From 08a5d3f67b7d9ec87830ea39c48e570a1f18531f Mon Sep 17 00:00:00 2001
From: gizak <gizak@icloud.com>
Date: Wed, 27 Jan 2016 14:12:43 -0500
Subject: [PATCH] Fix https://github.com/gizak/termui/issues/75

Negative numbers are suppressed as zeros. The height of each data point
is based off zero, so it will be confusing when it comes to negative
numbers. Simply treat negative values data points as zeroes.
---
 sparkline.go | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/sparkline.go b/sparkline.go
index b438941..312ad95 100644
--- a/sparkline.go
+++ b/sparkline.go
@@ -4,9 +4,7 @@
 
 package termui
 
-import "math"
-
-// Sparkline is like: ▅▆▂▂▅▇▂▂▃▆▆▆▅▃
+// Sparkline is like: ▅▆▂▂▅▇▂▂▃▆▆▆▅▃. The data points should be non-negative integers.
 /*
   data := []int{4, 2, 1, 6, 3, 9, 1, 4, 2, 15, 14, 9, 8, 6, 10, 13, 15, 12, 10, 5, 3, 6, 1}
   spl := termui.NewSparkline()
@@ -84,14 +82,18 @@ func (sl *Sparklines) update() {
 	for i := 0; i < sl.displayLines; i++ {
 		data := sl.Lines[i].Data
 
-		max := math.MinInt32
+		max := 0
 		for _, v := range data {
 			if max < v {
 				max = v
 			}
 		}
 		sl.Lines[i].max = max
-		sl.Lines[i].scale = float32(8*sl.Lines[i].Height) / float32(max)
+		if max != 0 {
+			sl.Lines[i].scale = float32(8*sl.Lines[i].Height) / float32(max)
+		} else { // when all negative
+			sl.Lines[i].scale = 0
+		}
 	}
 }
 
@@ -127,7 +129,12 @@ func (sl *Sparklines) Buffer() Buffer {
 		}
 
 		for j, v := range data {
+			// display height of the data point, zero when data is negative
 			h := int(float32(v)*l.scale + 0.5)
+			if v < 0 {
+				h = 0
+			}
+
 			barCnt := h / 8
 			barMod := h % 8
 			for jj := 0; jj < barCnt; jj++ {