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pdf_signature
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fix: image background remove function

This commit is contained in:
insleker 2025-08-29 16:53:06 +08:00
parent 5990f6fb01
commit 828eee49e2
9 changed files with 320 additions and 130 deletions
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8
docs/FRs.md
View File

@ -26,3 +26,11 @@
* role: user
* functionality: save/export the signed PDF document
* benefit: easily keep a copy of the signed document for records.
* name: preferences for app
* role: user
* functionality: configure app preferences such as `theme`, `language`.
* benefit: customize the app experience to better fit user needs
* name: remember preferences
* role: user
* functionality: remember user preferences for future sessions
* benefit: provide a consistent and personalized experience

18
lib/data/services/export_service.dart
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@ -160,10 +160,20 @@ class ExportService {
signatureImageBytes.isNotEmpty;
if (shouldStamp) {
try {
final decoded = img.decodeImage(signatureImageBytes);
if (decoded != null) {
final jpg = img.encodeJpg(decoded, quality: 90);
sigImgObj = pw.MemoryImage(Uint8List.fromList(jpg));
// If it's already PNG, keep as-is to preserve alpha; otherwise decode/encode PNG
final asStr = String.fromCharCodes(signatureImageBytes.take(8));
final isPng =
signatureImageBytes.length > 8 &&
signatureImageBytes[0] == 0x89 &&
asStr.startsWith('\u0089PNG');
if (isPng) {
sigImgObj = pw.MemoryImage(signatureImageBytes);
} else {
final decoded = img.decodeImage(signatureImageBytes);
if (decoded != null) {
final png = img.encodePng(decoded, level: 6);
sigImgObj = pw.MemoryImage(Uint8List.fromList(png));
}
}
} catch (_) {}
}

3
lib/data/services/providers.dart
View File

@ -17,6 +17,9 @@ final exportDpiProvider = StateProvider<double>((_) => 144.0);
// Controls whether signature overlay is visible (used to hide on non-stamped pages during export)
final signatureVisibilityProvider = StateProvider<bool>((_) => true);
// Global exporting state to show loading UI and block interactions while saving/exporting
final exportingProvider = StateProvider<bool>((_) => false);
// Save path picker (injected for tests)
final savePathPickerProvider = Provider<Future<String?> Function()>((ref) {
return () async {

72
lib/ui/features/pdf/view_model/view_model.dart
View File

@ -2,6 +2,7 @@ import 'dart:math' as math;
import 'dart:typed_data';
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:image/image.dart' as img;
import '../../../../data/model/model.dart';
@ -192,3 +193,74 @@ final signatureProvider =
StateNotifierProvider<SignatureController, SignatureState>(
(ref) => SignatureController(),
);
/// Derived provider that returns processed signature image bytes according to
/// current adjustment settings (contrast/brightness) and background removal.
/// Returns null if no image is loaded. The output is a PNG to preserve alpha.
final processedSignatureImageProvider = Provider<Uint8List?>((ref) {
final s = ref.watch(signatureProvider);
final bytes = s.imageBytes;
if (bytes == null || bytes.isEmpty) return null;
// Decode (supports PNG/JPEG, etc.)
final decoded = img.decodeImage(bytes);
if (decoded == null) return bytes;
// Work on a copy and ensure an alpha channel is present (RGBA)
var out = decoded.clone();
if (out.hasPalette || !out.hasAlpha) {
// Force truecolor RGBA image so per-pixel alpha writes take effect
out = out.convert(numChannels: 4);
}
// Parameters
final double contrast = s.contrast; // [0..2], 1 = neutral
final double brightness = s.brightness; // [-1..1], 0 = neutral
const int thrLow = 220; // begin soft transparency from this avg luminance
const int thrHigh = 245; // fully transparent from this avg luminance
// Helper to clamp int
int _clamp255(num v) => v.clamp(0, 255).toInt();
// Iterate pixels
for (int y = 0; y < out.height; y++) {
for (int x = 0; x < out.width; x++) {
final p = out.getPixel(x, y);
int a = _clamp255(p.aNormalized * 255.0);
int r = _clamp255(p.rNormalized * 255.0);
int g = _clamp255(p.gNormalized * 255.0);
int b = _clamp255(p.bNormalized * 255.0);
// Apply contrast/brightness in sRGB space
// new = (old-128)*contrast + 128 + brightness*255
final double brOffset = brightness * 255.0;
r = _clamp255((r - 128) * contrast + 128 + brOffset);
g = _clamp255((g - 128) * contrast + 128 + brOffset);
b = _clamp255((b - 128) * contrast + 128 + brOffset);
// Near-white background removal (compute average luminance)
final int avg = ((r + g + b) / 3).round();
int remAlpha = 255; // 255 = fully opaque, 0 = transparent
if (s.bgRemoval) {
if (avg >= thrHigh) {
remAlpha = 0;
} else if (avg >= thrLow) {
// Soft fade between thrLow..thrHigh
final double t = (avg - thrLow) / (thrHigh - thrLow);
remAlpha = _clamp255(255 * (1.0 - t));
} else {
remAlpha = 255;
}
}
// Combine with existing alpha (preserve existing transparency)
final newA = math.min(a, remAlpha);
out.setPixelRgba(x, y, r, g, b, newA);
}
}
// Encode as PNG to preserve transparency
final png = img.encodePng(out, level: 6);
return Uint8List.fromList(png);
});

