Add FullPage widget

@@ -17,6 +17,7 @@
 - Implement Image orientation
 - Add Exif reader
 - Add support for GreyScale Jpeg
+- Add FullPage widget
 
 ## 1.3.23
 

@@ -666,3 +666,74 @@ class Builder extends StatelessWidget {
   @override
   Widget build(Context context) => builder(context);
 }
+
+class FullPage extends SingleChildWidget {
+  FullPage({
+    @required this.ignoreMargins,
+    Widget child,
+  })  : assert(ignoreMargins != null),
+        super(child: child);
+
+  final bool ignoreMargins;
+
+  BoxConstraints _getConstraints(Context context) {
+    return ignoreMargins
+        ? BoxConstraints.tightFor(
+            width: context.page.pageFormat.width,
+            height: context.page.pageFormat.height,
+          )
+        : BoxConstraints.tightFor(
+            width: context.page.pageFormat.availableWidth,
+            height: context.page.pageFormat.availableHeight,
+          );
+  }
+
+  PdfRect _getBox(Context context) {
+    final PdfRect box = _getConstraints(context).constrainRect();
+    if (ignoreMargins) {
+      return box;
+    }
+
+    return PdfRect.fromPoints(
+        PdfPoint(
+          context.page.pageFormat.marginLeft,
+          context.page.pageFormat.marginTop,
+        ),
+        box.size);
+  }
+
+  @override
+  void layout(Context context, BoxConstraints constraints,
+      {bool parentUsesSize = false}) {
+    final BoxConstraints constraints = _getConstraints(context);
+
+    if (child != null) {
+      child.layout(context, constraints, parentUsesSize: false);
+      assert(child.box != null);
+    }
+
+    box = _getBox(context);
+    print('layout box: $box');
+  }
+
+  @override
+  void debugPaint(Context context) {}
+
+  @override
+  void paint(Context context) {
+    super.paint(context);
+
+    if (child == null) {
+      return;
+    }
+
+    final PdfRect box = _getBox(context);
+    final Matrix4 mat = Matrix4.tryInvert(context.canvas.getTransform());
+    mat.translate(box.x, box.y);
+    context.canvas
+      ..saveContext()
+      ..setTransform(mat);
+    child.paint(context);
+    context.canvas.restoreContext();
+  }
+}

@@ -104,6 +104,14 @@ class Page {
       page: _pdfPage,
       canvas: canvas,
     ).inheritFrom(calculatedTheme);
+
+    assert(() {
+      if (Document.debug) {
+        debugPaint(context);
+      }
+      return true;
+    }());
+
     if (pageTheme.buildBackground != null) {
       final Widget child = pageTheme.buildBackground(context);
       if (child != null) {
@@ -111,6 +119,7 @@ class Page {
         paint(child, context);
       }
     }
+
     if (_build != null) {
       final Widget child = _build(context);
       if (child != null) {
@@ -118,6 +127,7 @@ class Page {
         paint(child, context);
       }
     }
+
     if (pageTheme.buildForeground != null) {
       final Widget child = pageTheme.buildForeground(context);
       if (child != null) {
@@ -144,13 +154,6 @@ class Page {
 
   @protected
   void paint(Widget child, Context context) {
-    assert(() {
-      if (Document.debug) {
-        debugPaint(context);
-      }
-      return true;
-    }());
-
     if (child == null) {
       return;
     }

@@ -25,7 +25,10 @@ void main() {
     final Document pdf = Document();
 
     final PageTheme pageTheme = PageTheme(
-      buildBackground: (Context context) => Watermark.text('DRAFT'),
+      buildBackground: (Context context) => FullPage(
+        ignoreMargins: true,
+        child: Watermark.text('DRAFT'),
+      ),
       buildForeground: (Context context) => Align(
         alignment: Alignment.bottomLeft,
         child: SizedBox(