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fix: keep full alpha precision when parsing hex colors #137

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fix: keep full alpha precision when parsing hex colors #137

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5 changes: 3 additions & 2 deletions src/colorModels/hex.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
import { RgbaColor } from "../types";
import { round } from "../helpers";
import { ALPHA_PRECISION } from "../constants";
import { roundRgba } from "./rgb";

const hexMatcher = /^#([0-9a-f]{3,8})$/i;
Expand All @@ -17,7 +18,7 @@ export const parseHex = (hex: string): RgbaColor | null => {
r: parseInt(hex[0] + hex[0], 16),
g: parseInt(hex[1] + hex[1], 16),
b: parseInt(hex[2] + hex[2], 16),
a: hex.length === 4 ? round(parseInt(hex[3] + hex[3], 16) / 255, 2) : 1,
a: hex.length === 4 ? round(parseInt(hex[3] + hex[3], 16) / 255, ALPHA_PRECISION) : 1,
};
}

Expand All @@ -26,7 +27,7 @@ export const parseHex = (hex: string): RgbaColor | null => {
r: parseInt(hex.substr(0, 2), 16),
g: parseInt(hex.substr(2, 2), 16),
b: parseInt(hex.substr(4, 2), 16),
a: hex.length === 8 ? round(parseInt(hex.substr(6, 2), 16) / 255, 2) : 1,
a: hex.length === 8 ? round(parseInt(hex.substr(6, 2), 16) / 255, ALPHA_PRECISION) : 1,
};
}

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10 changes: 9 additions & 1 deletion tests/colord.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -56,14 +56,22 @@ it("Parses modern HSL functional notations", () => {

it("Supports HEX4 and HEX8 color models", () => {
expect(colord("#ffffffff").toRgb()).toMatchObject({ r: 255, g: 255, b: 255, a: 1 });
expect(colord("#80808080").toRgb()).toMatchObject({ r: 128, g: 128, b: 128, a: 0.5 });
expect(colord("#80808080").toRgb()).toMatchObject({ r: 128, g: 128, b: 128, a: 0.502 });
expect(colord("#AAAF").toRgb()).toMatchObject({ r: 170, g: 170, b: 170, a: 1 });
expect(colord("#5550").toRgb()).toMatchObject({ r: 85, g: 85, b: 85, a: 0 });
expect(colord({ r: 255, g: 255, b: 255, a: 1 }).toHex()).toBe("#ffffff");
expect(colord({ r: 170, g: 170, b: 170, a: 0.5 }).toHex()).toBe("#aaaaaa80");
expect(colord({ r: 128, g: 128, b: 128, a: 0 }).toHex()).toBe("#80808000");
});

it("Round-trips a HEX8 alpha channel without drifting", () => {
// The alpha byte of a HEX8 string is 8-bit; parsing must keep enough
// precision (ALPHA_PRECISION) to re-encode the very same byte.
["#476d5e55", "#80808080", "#0a141e7f", "#ffffff01", "#000000fe"].forEach((hex) => {
expect(colord(hex).toHex()).toBe(hex);
});
});

it("Ignores a case and extra whitespace", () => {
expect(colord(" #0a0a0a ").toRgb()).toMatchObject({ r: 10, g: 10, b: 10, a: 1 });
expect(colord("RGB( 10, 10, 10 )").toRgb()).toMatchObject({ r: 10, g: 10, b: 10, a: 1 });
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