feat: add instruments registry

web/src/lib/core/alpha.ts

@@ -1,4 +1,4 @@
-import type { PixelImage } from './types';
+import { createPixelImage, type PixelImage } from './types';
 
 const MAX_COLOR_DISTANCE = Math.sqrt(3 * 255 * 255);
 
@@ -22,6 +22,20 @@ export function removeColorToAlpha(
 	return out;
 }
 
+export function flattenOntoColor(img: PixelImage, hex: string): PixelImage {
+	const [bgR, bgG, bgB] = parseHex(hex);
+	const out = createPixelImage(img.width, img.height);
+	for (let i = 0; i < out.data.length; i += 4) {
+		const a = img.data[i + 3] / 255;
+		const inv = 1 - a;
+		out.data[i] = img.data[i] * a + bgR * inv;
+		out.data[i + 1] = img.data[i + 1] * a + bgG * inv;
+		out.data[i + 2] = img.data[i + 2] * a + bgB * inv;
+		out.data[i + 3] = 255;
+	}
+	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) {