Significant Painter API and SVG rendering changes

Changes put together because both required significant changes to the SVG validation in tests.  These changes were carefully examined to make sure there were no negative visual issues.

**Painter API changes**:
The Painter API can be confusing, with some functions depending on the state of the painter.
This changes the Painter API (internal and external) so that style attributes (ie FillColor, StrokeColor, StrokeWidth, etc) are not stateful. Instead the relevant style values are accepted as arguments to the draw action.

This creates an easier to use API.  It also addresses a complexity if multiple Child painters are used together with different drawing state.

Additionally the Painter configuration has changed.  A default theme and default font is still available to set in the Painter, however the `ValueFormatter` was removed.  Instead this config field only exists in charts options which make use of a set formatter.

Test SVG's resulted from two primary aspects of this change:
  * Measuring text not representing the actual text size due to the font style not set correctly in the Painter
  * A fill style attribute being specified when it has no effect (since style was set due to prior operations)

In general the exposed functions were general examined to ensure all exposed functions are both useful, and easy to use.  This resulted in a number of argument changes, which should be detailed in the go docs.

**vector_renderer (SVG) improvements**:

This change minimizes and simplifies the SVG output through the following:
  * If stroke width is zero, or the color is transparent only `stroke:none` will be set, instead of the prior `stroke-width:0;stroke:none` value
  * Colors will be specified by name if possible, otherwise an RGB or RGBA string will still be used
  * If the text or path is empty, nothing will be inserted into the svg.

These three changes reduce the SVG size.  Specifying the color names could potentially allow color shade changes using CSS.

As a bonus, additional colors are now specified in the `drawing` package.

----

SVG changes are always painful, these were careful evaluated to ensure this is an improvement in both the Painter functionality and SVG results.

Author: jentfoo

axis.go

@@ -3,8 +3,6 @@ package charts
 import (
 	"math"
 	"strings"
-
-	"github.com/go-analyze/charts/chartdraw"
 )
 
 type axisPainter struct {
@@ -97,23 +95,7 @@ func (a *axisPainter) Render() (Box, error) {
 	tickLength := getDefaultInt(opt.TickLength, 5)
 	labelMargin := getDefaultInt(opt.LabelMargin, 5)
 
-	style := chartdraw.Style{
-		StrokeColor: theme.GetAxisStrokeColor(),
-		StrokeWidth: strokeWidth,
-		FontStyle:   fontStyle,
-	}
-	top.SetDrawingStyle(style)
-	top.OverrideFontStyle(style.FontStyle)
-
-	isTextRotation := opt.TextRotation != 0
-
-	if isTextRotation {
-		top.setTextRotation(opt.TextRotation)
-	}
-	textMaxWidth, textMaxHeight := top.measureTextMaxWidthHeight(opt.Data)
-	if isTextRotation {
-		top.clearTextRotation()
-	}
+	textMaxWidth, textMaxHeight := top.measureTextMaxWidthHeight(opt.Data, fontStyle, opt.TextRotation)
 
 	width := 0
 	height := 0
@@ -227,22 +209,25 @@ func (a *axisPainter) Render() (Box, error) {
 	}
 
 	if strokeWidth > 0 {
+		strokeColor := theme.GetAxisStrokeColor()
 		p.Child(PainterPaddingOption(Box{
 			Top:   ticksPaddingTop,
 			Left:  ticksPaddingLeft,
 			IsSet: true,
 		})).ticks(ticksOption{
-			labelCount: labelCount,
-			tickCount:  tickCount,
-			tickSpaces: tickSpaces,
-			length:     tickLength,
-			vertical:   isVertical,
-			firstIndex: opt.DataStartIndex,
+			labelCount:  labelCount,
+			tickCount:   tickCount,
+			tickSpaces:  tickSpaces,
+			length:      tickLength,
+			vertical:    isVertical,
+			firstIndex:  opt.DataStartIndex,
+			strokeWidth: strokeWidth,
+			strokeColor: strokeColor,
 		})
 		p.LineStroke([]Point{
 			{X: x0, Y: y0},
 			{X: x1, Y: y1},
-		})
+		}, strokeColor, strokeWidth)
 	}
 
 	p.Child(PainterPaddingOption(Box{
@@ -254,6 +239,7 @@ func (a *axisPainter) Render() (Box, error) {
 		firstIndex:     opt.DataStartIndex,
 		align:          textAlign,
 		textList:       opt.Data,
+		fontStyle:      fontStyle,
 		vertical:       isVertical,
 		labelCount:     labelCount,
 		tickCount:      tickCount,
@@ -264,9 +250,6 @@ func (a *axisPainter) Render() (Box, error) {
 	})
 
