defalt z: null for redundant color encoding

Author: mbostock

src/marks/area.js

@@ -77,11 +77,11 @@ export function area(data, options) {
 }
 
 export function areaX(data, options) {
-  const {y = indexOf, ...rest} = maybeDenseIntervalY(options);
-  return new Area(data, maybeStackX(maybeIdentityX({...rest, y1: y, y2: undefined}, y === indexOf ? "x2" : "x")));
+  const {x, y = indexOf, fill, z = x === fill ? null : undefined, ...rest} = maybeDenseIntervalY(options);
+  return new Area(data, maybeStackX(maybeIdentityX({...rest, x, y1: y, y2: undefined, z, fill}, y === indexOf ? "x2" : "x")));
 }
 
 export function areaY(data, options) {
-  const {x = indexOf, ...rest} = maybeDenseIntervalX(options);
-  return new Area(data, maybeStackY(maybeIdentityY({...rest, x1: x, x2: undefined}, x === indexOf ? "y2" : "y")));
+  const {x = indexOf, y, fill, z = y === fill ? null : undefined, ...rest} = maybeDenseIntervalX(options);
+  return new Area(data, maybeStackY(maybeIdentityY({...rest, x1: x, x2: undefined, y, z, fill}, x === indexOf ? "y2" : "y")));
 }

src/marks/line.js

@@ -103,10 +103,10 @@ export function line(data, {x, y, ...options} = {}) {
   return new Line(data, {...options, x, y});
 }
 
-export function lineX(data, {x = identity, y = indexOf, ...options} = {}) {
-  return new Line(data, maybeDenseIntervalY({...options, x, y}));
+export function lineX(data, {x = identity, y = indexOf, stroke, z = stroke === x ? null : undefined, ...options} = {}) {
+  return new Line(data, maybeDenseIntervalY({...options, x, y, z, stroke}));
 }
 
-export function lineY(data, {x = indexOf, y = identity, ...options} = {}) {
-  return new Line(data, maybeDenseIntervalX({...options, x, y}));
+export function lineY(data, {x = indexOf, y = identity, stroke, z = stroke === y ? null : undefined, ...options} = {}) {
+  return new Line(data, maybeDenseIntervalX({...options, x, y, z, stroke}));
 }