Config API updates and improved go docs

These changes are designed to improve consistency and simplicity of chart configuration.

General Changes

* Public config struct fields have had their docs updated and improved.
* `Type` has been renamed to `OutputFormat`, this better describes the format that you want the chart rendered to.
* Heavier theme use - color specifications that were already possible to derive from the theme have been removed, instead the theme is now just always used. As a future change we will allow easier theme modifications to more easily allow one off customization.
* `TrueFlag()` and `FlaseFlag()` have been renamed to just `True()` and `False()`
* `NewFloatPoint(float64)` has been renamed to `FloatPointer`
* Fields with `Option` in their name have had the `Option` removed. This makes names more concise, and for `YAxisOptions` renaming to `YAxis` made it more consistent when compared to `XAxis`.

Axis-Specific Changes

* YAxisOptions field renamed to `YAxis` as mentioned above.
* `FirstAxis` has been renamed to the more descriptive `DataStartIndex`
* `StrokeColor` and `SplitLineColor` has been removed (as mentioned above, theme is now used). You can use `WithAxisColor(Color)` to easily change an existing theme to a different axis color. We plan to improve this API further.
* YAxis `Color` has been renamed to the more descriptive `AxisColor`. Depending on how easy we can make theme adjustments this field may be deprecated. It is preferred to modify the theme using `WithAxisColor(Color)`.

Chart-Specific Changes

* Line charts `Opacity` has been renamed to the more descriptive `FillOpacity` (avoid confusion with other shading opacity)
* For Grid and Table charts `Column` and `Row` were made plural into `Columns` and `Rows`
* For Table charts `Padding` was renamed to the more descriptive `CellPadding` (avoid confusion with chart padding).

alias.go

@@ -17,18 +17,18 @@ type Point struct {
 }
 
 const (
-	ChartTypeLine   = "line"
-	ChartTypeBar    = "bar"
-	ChartTypePie    = "pie"
-	ChartTypeRadar  = "radar"
-	ChartTypeFunnel = "funnel"
-	// horizontal bar
+	ChartTypeLine          = "line"
+	ChartTypeBar           = "bar"
+	ChartTypePie           = "pie"
+	ChartTypeRadar         = "radar"
+	ChartTypeFunnel        = "funnel"
 	ChartTypeHorizontalBar = "horizontalBar"
 )
 
 const (
-	ChartOutputSVG = "svg"
-	ChartOutputPNG = "png"
+	ChartOutputSVG           = "svg"
+	ChartOutputPNG           = "png"
+	chartDefaultOutputFormat = ChartOutputPNG
 )
 
 const (

axis.go

@@ -20,42 +20,38 @@ func NewAxisPainter(p *Painter, opt AxisOption) *axisPainter {
 }
 
 type AxisOption struct {
-	// The theme of chart
+	// Show specifies if the axis should be rendered, set this to *false (through False()) to hide the axis.
+	Show *bool
+	// Theme specifies the colors used for the axis.
 	Theme ColorPalette
-	// Formatter for y axis text value
-	Formatter string
-	// The label of axis
+	// Data provides labels for the axis.
 	Data []string
-	// The boundary gap on both sides of a coordinate axis.
-	// Nil or *true means the center part of two axis ticks
-	BoundaryGap *bool
-	// The flag for show axis, set this to *false will hide axis
-	Show *bool
-	// The position of axis, it can be 'left', 'top', 'right' or 'bottom'
+	// DataStartIndex specifies what index the Data values should start from.
+	DataStartIndex int
+	// Formatter for replacing axis text values.
+	Formatter string
+	// Position describes the position of axis, it can be 'left', 'top', 'right' or 'bottom'.
 	Position string
-	// The line color of axis
-	StrokeColor Color
-	// The line width
+	// BoundaryGap specifies that the chart should have additional space on the left and right, with data points being
+	// centered between two axis ticks.  Enabled by default, specify *false (through False()) to change the spacing.
+	BoundaryGap *bool
+	// StrokeWidth is the axis line width.
 	StrokeWidth float64
-	// The length of the axis tick
+	// TickLength is the length of each axis tick.
 	TickLength int
-	// The first axis
-	FirstAxis int
-	// The margin value of label
+	// LabelMargin specifies the margin value of each label.
 	LabelMargin int
-	// The font size of label
+	// FontSize specifies the font size of each label.
 	FontSize float64
-	// The font of label
+	// Font is the font used to render each label.
 	Font *truetype.Font
-	// The color of label
+	// FontColor is the color used for text rendered.
 	FontColor Color
-	// The flag for show axis split line, set this to true will show axis split line
+	// SplitLineShow, set this to true will show axis split line.
 	SplitLineShow bool
-	// The color of split line
-	SplitLineColor Color
-	// The text rotation of label
+	// TextRotation are the radians for rotating the label.
 	TextRotation float64
-	// The offset of label
+	// LabelOffset is the offset of each label.
 	LabelOffset Box
 	// Unit is a suggestion for how large the axis step is, this is a recommendation only. Larger numbers result in fewer labels.
 	Unit float64
@@ -91,10 +87,6 @@ func (a *axisPainter) Render() (Box, error) {
 	if fontSize == 0 {
 		fontSize = defaultFontSize
 	}
-	strokeColor := opt.StrokeColor
-	if strokeColor.IsZero() {
-		strokeColor = theme.GetAxisStrokeColor()
-	}
 
