[feature] Use blurhashes in frontend, tidy up gallery view a bit

web/source/blurhash/index.js

@@ -0,0 +1,66 @@
+/*
+	GoToSocial
+	Copyright (C) GoToSocial Authors admin@gotosocial.org
+	SPDX-License-Identifier: AGPL-3.0-or-later
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU Affero General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU Affero General Public License for more details.
+
+	You should have received a copy of the GNU Affero General Public License
+	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+import { decode } from "blurhash";
+
+Array.from(document.getElementsByClassName('blurhash-container')).forEach(blurhashContainer => {
+	const hash = blurhashContainer.dataset.blurhashHash;
+	const thumbHeight = blurhashContainer.dataset.blurhashHeight;
+	const thumbWidth = blurhashContainer.dataset.blurhashWidth;
+	const thumbAspect = blurhashContainer.dataset.blurhashAspect;	
+	
+	/*
+		It's very expensive to draw big canvases
+		with blurhashes, so use tiny ones, keeping
+		aspect ratio of the original thumbnail.
+	*/
+	var useWidth = 32;
+	var useHeight = 32;
+	switch (true) {
+		case thumbWidth > thumbHeight:
+			useHeight = Math.round(useWidth / thumbAspect);
+			break;
+		case thumbHeight > thumbWidth:
+			useWidth = Math.round(useHeight * thumbAspect);
+			break;
+	}
+
+	const pixels = decode(
+		hash,
+		useWidth,
+		useHeight,
+	);
+
+	// Create canvas of appropriate size.
+	const canvas = document.createElement("canvas");
+	canvas.width = useWidth;
+	canvas.height = useHeight;
+
+	// Draw the image data into the canvas.
+	const ctx = canvas.getContext("2d");
+	const imageData = ctx.createImageData(
+		useWidth,
+		useHeight,
+	);
+	imageData.data.set(pixels);
+	ctx.putImageData(imageData, 0, 0);
+
+	// Put the canvas inside the container.
+	blurhashContainer.appendChild(canvas);
+});