Convert shading colors in bulk, rather than one at a time

The axial/radial ramps and the function-based lattice converted one color per
call, i.e. one Wasm round-trip each for `IccColorSpace` (hence for
`/DeviceCMYK`). Add `ColorSpace.getRgbItems`, overridden by `IccColorSpace` and
`AlternateCS`, to convert a whole batch at once.

src/core/colorspace.js

@@ -183,6 +183,21 @@ class ColorSpace {
     unreachable("Should not call ColorSpace.getRgbBuffer");
   }
 
+  /**
+   * Converts `count` unscaled colors to RGB, starting at `destOffset`.
+   * Components use the native color-space ranges expected by `getRgbItem`,
+   * and each output has a `3 + alpha01` byte stride.
+   * Subclasses may override this to batch expensive conversions.
+   */
+  getRgbItems(src, count, dest, destOffset, alpha01) {
+    const { numComps } = this;
+
+    for (let i = 0, srcOffset = 0; i < count; i++, srcOffset += numComps) {
+      this.getRgbItem(src, srcOffset, dest, destOffset);
+      destOffset += 3 + alpha01;
+    }
+  }
+
   /**
    * Determines the number of bytes required to store the result of the
    * conversion done by the getRgbBuffer method. As in getRgbBuffer,
@@ -379,6 +394,20 @@ class AlternateCS extends ColorSpace {
     this.base.getRgbItem(tmpBuf, 0, dest, destOffset);
   }
 
+  getRgbItems(src, count, dest, destOffset, alpha01) {
+    const { base, numComps, tintFn } = this;
+    const baseNumComps = base.numComps;
+    // Tint first so the base color space can convert the batch at once.
+    const tinted = new Float32Array(count * baseNumComps);
+
+    for (let i = 0, srcOffset = 0, tintedOffset = 0; i < count; i++) {
+      tintFn(src, srcOffset, tinted, tintedOffset);
+      srcOffset += numComps;
+      tintedOffset += baseNumComps;
+    }
+    base.getRgbItems(tinted, count, dest, destOffset, alpha01);
+  }
+
   getRgbBuffer(src, srcOffset, count, dest, destOffset, bits, alpha01) {
     if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
       assert(

src/core/icc_colorspace.js

@@ -117,6 +117,21 @@ class IccColorSpace extends ColorSpace {
     QCMS._destBuffer = null;
   }
 
+  getRgbItems(src, count, dest, destOffset, alpha01) {
+    const { numComps } = this;
+    const length = count * numComps;
+    const scaled = new Uint8Array(length);
+    // Uint8Array matches the truncation and wrapping of the scalar Wasm calls.
+    for (let i = 0; i < length; i++) {
+      scaled[i] = src[i] * 255;
+    }
+    QCMS._destBuffer = dest;
+    QCMS._destOffset = destOffset;
+    QCMS._destLength = count * (3 + alpha01);
+    qcms_convert_array(this.#transformer, scaled);
+    QCMS._destBuffer = null;
+  }
+
   getRgbBuffer(src, srcOffset, count, dest, destOffset, bits, alpha01) {
     src = src.subarray(srcOffset, srcOffset + count * this.numComps);
     if (bits !== 8) {

src/core/pattern.js

@@ -46,6 +46,17 @@ const ShadingType = {
   TENSOR_PATCH_MESH: 7,
 };
 
+// Bound temporary buffers; DeviceN component counts come from the PDF.
+const MAX_SAMPLED_COLOR_COMPONENTS = 1 << 16;
+
+function getColorConversionBatchSize(count, numComps) {
+  return MathClamp(
+    Math.floor(MAX_SAMPLED_COLOR_COMPONENTS / numComps),
+    1,
+    count
+  );
+}
+
 class Pattern {
   // eslint-disable-next-line no-unused-private-class-members
   static #hasGPU = false;
@@ -202,22 +213,32 @@ class RadialAxialShading extends BaseShading {
       return;
     }
 
