Add a scroll bar option

The option is `scrollbar` and is off by default. The scroll bar is
not interactive (you can't click and drag it) but this will likely
be fixed in the future.

Ref #869

cmd/micro/micro.go

@@ -476,6 +476,8 @@ func main() {
 		}
 
 		for event != nil {
+			didAction := false
+
 			switch e := event.(type) {
 			case *tcell.EventResize:
 				for _, t := range tabs {
@@ -505,24 +507,36 @@ func main() {
 								}
 							}
 						}
+					} else if e.Buttons() == tcell.WheelUp || e.Buttons() == tcell.WheelDown {
+						var view *View
+						x, y := e.Position()
+						for _, v := range tabs[curTab].views {
+							if x >= v.x && x < v.x+v.Width && y >= v.y && y < v.y+v.Height {
+								view = tabs[curTab].views[v.Num]
+							}
+						}
+						view.HandleEvent(e)
+						didAction = true
 					}
 				}
 			}
 
-			// This function checks the mouse event for the possibility of changing the current tab
-			// If the tab was changed it returns true
-			if TabbarHandleMouseEvent(event) {
-				break
-			}
+			if !didAction {
+				// This function checks the mouse event for the possibility of changing the current tab
+				// If the tab was changed it returns true
+				if TabbarHandleMouseEvent(event) {
+					break
+				}
 
-			if searching {
-				// Since searching is done in real time, we need to redraw every time
-				// there is a new event in the search bar so we need a special function
-				// to run instead of the standard HandleEvent.
-				HandleSearchEvent(event, CurView())
-			} else {
-				// Send it to the view
-				CurView().HandleEvent(event)
+				if searching {
+					// Since searching is done in real time, we need to redraw every time
+					// there is a new event in the search bar so we need a special function
+					// to run instead of the standard HandleEvent.
+					HandleSearchEvent(event, CurView())
+				} else {
+					// Send it to the view
+					CurView().HandleEvent(event)
+				}
 			}
 
 			select {

cmd/micro/scrollbar.go

@@ -0,0 +1,18 @@
+package main
+
+type ScrollBar struct {
+	view *View
+}
+
+func (sb *ScrollBar) Display() {
+	style := defStyle.Reverse(true)
+	screen.SetContent(sb.view.x+sb.view.Width-1, sb.view.y+sb.Pos(), ' ', nil, style)
+}
+
+func (sb *ScrollBar) Pos() int {
+	numlines := sb.view.Buf.NumLines
+	h := sb.view.Height
+	filepercent := float32(sb.view.Topline) / float32(numlines)
+
+	return int(filepercent * float32(h))
+}

cmd/micro/settings.go

@@ -213,6 +213,7 @@ func DefaultGlobalSettings() map[string]interface{} {
 		"savecursor":     false,
 		"savehistory":    true,
 		"saveundo":       false,
+		"scrollbar":      false,
 		"scrollmargin":   float64(3),
 		"scrollspeed":    float64(2),
 		"softwrap":       false,
@@ -248,6 +249,7 @@ func DefaultLocalSettings() map[string]interface{} {
 		"ruler":          true,
 		"savecursor":     false,
 		"saveundo":       false,
+		"scrollbar":      false,
 		"scrollmargin":   float64(3),
 		"scrollspeed":    float64(2),
 		"softwrap":       false,

cmd/micro/view.go

@@ -62,7 +62,7 @@ type View struct {
 	// The buffer
 	Buf *Buffer
 	// The statusline
-	sline Statusline
+	sline *Statusline
 
 	// Since tcell doesn't differentiate between a mouse release event
 	// and a mouse move event with no keys pressed, we need to keep
@@ -92,6 +92,8 @@ type View struct {
 	cellview *CellView
 
 	splitNode *LeafNode
+
+	scrollbar *ScrollBar
 }
 
 // NewView returns a new fullscreen view
@@ -117,7 +119,11 @@ func NewViewWidthHeight(buf *Buffer, w, h int) *View {
 
 	v.messages = make(map[string][]GutterMessage)
 
-	v.sline = Statusline{
+	v.sline = &Statusline{
+		view: v,
+	}
+
+	v.scrollbar = &ScrollBar{
 		view: v,
 	}
 
@@ -1008,6 +1014,11 @@ func (v *View) Display() {
 		screen.HideCursor()
 	}
 	_, screenH := screen.Size()
+
+	if v.Buf.Settings["scrollbar"].(bool) {
+		v.scrollbar.Display()
+	}
+
 	if v.Buf.Settings["statusline"].(bool) {
 		v.sline.Display()
 	} else if (v.y + v.Height) != screenH-1 {

runtime/help/options.md

@@ -146,6 +146,10 @@ Here are the options that you can set:
 
 	default value: `off`
 
+* `scrollbar`: display a scroll bar
+
+    default value: `off`
+
 * `scrollmargin`: amount of lines you would like to see above and below the
    cursor.