Dither badge photos before drawing them

src/printer.js

@@ -6,6 +6,7 @@ import { execFile } from 'node:child_process';
 import { createCanvas, loadImage, GlobalFonts } from '@napi-rs/canvas';
 import config from './config.js';
 import { photoAbsolutePath } from './photos.js';
+import { ditherPhoto } from './printing/dither.js';
 import { printPng, printerHealth } from './printing/ql-print.js';
 
 /**
@@ -114,6 +115,17 @@ async function drawBadge(ctx, widthDots, heightDots, visit, site, accent, startY
   }
 
   const photoSize = photo ? Math.round(unit * (portrait ? 0.52 : 0.5)) : 0;
+
+  // Thermal heads print pure black or nothing, so a photo has to be reduced to
+  // 1-bit before it lands on the canvas — otherwise the plane conversion
+  // thresholds it into a solid blob. Done once here rather than at each draw
+  // site, and at exactly photoSize: rescaling a dithered image resamples the
+  // dot pattern back into greys and undoes the whole thing.
+  //
+  // Skipped on the measuring pass, which never paints.
+  if (photo && photoSize > 0 && startY !== null) {
+    photo = ditherPhoto(photo, photoSize);
+  }
   let cursorY = startY === null ? pad : startY;
   let textLeft = pad;
   let textWidth = widthDots - pad * 2;