color scale override for Plot.raster (#1318)

* closes #1317

* Update src/marks/raster.js

Co-authored-by: Mike Bostock <mbostock@gmail.com>

* don't hardcode that fill is scaled with {color}

* expose channel states to render

---------

Co-authored-by: Mike Bostock <mbostock@gmail.com>

Author: Fil

src/channel.d.ts

@@ -82,3 +82,9 @@ export type ChannelDomainSort = {
 } & ChannelDomainOptions;
 
 export type ChannelReducers = {[key in ChannelName]?: ChannelReducerSpec | null};
+
+/** The abstract (unscaled) values, and associated scale, per channel. */
+export type ChannelStates = {[key in ChannelName]?: {value: any[]; scale: ScaleName | null}};
+
+/** The possibly-scaled values for each channel. */
+export type ChannelValues = {[key in ChannelName]?: any[]} & {channels: ChannelStates};

src/channel.js

@@ -24,12 +24,14 @@ export function createChannels(channels, data) {
 
 // TODO Use Float64Array for scales with numeric ranges, e.g. position?
 export function valueObject(channels, scales) {
-  return Object.fromEntries(
+  const values = Object.fromEntries(
     Object.entries(channels).map(([name, {scale: scaleName, value}]) => {
       const scale = scaleName == null ? null : scales[scaleName];
       return [name, scale == null ? value : map(value, scale)];
     })
   );
+  values.channels = channels; // expose channel state for advanced usage
+  return values;
 }
 
 // If the channel uses the "auto" scale (or equivalently true), infer the scale

src/mark.d.ts

@@ -1,10 +1,10 @@
-import type {Channels, ChannelDomainSort, ChannelName, ChannelValue, ChannelValueSpec} from "./channel.js";
+import type {ChannelDomainSort, Channels, ChannelValue, ChannelValues, ChannelValueSpec} from "./channel.js";
 import type {Context} from "./context.js";
 import type {Dimensions} from "./dimensions.js";
 import type {Facet, FacetAnchor} from "./facet.js";
 import type {plot} from "./plot.js";
 import type {ScaleFunctions} from "./scales.js";
-import type {InitializerFunction, TransformFunction, SortOrder} from "./transforms/basic.js";
+import type {InitializerFunction, SortOrder, TransformFunction} from "./transforms/basic.js";
 
 export type FrameAnchor =
   | "middle"
@@ -22,7 +22,7 @@ export type Data = Iterable<any> | ArrayLike<any>;
 export type RenderFunction = (
   index: number[],
   scales: ScaleFunctions,
-  values: {[key in ChannelName]?: any[]},
+  values: ChannelValues,
   dimensions: Dimensions,
   context: Context
 ) => SVGElement | null;

src/marks/raster.js

@@ -97,11 +97,11 @@ export class Raster extends AbstractRaster {
   scale(channels, {color, ...scales}, context) {
     return super.scale(channels, scales, context);
   }
-  render(index, scales, channels, dimensions, context) {
-    const color = scales.color ?? ((x) => x);
-    const {x: X, y: Y} = channels;
+  render(index, scales, values, dimensions, context) {
+    const color = scales[values.channels.fill?.scale] ?? ((x) => x);
+    const {x: X, y: Y} = values;
     const {document} = context;
-    const [x1, y1, x2, y2] = renderBounds(channels, dimensions, context);
+    const [x1, y1, x2, y2] = renderBounds(values, dimensions, context);
     const dx = x2 - x1;
     const dy = y2 - y1;
     const {pixelSize: k, width: w = Math.round(Math.abs(dx) / k), height: h = Math.round(Math.abs(dy) / k)} = this;
@@ -110,7 +110,7 @@ export class Raster extends AbstractRaster {
     // Interpolate the samples to fill the raster grid. If interpolate is null,
     // then a continuous function is being sampled, and the raster grid is
     // already aligned with the canvas.
-    let {fill: F, fillOpacity: FO} = channels;
+    let {fill: F, fillOpacity: FO} = values;
     let offset = 0;
     if (this.interpolate) {
       const kx = w / dx;

test/output/rasterVapor2.html

@@ -17,6 +17,25 @@ export async function rasterVapor() {
   });
 }
 
+export async function rasterVapor2() {
+  return Plot.plot({
+    color: {scheme: "blues", legend: true},
+    x: {transform: (x) => x - 180},
+    y: {transform: (y) => 90 - y},
+    marks: [
+      Plot.raster(await vapor(), {
+        width: 360,
+        height: 180
+      }),
+      Plot.raster(await vapor(), {
+        width: 360,
+        height: 180,
+        fill: {value: (d) => (d > 4 ? "red" : null), scale: null}
+      })
+    ]
+  });
+}
+
 export async function contourVapor() {
   return Plot.plot({
     width: 960,