Rewrite sixel code to reduce flickering

sixel.go

@@ -15,55 +15,49 @@ const (
 	// - 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.
+	// - ideally renders as empty space
 	gSixelFiller = '\u2000'
 )
 
 type sixelScreen struct {
-	xprev, yprev int
-	sixel        *string
-	altFill      bool
-	lastFile     string // TODO maybe use hash of sixels instead to flip altFill
+	win      *win
+	sixel    *string
+	lastFile string // TODO maybe use hash of sixels instead
 }
 
-func (sxs *sixelScreen) fillerStyle(filePath string) tcell.Style {
-	if sxs.lastFile != filePath {
-		sxs.altFill = !sxs.altFill
-	}
-
-	if sxs.altFill {
-		return tcell.StyleDefault.Bold(true)
-	}
-	return tcell.StyleDefault
-}
-
-func (sxs *sixelScreen) showSixels() {
+func (sxs *sixelScreen) clearSixels(screen tcell.Screen) {
 	if sxs.sixel == nil {
 		return
 	}
 
-	// XXX: workaround for bug where quitting lf might leave the terminal in bold
-	fmt.Fprint(os.Stderr, "\033[0m")
+	filler := strings.Repeat(string(gSixelFiller), sxs.win.w)
+	for y := 0; y < sxs.win.h; y++ {
+		sxs.win.print(screen, 0, y, tcell.StyleDefault, filler)
+	}
+
+	sxs.sixel = nil
+}
 
-	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
+func (sxs *sixelScreen) setSixels(win *win, sixel *string) {
+	sxs.win = win
+	sxs.sixel = sixel
 }
 
-func (sxs *sixelScreen) printSixel(win *win, screen tcell.Screen, reg *reg) {
-	if reg.sixel == nil {
+func (sxs *sixelScreen) showSixels(screen tcell.Screen, path string) {
+	if sxs.sixel == nil {
 		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 := 0; y < win.h; y++ {
-		st = win.print(screen, 0, y, st, strings.Repeat(string(gSixelFiller), win.w))
+	if path != sxs.lastFile {
+		tmp := sxs.sixel
+		sxs.clearSixels(screen)
+		sxs.sixel = tmp
 	}
 
-	sxs.xprev, sxs.yprev = win.x+1, win.y+1
-	sxs.sixel = reg.sixel
+	fmt.Fprint(os.Stderr, "\0337")                                  // Save cursor position
+	fmt.Fprintf(os.Stderr, "\033[%d;%dH", sxs.win.y+1, sxs.win.x+1) // Move cursor to position
+	fmt.Fprint(os.Stderr, *sxs.sixel)                               //
+	fmt.Fprint(os.Stderr, "\0338")                                  // Restore cursor position
+
+	sxs.lastFile = path
 }

ui.go

@@ -267,15 +267,19 @@ func (win *win) printReg(screen tcell.Screen, reg *reg, previewLoading bool, sxs
 		return
 	}
 
+	if reg.sixel != nil {
+		sxs.setSixels(win, reg.sixel)
+	} else {
+		sxs.clearSixels(screen)
+	}
+
 	for i, l := range reg.lines {
 		if i > win.h-1 {
 			break
 		}
 
 		st = win.print(screen, 2, i, st, l)
 	}
-
-	sxs.printSixel(win, screen, reg)
 }
 
 var gThisYear = time.Now().Year()
@@ -1026,14 +1030,7 @@ func (ui *ui) draw(nav *nav) {
 	st := tcell.StyleDefault
 	context := dirContext{selections: nav.selections, saves: nav.saves, tags: nav.tags}
 
-	// XXX: manual clean without flush to avoid flicker on Windows
-	wtot, htot := ui.screen.Size()
-	for i := 0; i < wtot; i++ {
-		for j := 0; j < htot; j++ {
-			ui.screen.SetContent(i, j, ' ', nil, st)
-		}
-	}
-	ui.sxScreen.sixel = nil
+	ui.screen.Clear()
 
 	ui.drawPromptLine(nav)
 
@@ -1077,7 +1074,12 @@ func (ui *ui) draw(nav *nav) {
 		if err == nil {
 			preview := ui.wins[len(ui.wins)-1]
 
+			if ui.menuBuf != nil {
+				ui.sxScreen.clearSixels(ui.screen)
+			}
+
 			if curr.IsDir() {
+				ui.sxScreen.clearSixels(ui.screen)
 				preview.printDir(ui, ui.dirPrev, &context,
 					&dirStyle{colors: ui.styles, icons: ui.icons, role: Preview},
 					nav.previewLoading)
@@ -1112,9 +1114,8 @@ func (ui *ui) draw(nav *nav) {
 	}
 
 	ui.screen.Show()
-	if ui.menuBuf == nil && ui.cmdPrefix == "" && ui.sxScreen.sixel != nil {
-		ui.sxScreen.lastFile = ui.regPrev.path
-		ui.sxScreen.showSixels()
+	if ui.menuBuf == nil && ui.sxScreen.sixel != nil {
+		ui.sxScreen.showSixels(ui.screen, ui.regPrev.path)
 	}
 }