Minor cleanup changes

These include some minor changes that were originally in the v0.4.0 branch, but can be provided without any impact in functionality.  Backporting to keep the API change PR as clean as possible.

axis.go

@@ -68,10 +68,7 @@ func (a *axisPainter) Render() (Box, error) {
 		return BoxZero, nil
 	}
 	top := a.p
-	theme := opt.Theme
-	if theme == nil {
-		theme = top.theme
-	}
+	theme := getPreferredTheme(opt.Theme, top.theme)
 
 	strokeWidth := opt.StrokeWidth
 	if strokeWidth == 0 {
@@ -155,6 +152,7 @@ func (a *axisPainter) Render() (Box, error) {
 	case PositionTop:
 		labelPaddingTop = 0
 		x1 = p.Width()
+		// TODO - should this reference opt.FontStyle or fontStyle with defaults set
 		y0 = labelMargin + int(opt.FontStyle.FontSize)
 		ticksPaddingTop = int(opt.FontStyle.FontSize)
 		y1 = y0

bar_chart.go

@@ -135,8 +135,7 @@ func (b *barChart) render(result *defaultRenderResult, seriesList SeriesList) (B
 			}
 			// generate marker point by hand
 			points[j] = Point{
-				// centered position
-				X: x + barWidth>>1,
+				X: x + (barWidth >> 1), // centered position
 				Y: top,
 			}
 			// return if the label does not need to be displayed

chart_option.go

@@ -8,16 +8,16 @@ import (
 )
 
 type ChartOption struct {
-	// OutputFormat specifies the output type of chart, "svg" or "png", default value is "png"
+	// OutputFormat specifies the output type of chart, "svg" or "png", default value is "png".
 	OutputFormat string
 	// Width is the width of chart, default width is 600.
 	Width int
-	// Height is the height of chart, default height is 400
+	// Height is the height of chart, default height is 400.
 	Height int
 	// Theme specifies the colors used for the chart. Built in themes can be loaded using GetTheme with
 	// "light", "dark", "vivid-light", "vivid-dark", "ant" or "grafana".
 	Theme ColorPalette
-	// Padding specifies the padding for chart, default padding is [20, 10, 10, 10]
+	// Padding specifies the padding for chart, default padding is [20, 10, 10, 10].
 	Padding Box
 	// XAxis are options for the x-axis.
 	XAxis XAxisOption
@@ -33,7 +33,7 @@ type ChartOption struct {
 	Box Box
 	// SeriesList provides the data series.
 	SeriesList SeriesList
-	// RadarIndicators are radar indicator list for radar charts
+	// RadarIndicators are radar indicator list for radar charts.
 	RadarIndicators []RadarIndicator
 	// SymbolShow set this to *false or *true (using False() or True()) to force if the symbols should be shown or hidden.
 	SymbolShow *bool
@@ -50,7 +50,6 @@ type ChartOption struct {
 	// Children are child charts to render together.
 	Children []ChartOption
 	parent   *Painter
-	// TODO - review how this is set on other Option structs
 	// ValueFormatter to format numeric values into labels.
 	ValueFormatter ValueFormatter
 }

echarts.go

@@ -482,17 +482,17 @@ func renderEcharts(options, outputType string) ([]byte, error) {
 	}
 	opt := o.ToOption()
 	opt.OutputFormat = outputType
-	if d, err := Render(opt); err != nil {
+	if p, err := Render(opt); err != nil {
 		return nil, err
 	} else {
-		return d.Bytes()
+		return p.Bytes()
 	}
 }
 
 func RenderEChartsToPNG(options string) ([]byte, error) {
-	return renderEcharts(options, "png")
+	return renderEcharts(options, ChartOutputPNG)
 }
 
 func RenderEChartsToSVG(options string) ([]byte, error) {
-	return renderEcharts(options, "svg")
+	return renderEcharts(options, ChartOutputSVG)
 }

painter.go

@@ -9,31 +9,32 @@ import (
 	"github.com/go-analyze/charts/chartdraw"
 )
 
+// ValueFormatter defines a function that can be used to format numeric values.
 type ValueFormatter func(float64) string
 
 var defaultValueFormatter = func(val float64) string {
 	return FormatValueHumanizeShort(val, 2, false)
 }
 
+// Painter is the primary struct for drawing charts/graphs.
 type Painter struct {
 	render         chartdraw.Renderer
 	box            Box
-	parent         *Painter
 	style          chartdraw.Style
 	theme          ColorPalette
 	font           *truetype.Font
 	outputFormat   string
 	valueFormatter ValueFormatter
 }
 
+// PainterOptions contains parameters for creating a new Painter.
 type PainterOptions struct {
-	// OutputFormat specifies the output type, "svg" or "png", default value is "png"
+	// OutputFormat specifies the output type, "svg" or "png", default is "png".
 	OutputFormat string
 	// Width is the width of the draw painter.
 	Width int
 	// Height is the height of the draw painter.
 	Height int
-	// TODO - is this the best place for font configuration?
 	// Font is the font used for rendering text.
 	Font *truetype.Font
 }
@@ -87,7 +88,7 @@ func PainterPaddingOption(padding Box) PainterOption {
 	}
 }
 
-// PainterBoxOption sets the box of draw painter
+// PainterBoxOption sets a specific box for the Painter to draw within.
 func PainterBoxOption(box Box) PainterOption {
 	return func(p *Painter) {
 		if box.IsZero() {
@@ -114,7 +115,8 @@ func PainterStyleOption(style chartdraw.Style) PainterOption {
 	}
 }
 