-    const color = new Float32Array(cs.numComps),
-      ratio = new Float32Array(1);
+    const { numComps } = cs;
+    const ratio = new Float32Array(1);
+
+    // Batch colors to reduce ICC Wasm calls and bound temporary memory.
+    const batchSize = getColorConversionBatchSize(NUMBER_OF_SAMPLES, numComps);
+    const comps = new Float32Array(batchSize * numComps);
+    const rgb = new Uint8ClampedArray(NUMBER_OF_SAMPLES * 3);
+    for (let start = 0; start < NUMBER_OF_SAMPLES; start += batchSize) {
+      const count = Math.min(batchSize, NUMBER_OF_SAMPLES - start);
+      for (let i = 0, offset = 0; i < count; i++, offset += numComps) {
+        ratio[0] = t0 + (start + i) * step;
+        fn(ratio, 0, comps, offset);
+      }
+      cs.getRgbItems(comps, count, rgb, start * 3, /* alpha01 = */ 0);
+    }
 
     let iBase = 0;
-    ratio[0] = t0;
-    fn(ratio, 0, color, 0);
-    const rgbBuffer = new Uint8ClampedArray(3);
-    cs.getRgb(color, 0, rgbBuffer);
-    let [rBase, gBase, bBase] = rgbBuffer;
+    let rBase = rgb[0],
+      gBase = rgb[1],
+      bBase = rgb[2];
     colorStops.push([0, Util.makeHexColor(rBase, gBase, bBase)]);
 
     let iPrev = 1;
-    ratio[0] = t0 + step;
-    fn(ratio, 0, color, 0);
-    cs.getRgb(color, 0, rgbBuffer);
-    let [rPrev, gPrev, bPrev] = rgbBuffer;
+    let rPrev = rgb[3],
+      gPrev = rgb[4],
+      bPrev = rgb[5];
 
     // Slopes are rise / run.
     // A max slope is from the least value the base component could have been
@@ -236,10 +257,10 @@ class RadialAxialShading extends BaseShading {
     let minSlopeB = bPrev - bBase - 1;
 
     for (let i = 2; i < NUMBER_OF_SAMPLES; i++) {
-      ratio[0] = t0 + i * step;
-      fn(ratio, 0, color, 0);
-      cs.getRgb(color, 0, rgbBuffer);
-      const [r, g, b] = rgbBuffer;
+      const rgbOffset = i * 3;
+      const r = rgb[rgbOffset],
+        g = rgb[rgbOffset + 1],
+        b = rgb[rgbOffset + 2];
 
       // Keep going if the maximum minimum slope <= the minimum maximum slope.
       // Otherwise add a rgbPrev color stop and make it the new base.
@@ -499,13 +520,18 @@ class FunctionBasedShading extends BaseShading {
     const coords = (this.coords = new Float32Array(totalVertices * 2));
     const colors = (this.colors = new Uint8ClampedArray(totalVertices * 4));
 
+    const { numComps } = cs;
     const xyBuf = new Float32Array(2);
-    const colorBuf = new Float32Array(cs.numComps);
+    // Batch colors to reduce ICC Wasm calls and bound temporary memory.
+    const batchSize = getColorConversionBatchSize(totalVertices, numComps);
+    const comps = new Float32Array(batchSize * numComps);
     const rangeX = (x1 - x0) / stepsX;
     const rangeY = (y1 - y0) / stepsY;
     const halfStepX = rangeX / 2;
     const halfStepY = rangeY / 2;
     let coordOffset = 0;
+    let compOffset = 0;
+    let batchCount = 0;
     let colorOffset = 0;
     for (let row = 0; row <= stepsY; row++) {
       const yDomain = y0 + rangeY * row;
@@ -515,16 +541,32 @@ class FunctionBasedShading extends BaseShading {
       for (let col = 0; col <= stepsX; col++) {
         const xDomain = x0 + rangeX * col;
         xyBuf[0] = col === stepsX ? xDomain - halfStepX : xDomain;
-        fn(xyBuf, 0, colorBuf, 0);
+        fn(xyBuf, 0, comps, compOffset);
+        compOffset += numComps;
+        batchCount++;
+
         coords[coordOffset] = xDomain;
         coords[coordOffset + 1] = yDomain;
         Util.applyTransform(coords, matrix, coordOffset);
         coordOffset += 2;
 
-        cs.getRgbItem(colorBuf, 0, colors, colorOffset);
-        colorOffset += 4; // alpha — unused, stays 0
+        if (batchCount === batchSize) {
+          cs.getRgbItems(
+            comps,
+            batchCount,
+            colors,
+            colorOffset,
+            /* alpha01 = */ 1
+          );
+          colorOffset += batchCount * 4;
+          compOffset = batchCount = 0;
+        }
       }
     }
+    if (batchCount > 0) {
+      cs.getRgbItems(comps, batchCount, colors, colorOffset, /* alpha01 = */ 1);
+    }
+    // Alpha stays zero.
 
