Better approximate gradient color stops
PDF gradients do not have color stops but an arbitrary PDF function of the type f(t) -> color. CSS gradients are only based on color stops. Most PDF gradient functions are produced from color stop oriented gradients. Take advantage of this by sampling the PDF function at a higher frequency but not converting any samples which could be interpolated to color stops. The sampling frequency is chosen to be the least common multiple of as many values as practical to exactly re-create the common case of the PDF function implementing equally spaced linearly interpolated stops in RGB color space. This also allows for better approximation of other smooth PDF functions (non-linear, or non-equally spaced, or in different color space). Fixes: #10572, #14165
This commit is contained in:
Ben Wagner
parent
a0ef5a4ae1
commit
5fad91a680
@ -160,10 +160,9 @@ class RadialAxialShading extends BaseShading {
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const fnObj = dict.getRaw("Function");
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const fn = pdfFunctionFactory.createFromArray(fnObj);
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// 10 samples seems good enough for now, but probably won't work
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// if there are sharp color changes. Ideally, we would implement
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// the spec faithfully and add lossless optimizations.
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const NUMBER_OF_SAMPLES = 10;
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// Use lcm(1,2,3,4,5,6,7,8,10) = 840 (including 9 increases this to 2520)
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// to catch evenly spaced stops. oeis.org/A003418
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const NUMBER_OF_SAMPLES = 840;
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const step = (t1 - t0) / NUMBER_OF_SAMPLES;
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const colorStops = (this.colorStops = []);
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@ -179,13 +178,80 @@ class RadialAxialShading extends BaseShading {
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const color = new Float32Array(cs.numComps),
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ratio = new Float32Array(1);
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let rgbColor;
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for (let i = 0; i <= NUMBER_OF_SAMPLES; i++) {
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let iBase = 0;
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ratio[0] = t0;
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fn(ratio, 0, color, 0);
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let rgbBase = cs.getRgb(color, 0);
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const cssColorBase = Util.makeHexColor(rgbBase[0], rgbBase[1], rgbBase[2]);
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colorStops.push([0, cssColorBase]);
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let iPrev = 1;
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ratio[0] = t0 + step;
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fn(ratio, 0, color, 0);
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let rgbPrev = cs.getRgb(color, 0);
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// Slopes are rise / run.
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// A max slope is from the least value the base component could have been
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// to the greatest value the current component could have been.
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// A min slope is from the greatest value the base component could have been
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// to the least value the current component could have been.
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// Each component could have been rounded up to .5 from its original value
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// so the conservative deltas are +-1 (+-.5 for base and -+.5 for current).
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// The run is iPrev - iBase = 1, so omitted.
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let maxSlopeR = rgbPrev[0] - rgbBase[0] + 1;
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let maxSlopeG = rgbPrev[1] - rgbBase[1] + 1;
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let maxSlopeB = rgbPrev[2] - rgbBase[2] + 1;
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let minSlopeR = rgbPrev[0] - rgbBase[0] - 1;
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let minSlopeG = rgbPrev[1] - rgbBase[1] - 1;
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let minSlopeB = rgbPrev[2] - rgbBase[2] - 1;
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for (let i = 2; i < NUMBER_OF_SAMPLES; i++) {
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ratio[0] = t0 + i * step;
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fn(ratio, 0, color, 0);
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rgbColor = cs.getRgb(color, 0);
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const cssColor = Util.makeHexColor(rgbColor[0], rgbColor[1], rgbColor[2]);
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colorStops.push([i / NUMBER_OF_SAMPLES, cssColor]);
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// Keep going if the maximum minimum slope <= the minimum maximum slope.
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// Otherwise add a rgbPrev color stop and make it the new base.
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const run = i - iBase;
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maxSlopeR = Math.min(maxSlopeR, (rgbColor[0] - rgbBase[0] + 1) / run);
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maxSlopeG = Math.min(maxSlopeG, (rgbColor[1] - rgbBase[1] + 1) / run);
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maxSlopeB = Math.min(maxSlopeB, (rgbColor[2] - rgbBase[2] + 1) / run);
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minSlopeR = Math.max(minSlopeR, (rgbColor[0] - rgbBase[0] - 1) / run);
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minSlopeG = Math.max(minSlopeG, (rgbColor[1] - rgbBase[1] - 1) / run);
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minSlopeB = Math.max(minSlopeB, (rgbColor[2] - rgbBase[2] - 1) / run);
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const slopesExist =
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minSlopeR <= maxSlopeR &&
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minSlopeG <= maxSlopeG &&
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minSlopeB <= maxSlopeB;
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if (!slopesExist) {
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const cssColor = Util.makeHexColor(rgbPrev[0], rgbPrev[1], rgbPrev[2]);
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colorStops.push([iPrev / NUMBER_OF_SAMPLES, cssColor]);
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// TODO: When fn frequency is high (iPrev - iBase === 1 twice in a row),
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// send the color space and function to do the sampling display side.
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// The run is i - iPrev = 1, so omitted.
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maxSlopeR = rgbColor[0] - rgbPrev[0] + 1;
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maxSlopeG = rgbColor[1] - rgbPrev[1] + 1;
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maxSlopeB = rgbColor[2] - rgbPrev[2] + 1;
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minSlopeR = rgbColor[0] - rgbPrev[0] - 1;
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minSlopeG = rgbColor[1] - rgbPrev[1] - 1;
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minSlopeB = rgbColor[2] - rgbPrev[2] - 1;
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iBase = iPrev;
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rgbBase = rgbPrev;
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}
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iPrev = i;
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rgbPrev = rgbColor;
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}
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const cssColor = Util.makeHexColor(rgbPrev[0], rgbPrev[1], rgbPrev[2]);
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colorStops.push([1, cssColor]);
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let background = "transparent";
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if (dict.has("Background")) {
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2
test/pdfs/.gitignore
vendored
2
test/pdfs/.gitignore
vendored
@ -341,6 +341,7 @@
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!issue12810.pdf
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!bug866395.pdf
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!issue12010_reduced.pdf
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!issue10572.pdf
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!issue11718_reduced.pdf
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!bug1027533.pdf
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!bug1028735.pdf
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@ -529,6 +530,7 @@
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!issue15012.pdf
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!issue15150.pdf
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!poppler-395-0-fuzzed.pdf
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!issue14165.pdf
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!GHOSTSCRIPT-698804-1-fuzzed.pdf
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!issue14814.pdf
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!poppler-91414-0-53.pdf
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374
test/pdfs/issue10572.pdf
Normal file
374
test/pdfs/issue10572.pdf
Normal file
@ -0,0 +1,374 @@
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xref
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startxref
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3146
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%%EOF
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336
test/pdfs/issue14165.pdf
Normal file
336
test/pdfs/issue14165.pdf
Normal file
File diff suppressed because one or more lines are too long
@ -5376,6 +5376,12 @@
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"enableXfa": true,
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"type": "eq"
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},
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{ "id": "issue14165",
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@ -6251,6 +6257,12 @@
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}
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}
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},
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{ "id": "issue10572",
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{ "id": "issue11931",
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"md5": "9ea233037992e1f10280420a49e72845",
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