 	if opt.SplitLineShow { // show auxiliary lines
-		style.StrokeColor = theme.GetAxisSplitLineColor()
-		style.StrokeWidth = 1
-		top.OverrideDrawingStyle(style)
 		if isVertical {
 			x0 := p.Width()
 			x1 := top.Width()
@@ -280,7 +263,7 @@ func (a *axisPainter) Render() (Box, error) {
 				top.LineStroke([]Point{
 					{X: x0, Y: y},
 					{X: x1, Y: y},
-				})
+				}, theme.GetAxisSplitLineColor(), 1)
 			}
 		} else {
 			y0 := p.Height() - defaultXAxisHeight
@@ -293,7 +276,7 @@ func (a *axisPainter) Render() (Box, error) {
 				top.LineStroke([]Point{
 					{X: x, Y: y0},
 					{X: x, Y: y1},
-				})
+				}, theme.GetAxisSplitLineColor(), 1)
 			}
 		}
 	}

axis_test.go

@@ -5,8 +5,6 @@ import (
 	"math"
 
 	"github.com/golang/freetype/truetype"
-
-	"github.com/go-analyze/charts/chartdraw"
 )
 
 type barChart struct {
@@ -43,14 +41,17 @@ type BarChartOption struct {
 	BarWidth int
 	// RoundedBarCaps set to `true` to produce a bar graph where the bars have rounded tops.
 	RoundedBarCaps *bool
+	// ValueFormatter defines how float values should be rendered to strings, notably for numeric axis labels.
+	ValueFormatter ValueFormatter
 }
 
 func (b *barChart) render(result *defaultRenderResult, seriesList SeriesList) (Box, error) {
 	p := b.p
 	opt := b.opt
 	seriesPainter := result.seriesPainter
 
-	xRange := newRange(b.p, seriesPainter.Width(), len(opt.XAxis.Data), 0.0, 0.0, 0.0, 0.0)
+	xRange := newRange(b.p, opt.ValueFormatter,
+		seriesPainter.Width(), len(opt.XAxis.Data), 0.0, 0.0, 0.0, 0.0)
 	x0, x1 := xRange.GetRange(0)
 	width := int(x1 - x0)
 	// margin between each block
@@ -108,28 +109,25 @@ func (b *barChart) render(result *defaultRenderResult, seriesList SeriesList) (B
 			}
 
 			h := yRange.getHeight(item)
-			fillColor := seriesColor
 			top := barMaxHeight - h
 
-			seriesPainter.OverrideDrawingStyle(chartdraw.Style{
-				FillColor: fillColor,
-			})
 			if flagIs(true, opt.RoundedBarCaps) {
 				seriesPainter.roundedRect(Box{
 					Top:    top,
 					Left:   x,
 					Right:  x + barWidth,
 					Bottom: barMaxHeight - 1,
 					IsSet:  true,
-				}, barWidth, true, false)
+				}, barWidth, true, false,
+					seriesColor, seriesColor, 0.0)
 			} else {
 				seriesPainter.filledRect(Box{
 					Top:    top,
 					Left:   x,
 					Right:  x + barWidth,
 					Bottom: barMaxHeight - 1,
 					IsSet:  true,
-				})
+				}, seriesColor, seriesColor, 0.0)
 			}
 			// generate marker point by hand
 			points[j] = Point{
@@ -147,7 +145,7 @@ func (b *barChart) render(result *defaultRenderResult, seriesList SeriesList) (B
 				y = barMaxHeight
 				radians = -math.Pi / 2
 				if fontStyle.FontColor.IsZero() {
-					if isLightColor(fillColor) {
+					if isLightColor(seriesColor) {
 						fontStyle.FontColor = defaultLightFontColor
 					} else {
 						fontStyle.FontColor = defaultDarkFontColor
@@ -196,13 +194,14 @@ 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,
-		yAxis:      opt.YAxis,
-		title:      opt.Title,
-		legend:     opt.Legend,
+		theme:          opt.Theme,
+		padding:        opt.Padding,
+		seriesList:     opt.SeriesList,
+		xAxis:          opt.XAxis,
+		yAxis:          opt.YAxis,
+		title:          opt.Title,
+		legend:         opt.Legend,
+		valueFormatter: opt.ValueFormatter,
 	})
 	if err != nil {
 		return BoxZero, err