     const ps = new Uint32Array(totalVertices);
     for (let i = 0; i < totalVertices; i++) {

test/pdfs/.gitignore

@@ -949,3 +949,4 @@
 !jpx_smaskindata.pdf
 !nonisolated_blend_smask.pdf
 !signed_verified.pdf
+!function_based_shading_cmyk.pdf

test/test_manifest.json

@@ -14508,5 +14508,13 @@
     "md5": "4b87611416be34894eeb19c158fafbad",
     "rounds": 1,
     "type": "eq"
+  },
+  {
+    "id": "function_based_shading_cmyk",
+    "file": "pdfs/function_based_shading_cmyk.pdf",
+    "md5": "6c2b4d131a007a6f40ac7a892ad5f2a1",
+    "rounds": 1,
+    "lastPage": 1,
+    "type": "eq"
   }
 ]

test/unit/colorspace_spec.js

@@ -53,6 +53,21 @@ describe("colorspace", function () {
     });
   });
 
+  describe("ColorSpace.getRgbItems", function () {
+    it("should honor the destination offset and alpha stride", function () {
+      const src = new Float32Array([0, 0.25, 0.5, 1, 0.75, 0.5, 0.1, 0.2, 0.3]);
+      const dest = new Uint8ClampedArray(14).fill(9);
+
+      ColorSpaceUtils.rgb.getRgbItems(src, 3, dest, 1, /* alpha01 = */ 1);
+
+      expect(dest).toEqual(
+        new Uint8ClampedArray([
+          9, 0, 64, 128, 9, 255, 191, 128, 9, 26, 51, 77, 9, 9,
+        ])
+      );
+    });
+  });
+
   describe("ColorSpace caching", function () {
     let globalColorSpaceCache, localColorSpaceCache;
 

test/unit/pattern_spec.js

@@ -37,7 +37,12 @@ describe("pattern", function () {
     } = {}) {
       const dict = new Dict();
       dict.set("ShadingType", 1);
-      dict.set("ColorSpace", Name.get(colorSpace));
+      if (Array.isArray(colorSpace)) {
+        // `setIfName` only accepts a name, and would silently drop an Array.
+        dict.set("ColorSpace", colorSpace);
+      } else {
+        dict.setIfName("ColorSpace", colorSpace);
+      }
       dict.set("Domain", domain);
       dict.set("Matrix", matrix);
       if (background) {
@@ -86,6 +91,44 @@ describe("pattern", function () {
       expect(ir[7]).toBeNull();
     });
 
+    it("must bound the color component buffer while batching", function () {
+      const numComps = 32;
+      let batchStarts = 0;
+      let componentBufferLength = 0;
+      const colorSpace = [
+        Name.get("DeviceN"),
+        Array.from({ length: numComps }, (_, i) => Name.get(`Colorant${i}`)),
+        Name.get("DeviceRGB"),
+        {
+          fn(src, srcOffset, dest, destOffset) {
+            dest[destOffset] = src[srcOffset];
+            dest[destOffset + 1] = src[srcOffset + 1];
+            dest[destOffset + 2] = src[srcOffset + 2];
+          },
+        },
+      ];
+      const shading = createFunctionBasedShading({
+        colorSpace,
+        matrix: [64, 0, 0, 64, 0, 0],
+        fn(src, srcOffset, dest, destOffset) {
+          if (destOffset === 0) {
+            batchStarts++;
+            componentBufferLength = dest.length;
+          }
+          dest[destOffset] = src[srcOffset];
+          dest[destOffset + 1] = src[srcOffset + 1];
+          dest[destOffset + 2] = 0.5;
+          dest.fill(0, destOffset + 3, destOffset + numComps);
+        },
+      });
+      const [, , , colors] = shading.getIR();
+
+      const totalVertices = (64 + 1) ** 2;
+      expect(batchStarts).toBeGreaterThan(1);
+      expect(componentBufferLength).toBeLessThan(totalVertices * numComps);
+      expect(Array.from(colors.subarray(0, 4))).toEqual([0, 0, 128, 0]);
+    });
+
     it("must keep mesh colors intact through binary serialization", function () {
       const shading = createFunctionBasedShading({
         background: [0.25, 0.5, 0.75],