Allow solid colored glyphs have a different colored outline

Created by: zaddok

Here is an initial go at a patch that allows solid coloured Glyphs to have an outline.

A keen observer may note that an update to allow a PyramidGlyph to be solid coloured with an outline, is almost the same as if we had allowed TriangleGlyph to have a fill. (ditto for Box/Square, and Circle,Round).

There is probably a case for arguing that we don't need PyramidGlyph and TriangleGlyph as they are both the same except with a different fill or stroke colour, but I don't want such arguments to hold up a useful patch :D Can we patch first and argue how to present the API later?

Where in the past we may have done:

     p, err := plot.New()
     ....
     lpPoints.Shape = draw.CircleGlyph{}
     lpPoints.Color = color.RGBA{R: 255, G: 200, B: 200, A: 255}
     p.Add(lpLine, lpPoints)

We can now do:

     p, err := plot.New()
     ....
     lpPoints.Shape = draw.CircleGlyph{}
     lpPoints.Color = color.RGBA{R: 255, G: 200, B: 200, A: 255}
     lpPoints.Width = vg.Points(1.0)
     lpPoints.LineColor = lpLine.Color
     p.Add(lpLine, lpPoints)

vg/draw/canvas.go

@@ -55,6 +55,12 @@ type GlyphStyle struct {
 	// Radius specifies the size of the glyph's radius.
 	Radius vg.Length
 
+	// Width is set, LineColour is used to outline the glyph
+	Width vg.Length
+
+	// Outline glyph with this color if Width is set.
+	LineColor color.Color
+
 	// Shape draws the shape of the glyph.
 	Shape GlyphDrawer
 }
@@ -106,6 +112,11 @@ func (CircleGlyph) DrawGlyph(c *Canvas, sty GlyphStyle, pt vg.Point) {
 	p.Arc(pt, sty.Radius, 0, 2*math.Pi)
 	p.Close()
 	c.Fill(p)
+
+	if sty.Width > 0 {
+		c.SetLineStyle(LineStyle{Color: sty.LineColor, Width: sty.Width})
+		c.Stroke(p)
+	}
 }
 
 // RingGlyph is a glyph that draws the outline of a circle.
@@ -156,6 +167,11 @@ func (BoxGlyph) DrawGlyph(c *Canvas, sty GlyphStyle, pt vg.Point) {
 	p.Line(vg.Point{X: pt.X - x, Y: pt.Y + x})
 	p.Close()
 	c.Fill(p)
+
+	if sty.Width > 0 {
+		c.SetLineStyle(LineStyle{Color: sty.LineColor, Width: sty.Width})
+		c.Stroke(p)
+	}
 }
 
 // TriangleGlyph is a glyph that draws the outline of a triangle.
@@ -185,6 +201,11 @@ func (PyramidGlyph) DrawGlyph(c *Canvas, sty GlyphStyle, pt vg.Point) {
 	p.Line(vg.Point{X: pt.X + r*cosπover6, Y: pt.Y - r*sinπover6})
 	p.Close()
 	c.Fill(p)
+
+	if sty.Width > 0 {
+		c.SetLineStyle(LineStyle{Color: sty.LineColor, Width: sty.Width})
+		c.Stroke(p)
+	}
 }
 
 // PlusGlyph is a glyph that draws a plus sign

[Sebastien Binet]

Created by: kortschak

How about using a LineStyle here? Comment would be:

// LineStyle is the style of the glyph outline.
// If LineStyle.Width is zero no outline is drawn.

[Sebastien Binet]

Created by: zaddok

Great suggestion, I would like that idea, except for the fact that LineStyle also includes a Dashes and a DashOffs field—they would be effectively unused. I'm happy to switch the patch over to use LineStyle if that is what people prefer.

PS: Yikes, I need to fix the wording of that comment as well.

[Sebastien Binet]

Created by: kortschak

There's no reason not to allow dashed outlines for glyphs.