Use context2D to convert CSS4 colors to display-p3

docs/marks/raster.md

@@ -286,11 +286,12 @@ If **width** is specified, **x1** defaults to 0 and **x2** defaults to **width**
 
 The following raster-specific constant options are supported:
 
+* **colorSpace** - the [color space](https://developer.mozilla.org/en-US/docs/Web/API/ImageData/colorSpace) <VersionBadge pr="2143" />
 * **interpolate** - the [spatial interpolation method](#spatial-interpolators)
 * **imageRendering** - the [image-rendering attribute](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/image-rendering); defaults to *auto* (bilinear)
 * **blur** - a non-negative pixel radius for smoothing; defaults to 0
 
-The **imageRendering** option may be set to *pixelated* for a sharper image. The **interpolate** option is ignored when **fill** or **fillOpacity** is a function of *x* and *y*.
+The **colorSpace** may be set to *display-p3* for the Display P3 color space. The **imageRendering** option may be set to *pixelated* for a sharper image. The **interpolate** option is ignored when **fill** or **fillOpacity** is a function of *x* and *y*.
 
 ## raster(*data*, *options*) {#raster}
 

src/marks/raster.d.ts

@@ -145,6 +145,14 @@ export interface RasterOptions extends Omit<MarkOptions, "fill" | "fillOpacity">
    */
   imageRendering?: string;
 
+  /**
+   * The [color space][1] of the backing canvas. Defaults to *srgb*; set to
+   * *display-p3* for the Display P3 color space.
+   *
+   * [1]: https://developer.mozilla.org/en-US/docs/Web/API/ImageData/colorSpace
+   */
+  colorSpace?: "srgb" | "display-p3" | string;
+
   /**
    * The fill, typically bound to the *color* scale. Can be specified as a
    * constant, a channel based on the sample *data*, or as a function *f*(*x*,

src/marks/raster.js

@@ -36,6 +36,7 @@ export class AbstractRaster extends Mark {
       y1 = y == null ? 0 : undefined,
       x2 = x == null ? width : undefined,
       y2 = y == null ? height : undefined,
+      colorSpace = "srgb",
       pixelSize = defaults.pixelSize,
       blur = 0,
       interpolate
@@ -79,6 +80,7 @@ export class AbstractRaster extends Mark {
     this.pixelSize = number(pixelSize, "pixelSize");
     this.blur = number(blur, "blur");
     this.interpolate = x == null || y == null ? null : maybeInterpolate(interpolate); // interpolation requires x & y
+    this.colorSpace = String(colorSpace);
   }
 }
 
@@ -125,15 +127,19 @@ export class Raster extends AbstractRaster {
     // function, offset into the dense grid based on the current facet index.
     else if (this.data == null && index) offset = index.fi * n;
 
+    // Color space and CSS4 color conversion
+    const colorBytes = converter(this.colorSpace);
+
     // Render the raster grid to the canvas, blurring if needed.
     const canvas = document.createElement("canvas");
     canvas.width = w;
     canvas.height = h;
-    const context2d = canvas.getContext("2d");
+    const context2d = canvas.getContext("2d", {colorSpace: this.colorSpace});
     const image = context2d.createImageData(w, h);
     const imageData = image.data;
-    let {r, g, b} = rgb(this.fill) ?? {r: 0, g: 0, b: 0};
-    let a = (this.fillOpacity ?? 1) * 255;
+    const fo = this.fillOpacity ?? 1;
+    let {r, g, b, opacity: co = 1} = colorBytes(this.fill) ?? {r: 0, g: 0, b: 0};
+    let a = co * fo * 255;
     for (let i = 0; i < n; ++i) {
       const j = i << 2;
       if (F) {
@@ -142,9 +148,10 @@ export class Raster extends AbstractRaster {
           imageData[j + 3] = 0;
           continue;
         }
-        ({r, g, b} = rgb(fi));
+        ({r, g, b, opacity: co = 1} = colorBytes(fi));
+        if (!FO) a = co * fo * 255;
       }
-      if (FO) a = FO[i + offset] * 255;
+      if (FO) a = co * FO[i + offset] * 255;
       imageData[j + 0] = r;
       imageData[j + 1] = g;
       imageData[j + 2] = b;
@@ -502,3 +509,24 @@ function denseY(y1, y2, width, height) {
     }
   };
 }
+
+// Color space and CSS4 conversions
+export function converter(colorSpace) {
+  const canvas = document.createElement("canvas");
+  canvas.width = 1;
+  canvas.height = 1;
+  const context = canvas.getContext("2d", {colorSpace, willReadFrequently: true});
+  const mem = new Map();
+  const canvasConverter = (c) => {
+    if (mem.has((c = String(c)))) return mem.get(c);
+    context.fillStyle = c;
+    context.clearRect(0, 0, 1, 1);
+    context.fillRect(0, 0, 1, 1);
+    const [r, g, b, a] = context.getImageData(0, 0, 1, 1).data;
+    const color = {r, g, b, opacity: a / 255};
+    if (mem.size < 256) mem.set(c, color);
+    return color;
+  };
+  let p;
+  return colorSpace === "srgb" ? (c) => (isNaN((p = rgb(c)).opacity) ? canvasConverter(c) : p) : canvasConverter;
+}