bar_chart.go

@@ -12,36 +12,71 @@ import (
 var (
 	// ColorTransparent is a fully transparent color.
 	ColorTransparent = Color{R: 255, G: 255, B: 255, A: 0}
-	// ColorWhite is white.
+	// ColorWhite is R: 255, G: 255, B: 255.
 	ColorWhite = Color{R: 255, G: 255, B: 255, A: 255}
-	// ColorBlack is black.
+	// ColorBlack is R: 0, G: 0, B: 0.
 	ColorBlack = Color{R: 0, G: 0, B: 0, A: 255}
-	// ColorRed is red.
+	// ColorGray is R: 128, G: 128, B: 128,
+	ColorGray = Color{R: 128, G: 128, B: 128, A: 255}
+	// ColorRed is R: 255, G: 0, B: 0.
 	ColorRed = Color{R: 255, G: 0, B: 0, A: 255}
-	// ColorGreen is green.
+	// ColorGreen is R: 0, G: 128, B: 0.
 	ColorGreen = Color{R: 0, G: 128, B: 0, A: 255}
-	// ColorBlue is blue.
+	// ColorBlue is R: 0, G: 0, B: 255.
 	ColorBlue = Color{R: 0, G: 0, B: 255, A: 255}
-	// ColorSilver is a known color.
+	// ColorSilver is R: 192, G: 192, B: 192.
 	ColorSilver = Color{R: 192, G: 192, B: 192, A: 255}
-	// ColorMaroon is a known color.
+	// ColorMaroon is R: 128, G: 0, B: 0.
 	ColorMaroon = Color{R: 128, G: 0, B: 0, A: 255}
-	// ColorPurple is a known color.
+	// ColorPurple is R: 128, G: 0, B: 128.
 	ColorPurple = Color{R: 128, G: 0, B: 128, A: 255}
-	// ColorFuchsia is a known color.
+	// ColorFuchsia is R: 255, G: 0, B: 255.
 	ColorFuchsia = Color{R: 255, G: 0, B: 255, A: 255}
-	// ColorLime is a known color.
+	// ColorLime is R: 0, G: 255, B: 0.
 	ColorLime = Color{R: 0, G: 255, B: 0, A: 255}
-	// ColorOlive is a known color.
+	// ColorOlive is R: 128, G: 128, B: 0.
 	ColorOlive = Color{R: 128, G: 128, B: 0, A: 255}
-	// ColorYellow is a known color.
+	// ColorYellow is R: 255, G: 255, B: 0.
 	ColorYellow = Color{R: 255, G: 255, B: 0, A: 255}
-	// ColorNavy is a known color.
+	// ColorNavy is R: 0, G: 0, B: 128.
 	ColorNavy = Color{R: 0, G: 0, B: 128, A: 255}
-	// ColorTeal is a known color.
+	// ColorTeal is R: 0, G: 128, B: 128.
 	ColorTeal = Color{R: 0, G: 128, B: 128, A: 255}
-	// ColorAqua is a known color.
+	// ColorAqua is R: 0, G: 255, B: 255.
 	ColorAqua = Color{R: 0, G: 255, B: 255, A: 255}
+
+	// select extended colors
+
+	// ColorAzure is R: 240, G: 255, B: 255.
+	ColorAzure = Color{R: 240, G: 255, B: 255, A: 255}
+	// ColorBeige is R: 245, G: 245, B: 220.
+	ColorBeige = Color{R: 245, G: 245, B: 220, A: 255}
+	// ColorBrown is R: 165, G: 42, B: 42.
+	ColorBrown = Color{R: 165, G: 42, B: 42, A: 255}
+	// ColorChocolate is R: 210, G: 105, B: 30.
+	ColorChocolate = Color{R: 210, G: 105, B: 30, A: 255}
+	// ColorCoral is R: 255, G: 127, B: 80.
+	ColorCoral = Color{R: 255, G: 127, B: 80, A: 255}
+	// ColorGold is R: 255, G: 215, B: 0.
+	ColorGold = Color{R: 255, G: 215, B: 0, A: 255}
+	// ColorIndigo is R: 75, G: 0, B: 130.
+	ColorIndigo = Color{R: 75, G: 0, B: 130, A: 255}
+	// ColorIvory is R: 255, G: 255, B: 250.
+	ColorIvory = Color{R: 255, G: 255, B: 250, A: 255}
+	// ColorOrange is R: 255, G: 165, B: 0.
+	ColorOrange = Color{R: 255, G: 165, B: 0, A: 255}
+	// ColorPink is R: 255, G: 192, B: 203.
+	ColorPink = Color{R: 255, G: 192, B: 203, A: 255}
+	// ColorPlum is R: 221, G: 160, B: 221.
+	ColorPlum = Color{R: 221, G: 160, B: 221, A: 255}
+	// ColorSalmon is R: 250, G: 128, B: 114.
+	ColorSalmon = Color{R: 250, G: 128, B: 114, A: 255}
+	// ColorTan is R: 210, G: 180, B: 140.
+	ColorTan = Color{R: 210, G: 180, B: 140, A: 255}
+	// ColorTurquoise is R: 64, G: 224, B: 208.
+	ColorTurquoise = Color{R: 64, G: 224, B: 208, A: 255}
+	// ColorViolet is R: 238, G: 130, B: 238.
+	ColorViolet = Color{R: 238, G: 130, B: 238, A: 255}
 )
 