311
lib/ui/features/pdf/widgets/pdf_screen.dart
View File

@ -91,116 +91,129 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
}
Future<void> _saveSignedPdf() async {
final pdf = ref.read(pdfProvider);
final sig = ref.read(signatureProvider);
// Cache messenger before any awaits to avoid using BuildContext across async gaps.
final messenger = ScaffoldMessenger.of(context);
if (!pdf.loaded || sig.rect == null) {
messenger.showSnackBar(
const SnackBar(
content: Text('Nothing to save yet'),
), // guard per use-case
);
return;
}
final exporter = ref.read(exportServiceProvider);
final targetDpi = ref.read(exportDpiProvider);
final useMock = ref.read(useMockViewerProvider);
bool ok = false;
String? savedPath;
if (kIsWeb) {
// Web: prefer using picked bytes; share via Printing
Uint8List? src = pdf.pickedPdfBytes;
if (src == null) {
ok = false;
} else {
final bytes = await exporter.exportSignedPdfFromBytes(
srcBytes: src,
signedPage: pdf.signedPage,
signatureRectUi: sig.rect,
uiPageSize: SignatureController.pageSize,
signatureImageBytes: sig.imageBytes,
targetDpi: targetDpi,
// Set exporting state to show loading overlay and block interactions
ref.read(exportingProvider.notifier).state = true;
try {
final pdf = ref.read(pdfProvider);
final sig = ref.read(signatureProvider);
// Cache messenger before any awaits to avoid using BuildContext across async gaps.
final messenger = ScaffoldMessenger.of(context);
if (!pdf.loaded || sig.rect == null) {
messenger.showSnackBar(
const SnackBar(
content: Text('Nothing to save yet'),
), // guard per use-case
);
if (bytes != null) {
try {
await printing.Printing.sharePdf(
bytes: bytes,
filename: 'signed.pdf',
);
ok = true;
} catch (_) {
return;
}
final exporter = ref.read(exportServiceProvider);
final targetDpi = ref.read(exportDpiProvider);
final useMock = ref.read(useMockViewerProvider);
bool ok = false;
String? savedPath;
if (kIsWeb) {
// Web: prefer using picked bytes; share via Printing
Uint8List? src = pdf.pickedPdfBytes;
if (src == null) {
ok = false;
} else {
final processed = ref.read(processedSignatureImageProvider);
final bytes = await exporter.exportSignedPdfFromBytes(
srcBytes: src,
signedPage: pdf.signedPage,
signatureRectUi: sig.rect,
uiPageSize: SignatureController.pageSize,
signatureImageBytes: processed ?? sig.imageBytes,
targetDpi: targetDpi,
);
if (bytes != null) {
try {
await printing.Printing.sharePdf(
bytes: bytes,
filename: 'signed.pdf',
);
ok = true;
} catch (_) {
ok = false;
}
} else {
ok = false;
}
}
} else {
// Desktop/mobile: choose between bytes or file-based export
final pick = ref.read(savePathPickerProvider);
final path = await pick();
if (path == null || path.trim().isEmpty) return;
final fullPath = _ensurePdfExtension(path.trim());
savedPath = fullPath;
if (pdf.pickedPdfBytes != null) {
final processed = ref.read(processedSignatureImageProvider);
final out = await exporter.exportSignedPdfFromBytes(
srcBytes: pdf.pickedPdfBytes!,
signedPage: pdf.signedPage,
signatureRectUi: sig.rect,
uiPageSize: SignatureController.pageSize,
signatureImageBytes: processed ?? sig.imageBytes,
targetDpi: targetDpi,
);
if (useMock) {
// In mock mode for tests, simulate success without file IO
ok = out != null;
} else if (out != null) {
ok = await exporter.saveBytesToFile(
bytes: out,
outputPath: fullPath,
);
} else {
ok = false;
}
} else if (pdf.pickedPdfPath != null) {
if (useMock) {
// Simulate success in mock
ok = true;
} else {