-// PainterThemeOption sets the theme of draw painter
+// PainterThemeOption sets a color palette theme default for the Painter.
+// This theme is used if the specific chart options don't have a theme set.
 func PainterThemeOption(theme ColorPalette) PainterOption {
 	return func(p *Painter) {
 		if theme == nil {
@@ -184,13 +186,13 @@ func (p *Painter) setOptions(opts ...PainterOption) {
 
 func (p *Painter) Child(opt ...PainterOption) *Painter {
 	child := &Painter{
-		valueFormatter: p.valueFormatter,
 		render:         p.render,
 		box:            p.box.Clone(),
-		parent:         p,
 		style:          p.style,
 		theme:          p.theme,
 		font:           p.font,
+		outputFormat:   p.outputFormat,
+		valueFormatter: p.valueFormatter,
 	}
 	child.setOptions(opt...)
 	return child
@@ -412,14 +414,17 @@ func (p *Painter) Fill() *Painter {
 	return p
 }
 
+// Width returns the drawable width of the painter's box.
 func (p *Painter) Width() int {
 	return p.box.Width()
 }
 
+// Height returns the drawable height of the painter's box.
 func (p *Painter) Height() int {
 	return p.box.Height()
 }
 
+// MeasureText will provide the rendered size of the text for the provided font style.
 func (p *Painter) MeasureText(text string) Box {
 	return p.render.MeasureText(text)
 }
@@ -439,6 +444,9 @@ func (p *Painter) MeasureTextMaxWidthHeight(textList []string) (int, int) {
 	return maxWidth, maxHeight
 }
 
+// LineStroke draws a line in the graph from point to point with the specified stroke color/width.
+// Points with values of math.MaxInt32 will be skipped, resulting in a gap.
+// Single or isolated points will result in just a dot being drawn at the point.
 func (p *Painter) LineStroke(points []Point) *Painter {
 	var valid []Point
 	for _, pt := range points {
@@ -457,6 +465,8 @@ func (p *Painter) LineStroke(points []Point) *Painter {
 	return p.Stroke()
 }
 
+// drawStraightPath draws a simple (non-curved) path for the given points.
+// If dotForSinglePoint is true, single points are drawn as 2px radius dots.
 func (p *Painter) drawStraightPath(points []Point, dotForSinglePoint bool) {
 	pointCount := len(points)
 	if pointCount == 0 {
@@ -576,6 +586,8 @@ func (p *Painter) SetBackground(width, height int, color Color, inside ...bool)
 	p.FillStroke()
 	return p
 }
+
+// MarkLine draws a horizontal line with a small circle and arrow at the right.
 func (p *Painter) MarkLine(x, y, width int) *Painter {
 	arrowWidth := 16
 	arrowHeight := 10
@@ -590,6 +602,7 @@ func (p *Painter) MarkLine(x, y, width int) *Painter {
 	return p
 }
 
+// Polygon draws a polygon with the specified center, radius, and number of sides.
 func (p *Painter) Polygon(center Point, radius float64, sides int) *Painter {
 	points := getPolygonPoints(center, radius, sides)
 	for i, item := range points {

util.go

@@ -7,8 +7,6 @@ import (
 	"strings"
 
 	"github.com/dustin/go-humanize"
-
-	"github.com/go-analyze/charts/chartdraw"
 )
 
 // True returns a pointer to a true bool, useful for configuration.
@@ -113,18 +111,6 @@ func sumInt(values []int) int {
 	return sum
 }
 
-// measureTextMaxWidthHeight returns maxWidth and maxHeight of text list
-func measureTextMaxWidthHeight(textList []string, p *Painter) (int, int) {
-	maxWidth := 0
-	maxHeight := 0
-	for _, text := range textList {
-		box := p.MeasureText(text)
-		maxWidth = chartdraw.MaxInt(maxWidth, box.Width())
-		maxHeight = chartdraw.MaxInt(maxHeight, box.Height())
-	}
-	return maxWidth, maxHeight
-}
-
 func reverseStringSlice(stringList []string) {
 	for i, j := 0, len(stringList)-1; i < j; i, j = i+1, j-1 {
 		stringList[i], stringList[j] = stringList[j], stringList[i]

util_test.go

@@ -5,9 +5,6 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-
-	"github.com/go-analyze/charts/chartdraw"
 )
 
 func TestGetDefaultInt(t *testing.T) {
@@ -126,53 +123,15 @@ func TestGetRadius(t *testing.T) {
 	assert.Equal(t, 40.0, getRadius(100, ""))
 }
 
-func TestMeasureTextMaxWidthHeight(t *testing.T) {
-	t.Parallel()
-
-	p, err := NewPainter(PainterOptions{
-		Width:  400,
-		Height: 300,
-	})
-	require.NoError(t, err)
-	style := FontStyle{
-		FontSize: 10,
-	}
-	p.SetStyle(chartdraw.Style{FontStyle: style})
-
-	maxWidth, maxHeight := measureTextMaxWidthHeight([]string{
-		"Mon",
-		"Tue",
-		"Wed",
-		"Thu",
-		"Fri",
-		"Sat",
-		"Sun",
-	}, p)
-	assert.Equal(t, 31, maxWidth)
-	assert.Equal(t, 12, maxHeight)
-}
-
 func TestReverseSlice(t *testing.T) {
 	t.Parallel()
 
 	arr := []string{
-		"Mon",
-		"Tue",
-		"Wed",
-		"Thu",
-		"Fri",
-		"Sat",
-		"Sun",
+		"Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun",
 	}
 	reverseStringSlice(arr)
 	assert.Equal(t, []string{
-		"Sun",
-		"Sat",
-		"Fri",
-		"Thu",
-		"Wed",
-		"Tue",
-		"Mon",
+		"Sun", "Sat", "Fri", "Thu", "Wed", "Tue", "Mon",
 	}, arr)
 
 	numbers := []int{1, 3, 5, 7, 9}