diff --git a/backend/svg/backend.go b/backend/svg/backend.go
index 1e85a0e..e4a8a7a 100644
--- a/backend/svg/backend.go
+++ b/backend/svg/backend.go
@@ -54,7 +54,8 @@ func newBackend(out io.Writer, w, h int, dpr float64, o options) *backend {
}
// The ids the accessible title and description are written under. A document
-// has one chart in it, so they need no counter.
+// has one chart in it, so they need no counter; [IDPrefix] is what keeps two
+// documents on one page apart.
const (
titleID = "figure-title"
descID = "figure-desc"
@@ -74,11 +75,11 @@ func (b *backend) accessibilityAttrs(head *bytes.Buffer) {
head.WriteString(` role="img" aria-labelledby="`)
switch {
case b.desc.Title != "" && b.desc.Detail != "":
- head.WriteString(titleID + " " + descID)
+ head.WriteString(b.opts.idPrefix + titleID + " " + b.opts.idPrefix + descID)
case b.desc.Title != "":
- head.WriteString(titleID)
+ head.WriteString(b.opts.idPrefix + titleID)
default:
- head.WriteString(descID)
+ head.WriteString(b.opts.idPrefix + descID)
}
head.WriteString(`"`)
}
@@ -88,13 +89,13 @@ func (b *backend) accessibilityAttrs(head *bytes.Buffer) {
// reader should find them.
func (b *backend) accessibilityElements(head *bytes.Buffer) {
if b.desc.Title != "" {
- head.WriteString(``)
+ head.WriteString(`<title id="` + b.opts.idPrefix + titleID + `">`)
xmlEscape(head, b.desc.Title)
head.WriteString(``)
b.nl(head)
}
if b.desc.Detail != "" {
- head.WriteString(``)
+ head.WriteString(``)
xmlEscape(head, b.desc.Detail)
head.WriteString(``)
b.nl(head)
@@ -103,7 +104,7 @@ func (b *backend) accessibilityElements(head *bytes.Buffer) {
func (b *backend) id(prefix string) string {
b.nextID++
- return prefix + strconv.Itoa(b.nextID)
+ return b.opts.idPrefix + prefix + strconv.Itoa(b.nextID)
}
// nl writes a newline in pretty mode and nothing otherwise, so the compact and
diff --git a/backend/svg/svg_test.go b/backend/svg/svg_test.go
index 0f729b7..3da4679 100644
--- a/backend/svg/svg_test.go
+++ b/backend/svg/svg_test.go
@@ -176,6 +176,59 @@ func TestClipAndTransformGroup(t *testing.T) {
}
}
+// Two documents inlined into one page share an id namespace, and both count
+// from one. Every id a document defines, and every reference to one, has to
+// carry the prefix, or the second chart's cells are clipped to the first's
+// panel and its aria-labelledby reads the first one's title.
+func TestIDPrefixReachesEveryIdAndReference(t *testing.T) {
+ b, finish := open(t, svg.IDPrefix("chart2-"))
+ b.(ir.Semantics).Describe(ir.Description{Title: "T", Detail: "D"})
+ var clip ir.Path
+ clip.Rect(ir.R(0, 0, 50, 50))
+ b.Push(&clip, ir.Affine{A: 1, D: 1})
+ b.Markers(ir.MarkerCircle, []ir.Point{{X: 1, Y: 1}}, ir.MarkerStyle{Size: 6, Fill: ir.RGB(0, 128, 0)})
+ var p ir.Path
+ p.Rect(ir.R(0, 0, 10, 10))
+ b.FillPath(&p, ir.Fill{
+ Color: ir.RGB(0, 0, 0), End: ir.Point{X: 10},
+ Stops: []ir.GradientStop{{Offset: 0, Color: ir.RGB(0, 0, 0)}, {Offset: 1, Color: ir.RGB(255, 255, 255)}},
+ }, ir.NonZero)
+ b.Pop()
+ got := finish()
+
+ for _, want := range []string{
+ ``, `clip-path="url(#chart2-c1)"`,
+ ``, ``,
+ } {
+ if !strings.Contains(got, want) {
+ t.Errorf("missing %s in:\n%s", want, got)
+ }
+ }
+ for _, unprefixed := range []string{`id="c1"`, `id="m2"`, `id="g3"`, `id="figure-`, `"#c1`, `"#m2`, `(#c1`, `(#g3`, `="figure-`, `"figure-`} {
+ if strings.Contains(got, unprefixed) {
+ t.Errorf("found unprefixed %s in:\n%s", unprefixed, got)
+ }
+ }
+}
+
+func TestABadIDPrefixIsReportedOnOpen(t *testing.T) {
+ for _, p := range []string{"1chart", "-x", `a"b`, "a b", "รค"} {
+ var buf bytes.Buffer
+ if _, err := svg.Writer(&buf, svg.IDPrefix(p)).Open(ir.Surface{WidthPx: 10, HeightPx: 10, DPR: 1}); err == nil {