final processed = ref.read(processedSignatureImageProvider);
ok = await exporter.exportSignedPdfFromFile(
inputPath: pdf.pickedPdfPath!,
outputPath: fullPath,
signedPage: pdf.signedPage,
signatureRectUi: sig.rect,
uiPageSize: SignatureController.pageSize,
signatureImageBytes: processed ?? sig.imageBytes,
targetDpi: targetDpi,
);
}
} else {
ok = false;
}
}
} else {
// Desktop/mobile: choose between bytes or file-based export
final pick = ref.read(savePathPickerProvider);
final path = await pick();
if (path == null || path.trim().isEmpty) return;
final fullPath = _ensurePdfExtension(path.trim());
savedPath = fullPath;
if (pdf.pickedPdfBytes != null) {
final out = await exporter.exportSignedPdfFromBytes(
srcBytes: pdf.pickedPdfBytes!,
signedPage: pdf.signedPage,
signatureRectUi: sig.rect,
uiPageSize: SignatureController.pageSize,
signatureImageBytes: sig.imageBytes,
targetDpi: targetDpi,
);
if (useMock) {
// In mock mode for tests, simulate success without file IO
ok = out != null;
} else if (out != null) {
ok = await exporter.saveBytesToFile(bytes: out, outputPath: fullPath);
if (!kIsWeb) {
// Desktop/mobile: we had a concrete path
if (ok) {
messenger.showSnackBar(
SnackBar(content: Text('Saved: ${savedPath ?? ''}')),
);
} else {
ok = false;
}
} else if (pdf.pickedPdfPath != null) {
if (useMock) {
// Simulate success in mock
ok = true;
} else {
ok = await exporter.exportSignedPdfFromFile(
inputPath: pdf.pickedPdfPath!,
outputPath: fullPath,
signedPage: pdf.signedPage,
signatureRectUi: sig.rect,
uiPageSize: SignatureController.pageSize,
signatureImageBytes: sig.imageBytes,
targetDpi: targetDpi,
messenger.showSnackBar(
const SnackBar(content: Text('Failed to save PDF')),
);
}
} else {
ok = false;
}
}
if (!kIsWeb) {
// Desktop/mobile: we had a concrete path
if (ok) {
messenger.showSnackBar(
SnackBar(content: Text('Saved: ${savedPath ?? ''}')),
);
} else {
messenger.showSnackBar(
const SnackBar(content: Text('Failed to save PDF')),
);
}
} else {
// Web: indicate whether we triggered a download dialog
if (ok) {
messenger.showSnackBar(
const SnackBar(content: Text('Download started')),
);
} else {
messenger.showSnackBar(
const SnackBar(content: Text('Failed to generate PDF')),
);
// Web: indicate whether we triggered a download dialog
if (ok) {
messenger.showSnackBar(
const SnackBar(content: Text('Download started')),
);
} else {
messenger.showSnackBar(
const SnackBar(content: Text('Failed to generate PDF')),
);
}
}
} finally {
// Clear exporting state when finished or on error
ref.read(exportingProvider.notifier).state = false;
}
}
@ -212,30 +225,62 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
@override
Widget build(BuildContext context) {
final pdf = ref.watch(pdfProvider);
final isExporting = ref.watch(exportingProvider);
return Scaffold(
appBar: AppBar(title: const Text('PDF Signature')),
body: Padding(
padding: const EdgeInsets.all(12),
child: Column(
child: Stack(
children: [
_buildToolbar(pdf),
const SizedBox(height: 8),
Expanded(child: _buildPageArea(pdf)),
Consumer(
builder: (context, ref, _) {
final sig = ref.watch(signatureProvider);
return sig.rect != null
? _buildAdjustmentsPanel(sig)
: const SizedBox.shrink();
},
Column(
children: [
_buildToolbar(pdf, disabled: isExporting),
const SizedBox(height: 8),
Expanded(
child: AbsorbPointer(
absorbing: isExporting,
child: _buildPageArea(pdf),
),
),
Consumer(
builder: (context, ref, _) {
final sig = ref.watch(signatureProvider);
