From 50605907c761ba72f14f9f666775b394202195c8 Mon Sep 17 00:00:00 2001
From: vicanso <tree.xie@outlook.com>
Date: Thu, 15 Sep 2022 20:09:00 +0800
Subject: [PATCH] feat: support null value for line chart

---
 charts.go                   | 13 +++++++++++++
 examples/line_chart/main.go |  3 ++-
 line_chart.go               |  5 +++++
 painter.go                  |  9 ++++++++-
 series.go                   |  4 ++++
 5 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/charts.go b/charts.go
index 6d5dc56..f7e52e4 100644
--- a/charts.go
+++ b/charts.go
@@ -24,6 +24,7 @@ package charts
 
 import (
 	"errors"
+	"math"
 	"sort"
 
 	"github.com/wcharczuk/go-chart/v2"
@@ -51,6 +52,18 @@ func SetDefaultHeight(height int) {
 	}
 }
 
+var nullValue = math.MaxFloat64
+
+// SetNullValue sets the null value, default is MaxFloat64
+func SetNullValue(v float64) {
+	nullValue = v
+}
+
+// GetNullValue gets the null value
+func GetNullValue() float64 {
+	return nullValue
+}
+
 type Renderer interface {
 	Render() (Box, error)
 }
diff --git a/examples/line_chart/main.go b/examples/line_chart/main.go
index 36eabee..97d5859 100644
--- a/examples/line_chart/main.go
+++ b/examples/line_chart/main.go
@@ -29,7 +29,8 @@ func main() {
 			120,
 			132,
 			101,
-			134,
+			// 134,
+			charts.GetNullValue(),
 			90,
 			230,
 			210,
diff --git a/line_chart.go b/line_chart.go
index 0b44cdf..839aa6f 100644
--- a/line_chart.go
+++ b/line_chart.go
@@ -23,6 +23,8 @@
 package charts
 
 import (
+	"math"
+
 	"github.com/golang/freetype/truetype"
 	"github.com/wcharczuk/go-chart/v2/drawing"
 )
@@ -115,6 +117,9 @@ func (l *lineChart) render(result *defaultRenderResult, seriesList SeriesList) (
 		points := make([]Point, 0)
 		for i, item := range series.Data {
 			h := yRange.getRestHeight(item.Value)
+			if item.Value == nullValue {
+				h = math.MaxInt
+			}
 			p := Point{
 				X: xValues[i],
 				Y: h,
diff --git a/painter.go b/painter.go
index 1a954e2..f172cb3 100644
--- a/painter.go
+++ b/painter.go
@@ -438,11 +438,18 @@ func (p *Painter) MeasureTextMaxWidthHeight(textList []string) (int, int) {
 }
 
 func (p *Painter) LineStroke(points []Point) *Painter {
+	shouldMoveTo := false
 	for index, point := range points {
 		x := point.X
 		y := point.Y
-		if index == 0 {
+		if y == math.MaxInt {
+			p.Stroke()
+			shouldMoveTo = true
+			continue
+		}
+		if shouldMoveTo || index == 0 {
 			p.MoveTo(x, y)
+			shouldMoveTo = false
 		} else {
 			p.LineTo(x, y)
 		}
diff --git a/series.go b/series.go
index ea71869..7bd6834 100644
--- a/series.go
+++ b/series.go
@@ -165,6 +165,10 @@ func (sl SeriesList) GetMaxMin(axisIndex int) (float64, float64) {
 			continue
 		}
 		for _, item := range series.Data {
+			// 如果为空值，忽略
+			if item.Value == nullValue {
+				continue
+			}
 			if item.Value > max {
 				max = item.Value
 			}