fix flicker issue in main view

go.mod

@@ -20,7 +20,7 @@ require (
 	github.com/imdario/mergo v0.3.11
 	github.com/integrii/flaggy v1.4.0
 	github.com/jesseduffield/go-git/v5 v5.1.2-0.20201006095850-341962be15a4
-	github.com/jesseduffield/gocui v0.3.1-0.20210405093708-e79dab8f7772
+	github.com/jesseduffield/gocui v0.3.1-0.20210406065942-1b0c68414064
 	github.com/jesseduffield/termbox-go v0.0.0-20200823212418-a2289ed6aafe // indirect
 	github.com/jesseduffield/yaml v2.1.0+incompatible
 	github.com/kardianos/osext v0.0.0-20190222173326-2bc1f35cddc0

go.sum

@@ -102,6 +102,10 @@ github.com/jesseduffield/gocui v0.3.1-0.20210405041826-439abd8b6e07 h1:BymGR28au
 github.com/jesseduffield/gocui v0.3.1-0.20210405041826-439abd8b6e07/go.mod h1:QWq79xplEoyhQO+dgpk3sojjTVRKjQklyTlzm5nC5Kg=
 github.com/jesseduffield/gocui v0.3.1-0.20210405093708-e79dab8f7772 h1:dg9krj10Udac4IcvlVCOAPktQkfggkgtqRmbDKk7Pzw=
 github.com/jesseduffield/gocui v0.3.1-0.20210405093708-e79dab8f7772/go.mod h1:QWq79xplEoyhQO+dgpk3sojjTVRKjQklyTlzm5nC5Kg=
+github.com/jesseduffield/gocui v0.3.1-0.20210406065811-95ef6e13779b h1:3+4+muhhikpls5FePXSRNFgcdoPx8dTdqaCy3AqLz98=
+github.com/jesseduffield/gocui v0.3.1-0.20210406065811-95ef6e13779b/go.mod h1:QWq79xplEoyhQO+dgpk3sojjTVRKjQklyTlzm5nC5Kg=
+github.com/jesseduffield/gocui v0.3.1-0.20210406065942-1b0c68414064 h1:Oe+QJuUIOd2TU+A3BW5sT1eXqceoBcOOfyoHlGf7F8Y=
+github.com/jesseduffield/gocui v0.3.1-0.20210406065942-1b0c68414064/go.mod h1:QWq79xplEoyhQO+dgpk3sojjTVRKjQklyTlzm5nC5Kg=
 github.com/jesseduffield/termbox-go v0.0.0-20200823212418-a2289ed6aafe h1:qsVhCf2RFyyKIUe/+gJblbCpXMUki9rZrHuEctg6M/E=
 github.com/jesseduffield/termbox-go v0.0.0-20200823212418-a2289ed6aafe/go.mod h1:anMibpZtqNxjDbxrcDEAwSdaJ37vyUeM1f/M4uekib4=
 github.com/jesseduffield/yaml v2.1.0+incompatible h1:HWQJ1gIv2zHKbDYNp0Jwjlj24K8aqpFHnMCynY1EpmE=

pkg/gui/tasks_adapter.go

@@ -83,13 +83,23 @@ func (gui *Gui) getManager(view *gocui.View) *tasks.ViewBufferManager {
 			gui.Log,
 			view,
 			func() {
-				view.Clear()
+				// we could clear here, but that actually has the effect of causing a flicker
+				// where the view may contain no content momentarily as the gui refreshes.
+				// Instead, we're rewinding the write pointer so that we will just start
+				// overwriting the existing content from the top down. Once we've reached
+				// the end of the content do display, we call view.FlushStaleCells() to
+				// clear out the remaining content from the previous render.
+				view.Rewind()
 			},
 			func() {
 				gui.g.Update(func(*gocui.Gui) error {
 					return nil
 				})
-			})
+			},
+			func() {
+				view.FlushStaleCells()
+			},
+		)
 		gui.viewBufferManagerMap[view.Name()] = manager
 	}
 

pkg/tasks/tasks.go

@@ -33,12 +33,13 @@ type ViewBufferManager struct {
 	readLines    chan int
 
 	// beforeStart is the function that is called before starting a new task
-	beforeStart func()
-	refreshView func()
+	beforeStart     func()
+	refreshView     func()
+	flushStaleCells func()
 }
 
