Supersample OG PNGs: render at 3x then downsample to 1200x630

Renders SVG at 3600×1890 via Batik, then downsamples to 1200×630
using bicubic interpolation for crisp anti-aliased text at the
exact OG-recommended dimensions.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: brunoborges

html-generators/generateog.java

@@ -132,14 +132,27 @@ static void ensureFonts() throws IOException {
 }
 
 /** Convert an SVG string to a PNG file using Batik. */
+/** Convert SVG to a crisp 1200×630 PNG by rendering at 3× then downsampling with bicubic interpolation. */
 static void svgToPng(String svgContent, Path pngPath) throws Exception {
+    int scale = 3;
+    // Render at 3× resolution
     var input = new TranscoderInput(new java.io.StringReader(svgContent));
-    try (var out = new java.io.BufferedOutputStream(Files.newOutputStream(pngPath))) {
-        var transcoder = new PNGTranscoder();
-        transcoder.addTranscodingHint(PNGTranscoder.KEY_WIDTH, (float) W * 2);
-        transcoder.addTranscodingHint(PNGTranscoder.KEY_HEIGHT, (float) H * 2);
-        transcoder.transcode(input, new TranscoderOutput(out));
-    }
+    var bos = new java.io.ByteArrayOutputStream();
+    var transcoder = new PNGTranscoder();
+    transcoder.addTranscodingHint(PNGTranscoder.KEY_WIDTH, (float) (W * scale));
+    transcoder.addTranscodingHint(PNGTranscoder.KEY_HEIGHT, (float) (H * scale));
+    transcoder.transcode(input, new TranscoderOutput(bos));
+
+    // Read back and downsample to 1200×630
+    var hiRes = javax.imageio.ImageIO.read(new java.io.ByteArrayInputStream(bos.toByteArray()));
+    var target = new java.awt.image.BufferedImage(W, H, java.awt.image.BufferedImage.TYPE_INT_ARGB);
+    var g = target.createGraphics();
+    g.setRenderingHint(java.awt.RenderingHints.KEY_INTERPOLATION, java.awt.RenderingHints.VALUE_INTERPOLATION_BICUBIC);
+    g.setRenderingHint(java.awt.RenderingHints.KEY_RENDERING, java.awt.RenderingHints.VALUE_RENDER_QUALITY);
+    g.setRenderingHint(java.awt.RenderingHints.KEY_ANTIALIASING, java.awt.RenderingHints.VALUE_ANTIALIAS_ON);
+    g.drawImage(hiRes, 0, 0, W, H, null);
+    g.dispose();
+    javax.imageio.ImageIO.write(target, "png", pngPath.toFile());
 }
 
 static SequencedMap<String, String> loadProperties(String file) {