 // ParseColor parses a color from a string.
@@ -129,6 +164,8 @@ func ColorFromKnown(known string) Color {
 		return ColorWhite
 	case "black":
 		return ColorBlack
+	case "grey", "gray":
+		return ColorGray
 	case "red":
 		return ColorRed
 	case "blue":
@@ -153,8 +190,38 @@ func ColorFromKnown(known string) Color {
 		return ColorNavy
 	case "teal":
 		return ColorTeal
-	case "aqua":
+	case "cyan", "aqua":
 		return ColorAqua
+	case "azure":
+		return ColorAzure
+	case "beige":
+		return ColorBeige
+	case "brown":
+		return ColorBrown
+	case "chocolate":
+		return ColorChocolate
+	case "coral":
+		return ColorCoral
+	case "gold":
+		return ColorGold
+	case "indigo":
+		return ColorIndigo
+	case "ivory":
+		return ColorIvory
+	case "orange":
+		return ColorOrange
+	case "pink":
+		return ColorPink
+	case "plum":
+		return ColorPlum
+	case "salmon":
+		return ColorSalmon
+	case "tan":
+		return ColorTan
+	case "turquoise":
+		return ColorTurquoise
+	case "violet":
+		return ColorViolet
 	default:
 		return Color{}
 	}
@@ -235,6 +302,53 @@ func (c Color) AverageWith(other Color) Color {
 
 // String returns a css string representation of the color.
 func (c Color) String() string {
+	switch c {
+	case ColorWhite:
+		return "white"
+	case ColorBlack:
+		return "black"
+	case ColorRed:
+		return "red"
+	case ColorBlue:
+		return "blue"
+	case ColorGreen:
+		return "green"
+	case ColorSilver:
+		return "silver"
+	case ColorMaroon:
+		return "maroon"
+	case ColorPurple:
+		return "purple"
+	case ColorFuchsia:
+		return "fuchsia"
+	case ColorLime:
+		return "lime"
+	case ColorOlive:
+		return "olive"
+	case ColorYellow:
+		return "yellow"
+	case ColorNavy:
+		return "navy"
+	case ColorTeal:
+		return "teal"
+	case ColorAqua:
+		return "aqua"
+	default:
+		if c.A == 255 {
+			return c.StringRGB()
+		} else {
+			return c.StringRGBA()
+		}
+	}
+}
+
+// StringRGB returns a css RGB string representation of the color.
+func (c Color) StringRGB() string {
+	return fmt.Sprintf("rgb(%v,%v,%v)", c.R, c.G, c.B)
+}
+
+// StringRGBA returns a css RGBA string representation of the color.
+func (c Color) StringRGBA() string {
 	fa := float64(c.A) / float64(255)
 	return fmt.Sprintf("rgba(%v,%v,%v,%.1f)", c.R, c.G, c.B, fa)
 }

bar_chart_test.go

@@ -150,6 +150,9 @@ func (rr *rasterRenderer) SetFontColor(c drawing.Color) {
 
 // Text implements the interface method.
 func (rr *rasterRenderer) Text(body string, x, y int) {
+	if body == "" {
+		return
+	}
 	xf, yf := rr.getCoords(x, y)
 	rr.gc.SetFont(rr.s.Font)
 	rr.gc.SetFontSize(rr.s.FontSize)