return sig.rect != null
? AbsorbPointer(
absorbing: isExporting,
child: _buildAdjustmentsPanel(sig),
)
: const SizedBox.shrink();
},
),
],
),
if (isExporting)
Positioned.fill(
child: Container(
color: Colors.black45,
child: const Center(
child: Column(
mainAxisSize: MainAxisSize.min,
children: [
CircularProgressIndicator(),
SizedBox(height: 12),
Text(
'Exporting... Please wait',
style: TextStyle(color: Colors.white),
),
],
),
),
),
),
],
),
),
);
}
Widget _buildToolbar(PdfState pdf) {
Widget _buildToolbar(PdfState pdf, {bool disabled = false}) {
final dpi = ref.watch(exportDpiProvider);
final pageInfo = 'Page ${pdf.currentPage}/${pdf.pageCount}';
return Wrap(
@ -245,7 +290,7 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
children: [
OutlinedButton(
key: const Key('btn_open_pdf_picker'),
onPressed: _pickPdf,
onPressed: disabled ? null : _pickPdf,
child: const Text('Open PDF...'),
),
if (pdf.loaded) ...[
@ -254,14 +299,16 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
children: [
IconButton(
key: const Key('btn_prev'),
onPressed: () => _jumpToPage(pdf.currentPage - 1),
onPressed:
disabled ? null : () => _jumpToPage(pdf.currentPage - 1),
icon: const Icon(Icons.chevron_left),
tooltip: 'Prev',
),
Text(pageInfo, key: const Key('lbl_page_info')),
IconButton(
key: const Key('btn_next'),
onPressed: () => _jumpToPage(pdf.currentPage + 1),
onPressed:
disabled ? null : () => _jumpToPage(pdf.currentPage + 1),
icon: const Icon(Icons.chevron_right),
tooltip: 'Next',
),
@ -276,6 +323,7 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
child: TextField(
key: const Key('txt_goto'),
keyboardType: TextInputType.number,
enabled: !disabled,
onSubmitted: (v) {
final n = int.tryParse(v);
if (n != null) _jumpToPage(n);
@ -301,17 +349,20 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
),
)
.toList(),
onChanged: (v) {
if (v != null) {
ref.read(exportDpiProvider.notifier).state = v;
}
},
onChanged:
disabled
? null
: (v) {
if (v != null) {
ref.read(exportDpiProvider.notifier).state = v;
}
},
),
],
),
ElevatedButton(
key: const Key('btn_mark_signing'),
onPressed: _toggleMarkForSigning,
onPressed: disabled ? null : _toggleMarkForSigning,
child: Text(
pdf.markedForSigning ? 'Unmark Signing' : 'Mark for Signing',
),
@ -319,18 +370,18 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
if (pdf.loaded)
ElevatedButton(
key: const Key('btn_save_pdf'),
onPressed: _saveSignedPdf,
onPressed: disabled ? null : _saveSignedPdf,
child: const Text('Save Signed PDF'),
),
if (pdf.markedForSigning) ...[
OutlinedButton(
key: const Key('btn_load_signature_picker'),
onPressed: _loadSignatureFromFile,
onPressed: disabled ? null : _loadSignatureFromFile,
child: const Text('Load Signature from file'),
),
ElevatedButton(
key: const Key('btn_draw_signature'),
onPressed: _openDrawCanvas,
onPressed: disabled ? null : _openDrawCanvas,
child: const Text('Draw Signature'),
),
],
@ -473,10 +524,18 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
),
child: Stack(
children: [
if (sig.imageBytes != null)
Image.memory(sig.imageBytes!, fit: BoxFit.contain)
else
const Center(child: Text('Signature')),
Consumer(
builder: (context, ref, _) {
final processed = ref.watch(
processedSignatureImageProvider,
);
final bytes = processed ?? sig.imageBytes;
if (bytes == null) {
return const Center(child: Text('Signature'));
}
return Image.memory(bytes, fit: BoxFit.contain);
},
),
Positioned(
right: 0,
bottom: 0,

