Screen redraw optimization

We don't have to clear the screen every time, we only have to make sure
that we erase the rest of the line that used to be on the current line.
We can still optimize a bit more by finding the longest line and drawing
to that length, but using the full width is fine for now.

cmd/micro/micro.go

@@ -169,7 +169,7 @@ func InitScreen() {
 
 // RedrawAll redraws everything -- all the views and the messenger
 func RedrawAll() {
-	screen.Clear()
+	messenger.Clear()
 	for _, v := range views {
 		v.Display()
 	}

cmd/micro/view.go

@@ -532,7 +532,6 @@ func (v *View) DisplayView() {
 			}
 		}
 		// Write the line
-		tabchars := 0
 		for colN, ch := range line {
 			var lineStyle tcell.Style
 
@@ -570,17 +569,17 @@ func (v *View) DisplayView() {
 					}
 				}
 				indentChar := []rune(settings["indentchar"].(string))
-				screen.SetContent(x-v.leftCol+tabchars, lineN, indentChar[0], nil, lineIndentStyle)
+				screen.SetContent(x-v.leftCol, lineN, indentChar[0], nil, lineIndentStyle)
 				tabSize := int(settings["tabsize"].(float64))
 				for i := 0; i < tabSize-1; i++ {
-					tabchars++
-					if x-v.leftCol+tabchars >= v.lineNumOffset {
-						screen.SetContent(x-v.leftCol+tabchars, lineN, ' ', nil, lineStyle)
+					x++
+					if x-v.leftCol >= v.lineNumOffset {
+						screen.SetContent(x-v.leftCol, lineN, ' ', nil, lineStyle)
 					}
 				}
 			} else {
-				if x-v.leftCol+tabchars >= v.lineNumOffset {
-					screen.SetContent(x-v.leftCol+tabchars, lineN, ch, nil, lineStyle)
+				if x-v.leftCol >= v.lineNumOffset {
+					screen.SetContent(x-v.leftCol, lineN, ch, nil, lineStyle)
 				}
 			}
 			charNum++
@@ -599,10 +598,14 @@ func (v *View) DisplayView() {
 			if style, ok := colorscheme["selection"]; ok {
 				selectStyle = style
 			}
-			screen.SetContent(x-v.leftCol+tabchars, lineN, ' ', nil, selectStyle)
+			screen.SetContent(x-v.leftCol, lineN, ' ', nil, selectStyle)
 		}
 
 		charNum++
+
+		for i := 0; i < v.width-x; i++ {
+			screen.SetContent(x+i, lineN, ' ', nil, defStyle)
+		}
 	}
 }