fixes #576 Intermittent screen flashes

screen.go

@@ -24,12 +24,13 @@ type Screen interface {
 	// Fini finalizes the screen also releasing resources.
 	Fini()
 
-	// Clear erases the screen.  The contents of any screen buffers
-	// will also be cleared.  This has the logical effect of
-	// filling the screen with spaces, using the global default style.
+	// Clear logically erases the screen.
+	// This is effectively a short-cut for Fill(' ', StyleDefault).
 	Clear()
 
 	// Fill fills the screen with the given character and style.
+	// The effect of filling the screen is not visible until Show
+	// is called (or Sync).
 	Fill(rune, Style)
 
 	// SetCell is an older API, and will be removed.  Please use
@@ -42,7 +43,7 @@ type Screen interface {
 	// and may not actually be what is displayed, but rather are what will
 	// be displayed if Show() or Sync() is called.  The width is the width
 	// in screen cells; most often this will be 1, but some East Asian
-	// characters require two cells.
+	// characters and emoji require two cells.
 	GetContent(x, y int) (primary rune, combining []rune, style Style, width int)
 
 	// SetContent sets the contents of the given cell location.  If
@@ -54,7 +55,7 @@ type Screen interface {
 	//
 	// The results are not displayed until Show() or Sync() is called.
 	//
-	// Note that wide (East Asian full width) runes occupy two cells,
+	// Note that wide (East Asian full width and emoji) runes occupy two cells,
 	// and attempts to place character at next cell to the right will have
 	// undefined effects.  Wide runes that are printed in the
 	// last column will be replaced with a single width space on output.

tscreen.go

@@ -575,18 +575,6 @@ func (t *tScreen) SetStyle(style Style) {
 
 func (t *tScreen) Clear() {
 	t.Fill(' ', t.style)
-	t.Lock()
-	t.clear = true
-	w, h := t.cells.Size()
-	// because we are going to clear (see t.clear) in the next cycle,
-	// let's also unmark the dirty bit so that we don't waste cycles
-	// drawing things that are already dealt with via the clear escape sequence.
-	for row := 0; row < h; row++ {
-		for col := 0; col < w; col++ {
-			t.cells.SetDirty(col, row, false)
-		}
-	}
-	t.Unlock()
 }
 
 func (t *tScreen) Fill(r rune, style Style) {