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Merge pull request #16106 from bungeman/improve_color_stop_detection

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Better approximate gradient color stops
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calixteman 2023-05-04 19:48:57 +02:00 • committed by GitHub
commit a24e11a91c
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5 changed files with 797 additions and 7 deletions
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src/core/pattern.js
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@ -157,10 +157,9 @@ class RadialAxialShading extends BaseShading {
const fnObj = dict.getRaw("Function");
const fn = pdfFunctionFactory.createFromArray(fnObj);
// 10 samples seems good enough for now, but probably won't work
// if there are sharp color changes. Ideally, we would implement
// the spec faithfully and add lossless optimizations.
const NUMBER_OF_SAMPLES = 10;
// Use lcm(1,2,3,4,5,6,7,8,10) = 840 (including 9 increases this to 2520)
// to catch evenly spaced stops. oeis.org/A003418
const NUMBER_OF_SAMPLES = 840;
const step = (t1 - t0) / NUMBER_OF_SAMPLES;
const colorStops = (this.colorStops = []);
@ -176,13 +175,80 @@ class RadialAxialShading extends BaseShading {
const color = new Float32Array(cs.numComps),
ratio = new Float32Array(1);
let rgbColor;
for (let i = 0; i <= NUMBER_OF_SAMPLES; i++) {
let iBase = 0;
ratio[0] = t0;
fn(ratio, 0, color, 0);
let rgbBase = cs.getRgb(color, 0);
const cssColorBase = Util.makeHexColor(rgbBase[0], rgbBase[1], rgbBase[2]);
colorStops.push([0, cssColorBase]);
let iPrev = 1;
ratio[0] = t0 + step;
fn(ratio, 0, color, 0);
let rgbPrev = cs.getRgb(color, 0);
// Slopes are rise / run.
// A max slope is from the least value the base component could have been
// to the greatest value the current component could have been.
// A min slope is from the greatest value the base component could have been
// to the least value the current component could have been.
// Each component could have been rounded up to .5 from its original value
// so the conservative deltas are +-1 (+-.5 for base and -+.5 for current).
// The run is iPrev - iBase = 1, so omitted.
let maxSlopeR = rgbPrev[0] - rgbBase[0] + 1;
let maxSlopeG = rgbPrev[1] - rgbBase[1] + 1;
let maxSlopeB = rgbPrev[2] - rgbBase[2] + 1;
let minSlopeR = rgbPrev[0] - rgbBase[0] - 1;
let minSlopeG = rgbPrev[1] - rgbBase[1] - 1;
let minSlopeB = rgbPrev[2] - rgbBase[2] - 1;
for (let i = 2; i < NUMBER_OF_SAMPLES; i++) {
ratio[0] = t0 + i * step;
fn(ratio, 0, color, 0);
rgbColor = cs.getRgb(color, 0);
const cssColor = Util.makeHexColor(rgbColor[0], rgbColor[1], rgbColor[2]);
colorStops.push([i / NUMBER_OF_SAMPLES, cssColor]);
// Keep going if the maximum minimum slope <= the minimum maximum slope.
// Otherwise add a rgbPrev color stop and make it the new base.
const run = i - iBase;
maxSlopeR = Math.min(maxSlopeR, (rgbColor[0] - rgbBase[0] + 1) / run);
maxSlopeG = Math.min(maxSlopeG, (rgbColor[1] - rgbBase[1] + 1) / run);
maxSlopeB = Math.min(maxSlopeB, (rgbColor[2] - rgbBase[2] + 1) / run);
minSlopeR = Math.max(minSlopeR, (rgbColor[0] - rgbBase[0] - 1) / run);
minSlopeG = Math.max(minSlopeG, (rgbColor[1] - rgbBase[1] - 1) / run);
minSlopeB = Math.max(minSlopeB, (rgbColor[2] - rgbBase[2] - 1) / run);
const slopesExist =
minSlopeR <= maxSlopeR &&
minSlopeG <= maxSlopeG &&
minSlopeB <= maxSlopeB;
if (!slopesExist) {
const cssColor = Util.makeHexColor(rgbPrev[0], rgbPrev[1], rgbPrev[2]);
colorStops.push([iPrev / NUMBER_OF_SAMPLES, cssColor]);
// TODO: When fn frequency is high (iPrev - iBase === 1 twice in a row),
// send the color space and function to do the sampling display side.
// The run is i - iPrev = 1, so omitted.
maxSlopeR = rgbColor[0] - rgbPrev[0] + 1;
maxSlopeG = rgbColor[1] - rgbPrev[1] + 1;
maxSlopeB = rgbColor[2] - rgbPrev[2] + 1;
minSlopeR = rgbColor[0] - rgbPrev[0] - 1;
minSlopeG = rgbColor[1] - rgbPrev[1] - 1;
minSlopeB = rgbColor[2] - rgbPrev[2] - 1;
iBase = iPrev;
rgbBase = rgbPrev;
}
iPrev = i;
rgbPrev = rgbColor;
}
const cssColor = Util.makeHexColor(rgbPrev[0], rgbPrev[1], rgbPrev[2]);
colorStops.push([1, cssColor]);
let background = "transparent";
if (dict.has("Background")) {