add scroll draw method to canvas

canvas.go

@@ -274,3 +274,55 @@ if you want to hide the caret. Used by controls like EditField
 func (fb *FrameBuffer) SetCursorPos(x, y int) {
 	term.SetCursor(x, y)
 }
+
+/*
+DrawScroll paints a scroll bar inside FrameBuffer.
+x, y - start position.
+w, h - width and height (if h equals 1 then horizontal scroll is drawn
+and vertical otherwise).
+pos - thumb position.
+fgScroll, bgScroll - scroll bar main attributes.
+fgThumb, bgThumb - thumb colors.
+scrollChars  - rune set(by default, in case of is is empty string, the
+rune set equals "░■▲▼")
+*/
+func (fb *FrameBuffer) DrawScroll(x, y, w, h, pos int, fgScroll, bgScroll, fgThumb, bgThumb term.Attribute, scrollChars string) {
+	if w < 1 || h < 1 {
+		return
+	}
+
+	if scrollChars == "" {
+		scrollChars = "░■▲▼"
+	}
+
+	parts := []rune(scrollChars)
+	chLine, chCursor, chUp, chDown := parts[0], parts[1], parts[2], parts[3]
+
+	if h == 1 {
+		fb.PutChar(x, y, chUp, fgScroll, bgScroll)
+		fb.PutChar(x+w-1, y, chDown, fgScroll, bgScroll)
+
+		if w > 2 {
+			for xx := 1; xx < w-1; xx++ {
+				fb.PutChar(x+xx, y, chLine, fgScroll, bgScroll)
+			}
+		}
+
+		if pos != -1 {
+			fb.PutChar(x+pos, y, chCursor, fgThumb, bgThumb)
+		}
+	} else {
+		fb.PutChar(x, y, chUp, fgScroll, bgScroll)
+		fb.PutChar(x, y+h-1, chDown, fgScroll, bgScroll)
+
+		if h > 2 {
+			for yy := 1; yy < h-1; yy++ {
+				fb.PutChar(x, y+yy, chLine, fgScroll, bgScroll)
+			}
+		}
+
+		if pos != -1 {
+			fb.PutChar(x, y+pos, chCursor, fgThumb, bgThumb)
+		}
+	}
+}

interface.go

@@ -49,6 +49,18 @@ type Canvas interface {
 	FillRect(x int, y int, width int, height int, symbol term.Cell)
 	// DrawFrame paints a frame inside Canvas with optional border rune set(by default, in case of border is empty string, the rune set equals "─│┌┐└┘" - single border). The inner area of frame is not filled - in other words it is transparent
 	DrawFrame(x int, y int, width int, height int, fg term.Attribute, bg term.Attribute, border string)
+	/*
+	   DrawScroll paints a scroll bar inside FrameBuffer.
+	   x, y - start position.
+	   w, h - width and height (if h equals 1 then horizontal scroll is drawn
+	   and vertical otherwise).
+	   pos - thumb position.
+	   fgScroll, bgScroll - scroll bar main attributes.
+	   fgThumb, bgThumb - thumb colors.
+	   scrollChars  - rune set(by default, in case of is is empty string, the
+	   rune set equals "░■▲▼")
+	*/
+	DrawScroll(x, y, w, h, pos int, fgScroll, bgScroll, fgThumb, bgThumb term.Attribute, scrollChars string)
 	// SetCursorPos sets text caret position. Used by controls like EditField
 	SetCursorPos(x int, y int)
 }

listbox.go

@@ -68,36 +68,24 @@ func NewListBox(view View, parent Control, width, height int, scale int) *ListBo
 }
 
 func (l *ListBox) redrawScroll(canvas Canvas, tm Theme) {
-	parts := []rune(tm.SysObject(ObjScrollBar))
-
-	chLine, chCursor, chUp, chDown := parts[0], parts[1], parts[2], parts[3]
-
 	fg, bg := RealColor(tm, l.fg, ColorScrollText), RealColor(tm, l.bg, ColorScrollBack)
 	fgThumb, bgThumb := RealColor(tm, l.fg, ColorThumbText), RealColor(tm, l.bg, ColorThumbBack)
 
-	canvas.PutSymbol(l.x+l.width-1, l.y, term.Cell{Ch: chUp, Fg: fg, Bg: bg})
-	canvas.PutSymbol(l.x+l.width-1, l.y+l.height-1, term.Cell{Ch: chDown, Fg: fg, Bg: bg})
-
-	if l.height > 2 {
-		for yy := 1; yy < l.height-1; yy++ {
-			canvas.PutSymbol(l.x+l.width-1, l.y+yy, term.Cell{Ch: chLine, Fg: fg, Bg: bg})
+	pos := -1
+	if l.currSelection != -1 {
+		if len(l.items) > 1 {
+			ydiff := int(float32(l.currSelection) / float32(len(l.items)-1.0) * float32(l.height-3))
+			l.buttonPos = ydiff + 1
+			if l.height == 3 {
+				pos = 1
+			} else {
+				pos = l.buttonPos
+			}
+		} else {
+			pos = 1
 		}
 	}
-
-	if l.currSelection == -1 {
-		return
-	}
-
-	if l.height == 3 || l.currSelection <= 0 {
-		canvas.PutSymbol(l.x+l.width-1, l.y+1, term.Cell{Ch: chCursor, Fg: fgThumb, Bg: bgThumb})
-		return
-	}
-
-	// if l.pressY == -1 {
-	ydiff := int(float32(l.currSelection) / float32(len(l.items)-1.0) * float32(l.height-3))
-	l.buttonPos = ydiff + 1
-	// }
-	canvas.PutSymbol(l.x+l.width-1, l.y+l.buttonPos, term.Cell{Ch: chCursor, Fg: fgThumb, Bg: bgThumb})
+	canvas.DrawScroll(l.x+l.width-1, l.y, 1, l.height, pos, fg, bg, fgThumb, bgThumb, tm.SysObject(ObjScrollBar))
 }
 
 func (l *ListBox) redrawItems(canvas Canvas, tm Theme) {