2
test/features/step/a_signature_image_is_selected.dart
View File

@ -15,4 +15,6 @@ Future<void> aSignatureImageIsSelected(WidgetTester tester) async {
container
.read(signatureProvider.notifier)
.setImageBytes(Uint8List.fromList([1, 2, 3]));
// Allow provider scheduler to process queued updates fully
await tester.pumpAndSettle();
}

32
test/features/step/nearwhite_background_becomes_transparent_in_the_preview.dart
View File

@ -1,5 +1,7 @@
import 'dart:typed_data';
import 'package:flutter_test/flutter_test.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:image/image.dart' as img;
import 'package:pdf_signature/ui/features/pdf/view_model/view_model.dart';
import '_world.dart';
@ -8,5 +10,35 @@ Future<void> nearwhiteBackgroundBecomesTransparentInThePreview(
WidgetTester tester,
) async {
final container = TestWorld.container ?? ProviderContainer();
TestWorld.container = container;
// Ensure the flag is on per the previous step
expect(container.read(signatureProvider).bgRemoval, isTrue);
// Build a tiny 2x1 image: left pixel near-white (should become transparent),
// right pixel black (should remain opaque).
final src = img.Image(width: 2, height: 1);
// Near-white >= thrHigh(245) to ensure fully transparent after processing
src.setPixelRgba(0, 0, 250, 250, 250, 255);
// Solid black stays opaque
src.setPixelRgba(1, 0, 0, 0, 0, 255);
final png = Uint8List.fromList(img.encodePng(src, level: 6));
// Feed this into signature state
container.read(signatureProvider.notifier).setImageBytes(png);
// Allow provider scheduler to process invalidations
await tester.pumpAndSettle();
// Get processed bytes
final processed = container.read(processedSignatureImageProvider);
expect(processed, isNotNull);
final decoded = img.decodeImage(processed!);
expect(decoded, isNotNull);
final outImg = decoded!.hasAlpha ? decoded : decoded.convert(numChannels: 4);
final p0 = outImg.getPixel(0, 0);
final p1 = outImg.getPixel(1, 0);
final a0 = (p0.aNormalized * 255).round();
final a1 = (p1.aNormalized * 255).round();
expect(a0, equals(0), reason: 'near-white should be transparent');
expect(a1, equals(255), reason: 'dark pixel should remain opaque');
}

2
test/features/step/the_user_changes_contrast_and_brightness_controls.dart
View File

@ -11,4 +11,6 @@ Future<void> theUserChangesContrastAndBrightnessControls(
container.read(signatureProvider.notifier)
..setContrast(1.3)
..setBrightness(0.2);
// Let provider updates settle
await tester.pumpAndSettle();
}

2
test/features/step/the_user_enables_background_removal.dart
View File

@ -7,4 +7,6 @@ import '_world.dart';
Future<void> theUserEnablesBackgroundRemoval(WidgetTester tester) async {
final container = TestWorld.container ?? ProviderContainer();
container.read(signatureProvider.notifier).setBgRemoval(true);
// Let provider updates settle
await tester.pumpAndSettle();
}