 	formatter := opt.Formatter
 	if len(formatter) != 0 {
@@ -112,7 +104,7 @@ func (a *axisPainter) Render() (Box, error) {
 	labelMargin := getDefaultInt(opt.LabelMargin, 5)
 
 	style := Style{
-		StrokeColor: strokeColor,
+		StrokeColor: theme.GetAxisStrokeColor(),
 		StrokeWidth: strokeWidth,
 		Font:        font,
 		FontColor:   fontColor,
@@ -235,17 +227,11 @@ func (a *axisPainter) Render() (Box, error) {
 			TickSpaces: tickSpaces,
 			Length:     tickLength,
 			Orient:     orient,
-			First:      opt.FirstAxis,
+			First:      opt.DataStartIndex,
 		})
 		p.LineStroke([]Point{
-			{
-				X: x0,
-				Y: y0,
-			},
-			{
-				X: x1,
-				Y: y1,
-			},
+			{X: x0, Y: y0},
+			{X: x1, Y: y1},
 		})
 	}
 
@@ -254,7 +240,7 @@ func (a *axisPainter) Render() (Box, error) {
 		Top:   labelPaddingTop,
 		Right: labelPaddingRight,
 	})).MultiText(MultiTextOption{
-		First:          opt.FirstAxis,
+		First:          opt.DataStartIndex,
 		Align:          textAlign,
 		TextList:       opt.Data,
 		Orient:         orient,
@@ -266,7 +252,7 @@ func (a *axisPainter) Render() (Box, error) {
 	})
 
 	if opt.SplitLineShow { // show auxiliary lines
-		style.StrokeColor = opt.SplitLineColor
+		style.StrokeColor = theme.GetAxisSplitLineColor()
 		style.StrokeWidth = 1
 		top.OverrideDrawingStyle(style)
 		if isVertical {
@@ -280,14 +266,8 @@ func (a *axisPainter) Render() (Box, error) {
 			yValues = yValues[0 : len(yValues)-1]
 			for _, y := range yValues {
 				top.LineStroke([]Point{
-					{
-						X: x0,
-						Y: y,
-					},
-					{
-						X: x1,
-						Y: y,
-					},
+					{X: x0, Y: y},
+					{X: x1, Y: y},
 				})
 			}
 		} else {
@@ -299,21 +279,12 @@ func (a *axisPainter) Render() (Box, error) {
 					continue
 				}
 				top.LineStroke([]Point{
-					{
-						X: x,
-						Y: y0,
-					},
-					{
-						X: x,
-						Y: y1,
-					},
+					{X: x, Y: y0},
+					{X: x, Y: y1},
 				})
 			}
 		}
 	}
 
-	return Box{
-		Bottom: height,
-		Right:  width,
-	}, nil
+	return Box{Bottom: height, Right: width}, nil
 }

axis_test.go

@@ -28,8 +28,7 @@ func TestAxis(t *testing.T) {
 						"Sat",
 						"Sun",
 					},
-					SplitLineShow:  true,
-					SplitLineColor: drawing.ColorBlack,
+					SplitLineShow: true,
 				}).Render()
 				return p.Bytes()
 			},
@@ -48,7 +47,7 @@ func TestAxis(t *testing.T) {
 						"Sat",
 						"Sun",
 					},
-					BoundaryGap: FalseFlag(),
+					BoundaryGap: False(),
 				}).Render()
 				return p.Bytes()
 			},
@@ -86,10 +85,9 @@ func TestAxis(t *testing.T) {
 						"Sat",
 						"Sun",
 					},
-					Position:       PositionLeft,
-					BoundaryGap:    FalseFlag(),
-					SplitLineShow:  true,
-					SplitLineColor: drawing.ColorBlack,
+					Position:      PositionLeft,
+					BoundaryGap:   False(),
+					SplitLineShow: true,
 				}).Render()
 				return p.Bytes()
 			},
@@ -108,10 +106,9 @@ func TestAxis(t *testing.T) {
 						"Sat",
 						"Sun",
 					},
-					Position:       PositionRight,
-					BoundaryGap:    FalseFlag(),
-					SplitLineShow:  true,
-					SplitLineColor: drawing.ColorBlack,
+					Position:      PositionRight,
+					BoundaryGap:   False(),
+					SplitLineShow: true,
 				}).Render()
 				return p.Bytes()
 			},
@@ -139,13 +136,21 @@ func TestAxis(t *testing.T) {
 		},
 	}
 
