vg/vgsvg: drop fontMap, use informations from font.Font

This CL drops the use of the internal fontMap that was associating some
pre-defined set of fonts with a set of SVG naming schemes (derived from
PostScript).
Instead, use the informations contained in plot/font.Font to derive the
expected SVG font-family (and friends) font style string.

Updates #702.

vg/vgsvg/font_test.go

@@ -0,0 +1,171 @@
+// Copyright ©2021 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package vgsvg
+
+import (
+	"testing"
+
+	stdfnt "golang.org/x/image/font"
+	"gonum.org/v1/plot/font"
+)
+
+func TestSVGFontDescr(t *testing.T) {
+	for i, tc := range []struct {
+		fnt  font.Font
+		want string
+	}{
+		// typefaces
+		{
+			fnt:  font.Font{Typeface: "Liberation"},
+			want: "font-family:Liberation;font-variant:normal;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation;font-variant:normal;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "My-Font-Name",
+				Variant:  "",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:My-Font-Name;font-variant:normal;font-weight:normal;font-style:normal",
+		},
+		// variants
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "Mono",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation, monospace;font-variant:monospace;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "Serif",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation, serif;font-variant:serif;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "Sans",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation, sans-serif;font-variant:sans-serif;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "SansSerif",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation, sans-serif;font-variant:sans-serif;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "Sans-Serif",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation, sans-serif;font-variant:sans-serif;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "Smallcaps",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation, small-caps;font-variant:small-caps;font-weight:normal;font-style:normal",
+		},
+		// styles
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "",
+				Style:    stdfnt.StyleItalic,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation;font-variant:normal;font-weight:normal;font-style:italic",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "",
+				Style:    stdfnt.StyleOblique,
+				Weight:   stdfnt.WeightNormal,
+			},
+			want: "font-family:Liberation;font-variant:normal;font-weight:normal;font-style:oblique",
+		},
+		// weights
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightThin,
+			},
+			want: "font-family:Liberation;font-variant:normal;font-weight:100;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightBold,
+			},
+			want: "font-family:Liberation;font-variant:normal;font-weight:bold;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "",
+				Style:    stdfnt.StyleNormal,
+			},
+			want: "font-family:Liberation;font-variant:normal;font-weight:normal;font-style:normal",
+		},
+		{
+			fnt: font.Font{
+				Typeface: "Liberation",
+				Variant:  "",
+				Style:    stdfnt.StyleNormal,
+				Weight:   stdfnt.WeightExtraBold,
+			},
+			want: "font-family:Liberation;font-variant:normal;font-weight:800;font-style:normal",
+		},
+		// weights+styles
+		{
+			fnt: font.Font{
+				Typeface: "Times",
+				Variant:  "",
+				Style:    stdfnt.StyleItalic,
+				Weight:   stdfnt.WeightBold,
+			},
+			want: "font-family:Times;font-variant:normal;font-weight:bold;font-style:italic",
+		},
+	} {
+		got := svgFontDescr(tc.fnt)
+		if got != tc.want {
+			t.Errorf(
+				"invalid SVG font[%d] description:\ngot= %s\nwant=%s",
+				i, got, tc.want,
+			)
+		}
+	}
+}