fix: maintain cursor visibility across altscreen state switch

Based on #462 and #452 by @londek, but fixes maintaining the
current visibility state across altscreen state changes.

This makes the behavior consistent across terminals, some of which
keep separate state for altscreen and regular buffer.

Fixes #190.

screen_test.go

@@ -19,12 +19,12 @@ func TestClearMsg(t *testing.T) {
 		{
 			name:     "altscreen",
 			cmds:     []Cmd{EnterAltScreen, ExitAltScreen},
-			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1H\x1b[?1049lsuccess\r\n\x1b[0D\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l",
+			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1H\x1b[?25l\x1b[?1049l\x1b[?25lsuccess\r\n\x1b[0D\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l",
 		},
 		{
 			name:     "altscreen_autoexit",
 			cmds:     []Cmd{EnterAltScreen},
-			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1Hsuccess\r\n\x1b[2;0H\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l\x1b[?1049l",
+			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1H\x1b[?25lsuccess\r\n\x1b[2;0H\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l\x1b[?1049l\x1b[?25h",
 		},
 		{
 			name:     "mouse_cellmotion",

standard_renderer.go

@@ -38,6 +38,9 @@ type standardRenderer struct {
 	useANSICompressor  bool
 	once               sync.Once
 
+	// cursor visibility state
+	cursorHidden bool
+
 	// essentially whether or not we're using the full size of the terminal
 	altScreenActive bool
 
@@ -299,6 +302,15 @@ func (r *standardRenderer) enterAltScreen() {
 	r.out.ClearScreen()
 	r.out.MoveCursor(1, 1)
 
+	// cmd.exe and other terminals keep separate cursor states for the AltScreen
+	// and the main buffer. We have to explicitly reset the cursor visibility
+	// whenever we enter AltScreen.
+	if r.cursorHidden {
+		r.out.HideCursor()
+	} else {
+		r.out.ShowCursor()
+	}
+
 	r.repaint()
 }
 
@@ -313,20 +325,31 @@ func (r *standardRenderer) exitAltScreen() {
 	r.altScreenActive = false
 	r.out.ExitAltScreen()
 
+	// cmd.exe and other terminals keep separate cursor states for the AltScreen
+	// and the main buffer. We have to explicitly reset the cursor visibility
+	// whenever we exit AltScreen.
+	if r.cursorHidden {
+		r.out.HideCursor()
+	} else {
+		r.out.ShowCursor()
+	}
+
 	r.repaint()
 }
 
 func (r *standardRenderer) showCursor() {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()
 
+	r.cursorHidden = false
 	r.out.ShowCursor()
 }
 
 func (r *standardRenderer) hideCursor() {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()
 
+	r.cursorHidden = true
 	r.out.HideCursor()
 }