add scrollbars

vendor/github.com/jesseduffield/gocui/scrollbar.go

@@ -0,0 +1,33 @@
+package gocui
+
+import "math"
+
+// returns start and height of scrollbar
+// `max` is the maximum possible value of `position`
+func calcScrollbar(listSize int, pageSize int, position int, scrollAreaSize int) (int, int) {
+	height := calcScrollbarHeight(listSize, pageSize, scrollAreaSize)
+	// assume we can't scroll past the last item
+	maxPosition := listSize - pageSize
+	if maxPosition <= 0 {
+		return 0, height
+	}
+	if position == maxPosition {
+		return scrollAreaSize - height, height
+	}
+	// we only want to show the scrollbar at the top or bottom positions if we're at the end. Hence the .Ceil (for moving the scrollbar once we scroll down) and the -1 (for pretending there's a smaller range than we actually have, with the above condition ensuring we snap to the bottom once we're at the end of the list)
+	start := int(math.Ceil(((float64(position) / float64(maxPosition)) * float64(scrollAreaSize-height-1))))
+	return start, height
+}
+
+func calcScrollbarHeight(listSize int, pageSize int, scrollAreaSize int) int {
+	if pageSize >= listSize {
+		return scrollAreaSize
+	}
+	height := int((float64(pageSize) / float64(listSize)) * float64(scrollAreaSize))
+	minHeight := 2
+	if height < minHeight {
+		return minHeight
+	}
+
+	return height
+}