+ t.Errorf("IDPrefix(%q) opened without an error", p)
+ }
+ }
+ for _, p := range []string{"", "a", "_x", "chart-2.", "Fig_3-"} {
+ var buf bytes.Buffer
+ if _, err := svg.Writer(&buf, svg.IDPrefix(p)).Open(ir.Surface{WidthPx: 10, HeightPx: 10, DPR: 1}); err != nil {
+ t.Errorf("IDPrefix(%q): %v", p, err)
+ }
+ }
+}
+
func TestUnbalancedPushIsAnError(t *testing.T) {
var buf bytes.Buffer
target := svg.Writer(&buf)
diff --git a/backend/svg/target.go b/backend/svg/target.go
index 249a4b8..da49053 100644
--- a/backend/svg/target.go
+++ b/backend/svg/target.go
@@ -18,6 +18,8 @@ type options struct {
fontFail error
family string
pretty bool
+ idPrefix string
+ idFail error
}
// WithFont supplies a TrueType or OpenType file whose metrics are used for
@@ -47,6 +49,44 @@ func WithFontFamily(family string) Option {
// smaller, and golden files are diffed by tooling rather than read.
func Pretty() Option { return func(o *options) { o.pretty = true } }
+// IDPrefix puts p in front of every id the document defines: its clip paths,
+// marker shapes and gradients, and the and <desc> its aria-labelledby
+// names.
+//
+// A standalone file needs none, which is why the default is no prefix and
+// leaves the output byte for byte as it was. It is for several documents
+// inlined into one HTML page, which share one id namespace: every chart counts
+// its ids from one, so the second chart's url(#c1) resolves to the first
+// chart's clip and its cells are cut to the wrong rectangle, and its
+// aria-labelledby reads out the first chart's title. Give each document its own
+// prefix โ "sales-", "chart2-" โ and they cannot meet.
+//
+// p must be usable at the front of an XML name: an ASCII letter or underscore,
+// then letters, digits, '-', '_' or '.'. Anything else is reported on Open
+// rather than written into an attribute it would break.
+func IDPrefix(p string) Option {
+ return func(o *options) {
+ if !validPrefix(p) {
+ o.idFail = fmt.Errorf("id prefix %q is not the start of an XML name", p)
+ return
+ }
+ o.idPrefix = p
+ }
+}
+
+func validPrefix(p string) bool {
+ for i := 0; i < len(p); i++ {
+ c := p[i]
+ switch {
+ case c >= 'a' && c <= 'z', c >= 'A' && c <= 'Z', c == '_':
+ case i > 0 && (c >= '0' && c <= '9' || c == '-' || c == '.'):
+ default:
+ return false
+ }
+ }
+ return true
+}
+
// Writer returns a Target that writes an SVG document to w.
func Writer(w io.Writer, opts ...Option) ir.Target {
return &target{w: nopCloser{w}, opts: build(opts)}
@@ -78,6 +118,9 @@ func (t *target) Open(s ir.Surface) (ir.Backend, error) {
if t.opts.fontFail != nil {
return nil, fmt.Errorf("figure/backend/svg: %w", t.opts.fontFail)
}
+ if t.opts.idFail != nil {
+ return nil, fmt.Errorf("figure/backend/svg: %w", t.opts.idFail)
+ }
if t.w == nil {
f, err := os.Create(t.path)
if err != nil {
diff --git a/geom/text.go b/geom/text.go
index e9d7caa..a6144f4 100644
--- a/geom/text.go
+++ b/geom/text.go
@@ -61,6 +61,10 @@ import (
// A layer given [ColorBy] takes each label's ink from the fill that scale
// gives the row, dark on light and light on dark, so that a qualitative
// palette does not leave half its categories unreadable. [Color] overrides it.
+// The layer reads only its own options, never the layer under it: labels over
+// a heatmap need the heatmap's ColorBy repeated on the text layer, with the
+// same scale value so the two agree and the chart keeps one colourbar โ
+// without it every label is drawn in the theme's label ink, dark on dark cells.
//
// AvoidOverlap opts into the renderer's panel-local label layout. Point labels
// may move; box labels remain anchored to their own box and are dropped if they