than_pdf_engine

than_pdf_engine is a high-performance C++ native wrapper class designed for rendering and processing PDF documents. This engine acts as a low-level bridge, wrapping the capabilities of Foxit's Pdfium engine through pdfium_dart to provide optimal execution speed and efficient memory management.

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🚀 Overview

When building applications that handle high-volume or heavy PDF files, processing speed and memory safety are critical. than_pdf_engine is written in C++ to bypass high-level overhead, directly leveraging native binaries while providing a clean, abstract interface for your application layer.

[ Your Application / Dart Layer ]
│
▼ (Dart FFI)
┌──────────────────────────────────────┐
│          than_pdf_engine             │  <-- This Wrapper Project
│     (C++ Native Wrapper Class)       │
└─────────────────┬────────────────────┘
│
▼
[ pdfium_dart Core Lib ]

Pdfium lib native wrapper class.witten by c++.

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📦 Dependencies

To integrate and build this native engine, you need to add the core Pdfium binding library into your project's dependencies.

Add the following block to your pubspec.yaml file:

dependencies:
  pdfium_dart: ^latest

Avaliable

• x PdfThumbnailGenerator
• x PdfCore
• x PdfBackgroundWorker

Basic PDF Operations

• You can use the high-level PdfCore API to quickly extract page sizes or generate image thumbnails from a PDF file.

// Get list of sizes for all pages
final pageSizes = await PdfCore.getAllPageSizedList('/home/thancoder/Documents/test3.pdf');

// PdfThumbnailGenerator
final g = PdfThumbnailGenerator.instance;
final success = await g.generate(pdfPath, outPath,
    pageIndex: 0,//default
    overrideImage: false,//default
    password: null,
    quality: 80,//default
    height: 0,//original height
    width: 0, //original width
    type: PdfThumbnailGeneratorImageType //jpg,png
);

// Generate a JPG thumbnail
await PdfCore.genThumbnailJpg(
    "/home/thancoder/Documents/test3.pdf",
    'test3.jpg',
);

// Generate a PNG thumbnail
await PdfCore.genThumbnailPng(
    "/home/thancoder/Documents/test3.pdf",
    'test3.png',
);

PdfThumbnailGenerator Example

• Auto Close Thread

final g = PdfThumbnailGenerator.instance;
final dir = Directory('/home/thancoder/Documents/pdf');
final outDir = Directory('${dir.path}/thumbnails');
if (!outDir.existsSync()) {
    outDir.createSync(recursive: false);
}
for (var file in dir.listSync(followLinks: false)) {
    final name = file.path.split('/').last.split('.').first;
    print('$name: Starting...');

    final res = await g.generate(
    file.path,
    '${outDir.path}/$name.jpg',
    overrideImage: true,
    height: 200,
    width: 200,
    );
    print('$name: $res');
}
//[PdfThumbnailGenerator:_intiIsolate]: start background isolate]

//your task
// i will wait `5s`
//[PdfThumbnailGenerator:_killIsolate]: close background isolate

Using Background PDF Worker (Isolate-based)

• For heavy rendering pipelines, use PdfBackgroundWorker to offload tasks to a separate Dart Isolate. This keeps your main UI thread smooth and responsive.

// Get the singleton instance of Background Worker
final pdfWorker = PdfBackgroundWorker.getInstance;

// Initialize the worker with the target PDF file
await pdfWorker.run('/home/thancoder/Documents/test3.pdf');

/// pdf -> `width,height` list
final (pageSizeList, error) = await PdfCore.getAllPageSizedList(widget.path);

// Request a specific page as a JPG image asynchronously
final WorkerImageResponse? res = await pdfWorker.requestPageImageJpg(
      0, //pageIndex
      width: 0,//original
      height: 0, //original
      quality: 70,
    );
// use iamge
final image = Uint8List.fromList(res.trans.materialize().asUint8List());

// Clean up and release worker resources when done
await pdfWorker.dispose();

Native Low-Level API (C++ Bindings via FFI)

• If you need direct, low-level access to the underlying C++ wrapper functions, you can invoke them directly using Dart FFI pointers.

import 'dart:ffi';
import 'package:ffi/ffi.dart';
import 'package:than_pdf_engine/than_pdf_engine.dart';
import 'package:than_pdf_engine/than_pdf_engine_bindings_generated.dart';

// Create the native PDF core instance
final pdf = pdf_core_create();
final pathPtr = "/home/thancoder/Documents/test3.pdf".toNativeUtf8();

// Open the PDF file at the native level
pdf_core_openFile(pdf, pathPtr.cast<Char>(), nullptr);

// Retrieve total page count
final pageCount = pdf_core_getPageCount(pdf);
print('Total Pages: $pageCount');

// Strictly manage memory: Destroy engine instance and free pointers
pdf_core_destroy(pdf);
calloc.free(pathPtr);