-func NewViewBufferManager(log *logrus.Entry, writer io.Writer, beforeStart func(), refreshView func()) *ViewBufferManager {
-	return &ViewBufferManager{Log: log, writer: writer, beforeStart: beforeStart, refreshView: refreshView, readLines: make(chan int, 1024)}
+func NewViewBufferManager(log *logrus.Entry, writer io.Writer, beforeStart func(), refreshView func(), flushStaleCells func()) *ViewBufferManager {
+	return &ViewBufferManager{Log: log, writer: writer, beforeStart: beforeStart, refreshView: refreshView, flushStaleCells: flushStaleCells, readLines: make(chan int, 1024)}
 }
 
 func (m *ViewBufferManager) ReadLines(n int) {
@@ -75,7 +76,7 @@ func (m *ViewBufferManager) NewCmdTask(r io.Reader, cmd *exec.Cmd, prefix string
 			loaded := false
 
 			go utils.Safe(func() {
-				ticker := time.NewTicker(time.Millisecond * 100)
+				ticker := time.NewTicker(time.Millisecond * 200)
 				defer ticker.Stop()
 				select {
 				case <-ticker.C:
@@ -114,6 +115,9 @@ func (m *ViewBufferManager) NewCmdTask(r io.Reader, cmd *exec.Cmd, prefix string
 						default:
 						}
 						if !ok {
+							// if we're here then there's nothing left to scan from the source
+							// so we're at the EOF and can flush the stale content
+							m.flushStaleCells()
 							m.refreshView()
 							break outer
 						}

vendor/github.com/jesseduffield/gocui/view.go

@@ -518,16 +518,20 @@ func (v *View) writeCells(x, y int, cells []cell) {
 // of functions like fmt.Fprintf, fmt.Fprintln, io.Copy, etc. Clear must
 // be called to clear the view's buffer.
 func (v *View) Write(p []byte) (n int, err error) {
-	v.tainted = true
 	v.writeMutex.Lock()
+	defer v.writeMutex.Unlock()
+
+	v.tainted = true
 	v.makeWriteable(v.wx, v.wy)
 	v.writeRunes(bytes.Runes(p))
-	v.writeMutex.Unlock()
 
 	return len(p), nil
 }
 
 func (v *View) WriteRunes(p []rune) {
+	v.writeMutex.Lock()
+	defer v.writeMutex.Unlock()
+
 	v.tainted = true
 
 	// Fill with empty cells, if writing outside current view buffer
@@ -545,6 +549,8 @@ func (v *View) writeRunes(p []rune) {
 	for _, r := range p {
 		switch r {
 		case '\n':
+			// clear the rest of the line
+			v.lines[v.wy] = v.lines[v.wy][0:v.wx]
 			v.wy++
 			if v.wy >= len(v.lines) {
 				v.lines = append(v.lines, nil)
@@ -642,6 +648,15 @@ func (v *View) Read(p []byte) (n int, err error) {
 
 // Rewind sets read and write pos to (0, 0).
 func (v *View) Rewind() {
+	v.writeMutex.Lock()
+	defer v.writeMutex.Unlock()
+
+	v.rewind()
+}
+
+func (v *View) rewind() {
+	v.ei.reset()
+
 	if err := v.SetReadPos(0, 0); err != nil {
 		// SetReadPos returns error only if x and y are negative
 		// we are passing 0, 0, thus no error should occur.
@@ -832,13 +847,31 @@ func (v *View) realPosition(vx, vy int) (x, y int, err error) {
 // And resets reading and writing offsets.
 func (v *View) Clear() {
 	v.writeMutex.Lock()
-	v.Rewind()
+	defer v.writeMutex.Unlock()
+
+	v.rewind()
 	v.tainted = true
-	v.ei.reset()
 	v.lines = nil
 	v.viewLines = nil
 	v.clearRunes()
-	v.writeMutex.Unlock()
+}
+
+// This is for when we've done a rewind for the sake of avoiding a flicker and
+// we've reached the end of the new content to display: we need to clear the remaining
+// content from the previous round.
+func (v *View) FlushStaleCells() {
+	v.writeMutex.Lock()
+	defer v.writeMutex.Unlock()
+
+	// need to wipe the end of the current line and all following lines
+	if len(v.lines) > 0 && v.wy < len(v.lines) {
+		// why this needs to be +1 but the 0:v.wx part doesn't, I'm not sure
+		v.lines = v.lines[0 : v.wy+1]
+
+		if len(v.lines[v.wy]) > 0 && v.wx < len(v.lines[v.wy]) {
+			v.lines[v.wy] = v.lines[v.wy][0:v.wx]
+		}
+	}
 }
 
 // clearRunes erases all the cells in the view.

vendor/modules.txt

@@ -149,7 +149,7 @@ github.com/jesseduffield/go-git/v5/utils/merkletrie/filesystem
 github.com/jesseduffield/go-git/v5/utils/merkletrie/index
 github.com/jesseduffield/go-git/v5/utils/merkletrie/internal/frame
 github.com/jesseduffield/go-git/v5/utils/merkletrie/noder
-# github.com/jesseduffield/gocui v0.3.1-0.20210405093708-e79dab8f7772
+# github.com/jesseduffield/gocui v0.3.1-0.20210406065942-1b0c68414064
 ## explicit
 github.com/jesseduffield/gocui
 # github.com/jesseduffield/termbox-go v0.0.0-20200823212418-a2289ed6aafe