Minor refactoring tcell library from tui.go to tcell.go

To prevent including tcell library in non-windows builds.

src/tui/tcell.go

@@ -120,8 +120,11 @@ func (a Attr) Merge(b Attr) Attr {
 	return a | b
 }
 
+// handle the following as private members of FullscreenRenderer instance
+// they are declared here to prevent introducing tcell library in non-windows builds
 var (
-	_screen tcell.Screen
+	_screen          tcell.Screen
+	_prevMouseButton tcell.ButtonMask
 )
 
 func (r *FullscreenRenderer) initScreen() {
@@ -193,8 +196,8 @@ func (r *FullscreenRenderer) GetChar() Event {
 		mod := ev.Modifiers() != 0
 
 		// since we dont have mouse down events (unlike LightRenderer), we need to track state in prevButton
-		prevButton, button := r.prevMouseButton, ev.Buttons()
-		r.prevMouseButton = button
+		prevButton, button := _prevMouseButton, ev.Buttons()
+		_prevMouseButton = button
 		drag := prevButton == button
 
 		switch {

src/tui/tui.go

@@ -5,8 +5,6 @@ import (
 	"os"
 	"strconv"
 	"time"
-
-	"github.com/gdamore/tcell"
 )
 
 // Types of user action
@@ -399,22 +397,20 @@ type Window interface {
 }
 
 type FullscreenRenderer struct {
-	theme           *ColorTheme
-	mouse           bool
-	forceBlack      bool
-	prevDownTime    time.Time
-	prevMouseButton tcell.ButtonMask
-	clickY          []int
+	theme        *ColorTheme
+	mouse        bool
+	forceBlack   bool
+	prevDownTime time.Time
+	clickY       []int
 }
 
 func NewFullscreenRenderer(theme *ColorTheme, forceBlack bool, mouse bool) Renderer {
 	r := &FullscreenRenderer{
-		theme:           theme,
-		mouse:           mouse,
-		forceBlack:      forceBlack,
-		prevDownTime:    time.Unix(0, 0),
-		prevMouseButton: tcell.ButtonNone,
-		clickY:          []int{}}
+		theme:        theme,
+		mouse:        mouse,
+		forceBlack:   forceBlack,
+		prevDownTime: time.Unix(0, 0),
+		clickY:       []int{}}
 	return r
 }