+	testThemeName := "axisTestTheme"
+	InstallTheme(testThemeName, ThemeOption{
+		IsDarkMode:         false,
+		AxisStrokeColor:    Color{R: 110, G: 112, B: 121, A: 255},
+		AxisSplitLineColor: drawing.ColorBlack,
+		BackgroundColor:    drawing.ColorWhite,
+		TextColor:          Color{R: 70, G: 70, B: 70, A: 255},
+	})
 	for i, tt := range tests {
 		t.Run(strconv.Itoa(i), func(t *testing.T) {
 			p, err := NewPainter(PainterOptions{
-				Type:   ChartOutputSVG,
-				Width:  600,
-				Height: 400,
-			}, PainterThemeOption(GetTheme(ThemeLight)))
+				OutputFormat: ChartOutputSVG,
+				Width:        600,
+				Height:       400,
+			}, PainterThemeOption(GetTheme(testThemeName)))
 			require.NoError(t, err)
 			data, err := tt.render(p)
 			require.NoError(t, err)

bar_chart.go

@@ -21,22 +21,23 @@ func NewBarChart(p *Painter, opt BarChartOption) *barChart {
 }
 
 type BarChartOption struct {
-	// The theme
+	// Theme specifies the colors used for the bar chart.
 	Theme ColorPalette
-	// The font to use
+	// Padding specifies the padding of bar chart.
+	Padding Box
+	// Font is the font used to render the chart.
 	Font *truetype.Font
-	// The data series list
+	// SeriesList provides the data series.
 	SeriesList SeriesList
-	// The x-axis options
+	// XAxis are options for the x-axis.
 	XAxis XAxisOption
-	// The padding of line chart
-	Padding Box
-	// The y-axis options
-	YAxisOptions []YAxisOption
-	// The option of title
+	// YAxis are options for the y-axis (at most two).
+	YAxis []YAxisOption
+	// Title are options for rendering the title.
 	Title TitleOption
-	// The legend option
-	Legend   LegendOption
+	// Legend are options for the data legend.
+	Legend LegendOption
+	// BarWidth specifies the width of each bar.
 	BarWidth int
 }
 
@@ -78,7 +79,7 @@ func (b *barChart) render(result *defaultRenderResult, seriesList SeriesList) (B
 	}
 	for index := range seriesList {
 		series := seriesList[index]
-		yRange := result.axisRanges[series.AxisIndex]
+		yRange := result.axisRanges[series.YAxisIndex]
 		seriesColor := theme.GetSeriesColor(series.index)
 
 		divideValues := xRange.AutoDivide()
@@ -187,13 +188,13 @@ func (b *barChart) Render() (Box, error) {
 		opt.Theme = getPreferredTheme(p.theme)
 	}
 	renderResult, err := defaultRender(p, defaultRenderOption{
-		Theme:        opt.Theme,
-		Padding:      opt.Padding,
-		SeriesList:   opt.SeriesList,
-		XAxis:        opt.XAxis,
-		YAxisOptions: opt.YAxisOptions,
-		TitleOption:  opt.Title,
-		LegendOption: opt.Legend,
+		Theme:      opt.Theme,
+		Padding:    opt.Padding,
+		SeriesList: opt.SeriesList,
+		XAxis:      opt.XAxis,
+		YAxis:      opt.YAxis,
+		Title:      opt.Title,
+		Legend:     opt.Legend,
 	})
 	if err != nil {
 		return BoxZero, err

bar_chart_test.go

@@ -62,7 +62,7 @@ func makeBasicBarChartOption() BarChartOption {
 			"Nov",
 			"Dec",
 		}),
-		YAxisOptions: NewYAxisOptions([]string{
+		YAxis: NewYAxisOptions([]string{
 			"Rainfall",
 			"Evaporation",
 		}),
@@ -94,9 +94,9 @@ func TestBarChart(t *testing.T) {
 
 	for _, tt := range tests {
 		painterOptions := PainterOptions{
-			Type:   ChartOutputSVG,
-			Width:  600,
-			Height: 400,
+			OutputFormat: ChartOutputSVG,
+			Width:        600,
+			Height:       400,
 		}
 		if tt.defaultTheme {
 			t.Run(tt.name, func(t *testing.T) {