err := tty.WindowSize()
+	if err != nil {
+		log.Printf("sixel: failed to get window size %s", err)
+		return
+	}
+	cw, ch := ws.CellDimensions()
+	if cw <= 0 || ch <= 0 {
+		log.Printf("sixel: cell dimensions should not be 0")
 		return
 	}
 
-	// HACK: fillers are used to control when tcell redraws the region where a sixel image is drawn.
-	// alternating between bold and regular is to clear the image before drawing a new one.
-	st := sxs.fillerStyle(reg.path)
-	for y := range win.h {
-		st = win.print(screen, 0, y, st, strings.Repeat(string(gSixelFiller), win.w))
+	matches := reSixelSize.FindStringSubmatch(*reg.sixel)
+	if matches == nil {
+		log.Printf("sixel: failed to get image size")
+		return
 	}
+	iw, _ := strconv.Atoi(matches[1])
+	ih, _ := strconv.Atoi(matches[2])
+
+	screen.LockRegion(win.x, win.y, iw/cw, ih/ch, true)
+	ti.TPuts(tty, ti.TGoto(win.x, win.y))
+	ti.TPuts(tty, *reg.sixel)
 
-	sxs.xprev, sxs.yprev = win.x+1, win.y+1
-	sxs.sixel = reg.sixel
+	sxs.lastFile = reg.path
+	sxs.lastWin = *win
+	sxs.forceClear = false
 }

ui.go

@@ -1020,7 +1020,6 @@ func (ui *ui) draw(nav *nav) {
 	context := dirContext{selections: nav.selections, saves: nav.saves, tags: nav.tags}
 
 	ui.screen.Clear()
-	ui.sxScreen.sixel = nil
 
 	ui.drawPromptLine(nav)
 
@@ -1058,14 +1057,15 @@ func (ui *ui) draw(nav *nav) {
 		ui.screen.ShowCursor(ui.msgWin.x+runeSliceWidth(prefix)+runeSliceWidth(left), ui.msgWin.y)
 	}
 
-	if gOpts.preview {
-		curr, err := nav.currFile()
-		if err == nil {
-			preview := ui.wins[len(ui.wins)-1]
-
+	curr, err := nav.currFile()
+	if err == nil {
+		preview := ui.wins[len(ui.wins)-1]
+		ui.sxScreen.clearSixel(preview, ui.screen, curr.path)
+		if gOpts.preview {
 			if curr.Mode().IsRegular() || (curr.IsDir() && gOpts.dirpreviews) {
 				preview.printReg(ui.screen, ui.regPrev, nav.previewLoading, &ui.sxScreen)
 			} else if curr.IsDir() {
+				ui.sxScreen.lastFile = ""
 				preview.printDir(ui, ui.dirPrev, &context,
 					&dirStyle{colors: ui.styles, icons: ui.icons, role: Preview})
 			}
@@ -1097,10 +1097,6 @@ func (ui *ui) draw(nav *nav) {
 	}
 
 	ui.screen.Show()
-	if ui.menu == "" && ui.cmdPrefix == "" && ui.sxScreen.sixel != nil {
-		ui.sxScreen.lastFile = ui.regPrev.path
-		ui.sxScreen.showSixels()
-	}
 }
 
 func findBinds(keys map[string]expr, prefix string) (binds map[string]expr, ok bool) {
@@ -1522,6 +1518,7 @@ func (ui *ui) readExpr() {
 }
 
 func (ui *ui) suspend() error {
+	ui.sxScreen.forceClear = true
 	return ui.screen.Suspend()
 }