Resize PNG resolution to avoid large files

bbb-export-annotations/config/settings.json

@@ -7,7 +7,7 @@
       "presAnnDropboxDir": "/tmp/pres-ann-dropbox"
     },
     "collector": {
-      "backgroundSlidePPI": 350
+      "pngWidthRasterizedSlides": 2048
     },
     "process": {
       "whiteboardTextEncoding": "utf-8",

bbb-export-annotations/workers/collector.js

@@ -70,14 +70,14 @@ let exportJob = JSON.parse(job);
         // CairoSVG doesn't handle transparent SVG and PNG embeds properly, e.g., in rasterized text.
         // So textboxes may get a black background when downloading/exporting repeatedly.
         // To avoid that, we take slides from the uploaded file, but later probe the dimensions from the SVG
-        // so it matches what was shown in the browser -- Tldraw unfortunately uses absolute coordinates.
+        // so it matches what was shown in the browser.
 
         let extract_png_from_pdf = [
           'pdftocairo',
           '-png',
           '-f', pageNumber, 
           '-l', pageNumber,
-          '-r', config.collector.backgroundSlidePPI,
+          '-scale-to', config.collector.pngWidthRasterizedSlides,
           '-singlefile',
           '-cropbox',
           pdfFile, outputFile,

bbb-export-annotations/workers/process.js

@@ -796,14 +796,12 @@ for (let currentSlide of pages) {
         if (err) { return logger.error(err); }
     });
 
-    // Dimensions converted back to a pixel size which,
+    // Dimensions converted to a pixel size which,
     // when converted to points, will yield the desired
     // dimension in pixels when read without conversion
 
-    // e.g. say Tldraw's canvas is 1920x1080 px.
-    // The background SVG dimensions are set to 1920x1080 pt (incorrect unit).
-    // So we read it in ignoring the unit as 1920x1080 px, making the position of the drawings match.
-    // Now we assume we had 1920x1080pt and resize to 2560x1440 px so that the SVG generates with the original "wrong" size.
+    // e.g. say the background SVG dimensions are set to 1920x1080 pt
+    // Resize output to 2560x1440 px so that the SVG generates with the original size in pt.
 
     let convertAnnotatedSlide = [
         'cairosvg',