area and line titles

fixes #94

Author: Fil

src/mark.js

@@ -186,6 +186,14 @@ export function title(L) {
       .text(i => L[i]) : () => {};
 }
 
+// title for groups (lines, areas).
+export function titleGroup(L) {
+  return L ? selection => selection
+    .filter(([i]) => nonempty(L[i]))
+    .append("title")
+      .text(([i]) => L[i]) : () => {};
+}
+
 // Returns a Uint32Array with elements [0, 1, 2, … data.length - 1].
 export function range(data) {
   return Uint32Array.from(data, indexOf);

src/marks/area.js

@@ -3,7 +3,7 @@ import {create} from "d3-selection";
 import {area as shapeArea} from "d3-shape";
 import {Curve} from "../curve.js";
 import {defined} from "../defined.js";
-import {Mark, indexOf, maybeColor, maybeZero, maybeSort, title} from "../mark.js";
+import {Mark, indexOf, maybeColor, maybeZero, maybeSort, titleGroup} from "../mark.js";
 import {Style, applyDirectStyles, applyIndirectStyles, applyTransform} from "../style.js";
 
 export class Area extends Mark {
@@ -62,7 +62,7 @@ export class Area extends Mark {
               .y0(i => y(Y1[i]))
               .x1(i => x(X2[i]))
               .y1(i => y(Y2[i])))
-            .call(title(L)))
+            .call(titleGroup(L)))
       .node();
   }
 }

src/marks/line.js

@@ -3,7 +3,7 @@ import {create} from "d3-selection";
 import {line as shapeLine} from "d3-shape";
 import {Curve} from "../curve.js";
 import {defined} from "../defined.js";
-import {Mark, indexOf, identity, first, second, maybeColor, maybeSort, title} from "../mark.js";
+import {Mark, indexOf, identity, first, second, maybeColor, maybeSort, titleGroup} from "../mark.js";
 import {Style, applyDirectStyles, applyIndirectStyles, applyTransform} from "../style.js";
 
 export class Line extends Mark {
@@ -61,7 +61,7 @@ export class Line extends Mark {
               .defined(i => defined(X[i]) && defined(Y[i]))
               .x(i => x(X[i]))
               .y(i => y(Y[i])))
-            .call(title(L)))
+            .call(titleGroup(L)))
       .node();
   }
 }