feat: core instruments

web/src/lib/core/alpha.ts

@@ -0,0 +1,47 @@
+import type { PixelImage } from './types';
+
+const MAX_COLOR_DISTANCE = Math.sqrt(3 * 255 * 255);
+
+export function removeColorToAlpha(
+	img: PixelImage,
+	hex: string,
+	tolerancePercent = 0
+): PixelImage {
+	const [targetR, targetG, targetB] = parseHex(hex);
+	const tolerance = (clamp(tolerancePercent, 0, 100) / 100) * MAX_COLOR_DISTANCE;
+	const thresholdSq = tolerance * tolerance;
+	const out: PixelImage = { width: img.width, height: img.height, data: img.data.slice() };
+	for (let i = 0; i < out.data.length; i += 4) {
+		const dr = out.data[i] - targetR;
+		const dg = out.data[i + 1] - targetG;
+		const db = out.data[i + 2] - targetB;
+		if (dr * dr + dg * dg + db * db <= thresholdSq) {
+			out.data[i + 3] = 0;
+		}
+	}
+	return out;
+}
+
+export function parseHex(hex: string): [number, number, number] {
+	const match = /^#?([0-9a-f]{3}|[0-9a-f]{6})$/i.exec(hex.trim());
+	if (!match) {
+		throw new Error(`Некорректный HEX-цвет: "${hex}"`);
+	}
+	const digits = match[1];
+	if (digits.length === 3) {
+		return [
+			parseInt(digits[0] + digits[0], 16),
+			parseInt(digits[1] + digits[1], 16),
+			parseInt(digits[2] + digits[2], 16)
+		];
+	}
+	return [
+		parseInt(digits.slice(0, 2), 16),
+		parseInt(digits.slice(2, 4), 16),
+		parseInt(digits.slice(4, 6), 16)
+	];
+}
+
+function clamp(value: number, min: number, max: number): number {
+	return Math.min(max, Math.max(min, value));
+}