createMissingBitmap method
creates a tile bitmap with the information that the rendering of the given tile is not yet finished. This tile will normally be replaced when the rendering finishes.
Implementation
Future<TileBitmap> createMissingBitmap(int tileSize) async {
var pictureRecorder = ui.PictureRecorder();
var canvas = ui.Canvas(pictureRecorder);
var paint = ui.Paint();
paint.strokeWidth = 1;
paint.color = const ui.Color(0xffaaaaaa);
paint.isAntiAlias = true;
canvas.drawLine(ui.Offset(_margin, _margin),
ui.Offset(tileSize - _margin, _margin), paint);
canvas.drawLine(ui.Offset(_margin, _margin),
ui.Offset(_margin, tileSize - _margin), paint);
canvas.drawLine(ui.Offset(tileSize - _margin, _margin),
ui.Offset(tileSize - _margin, tileSize - _margin), paint);
canvas.drawLine(ui.Offset(_margin, tileSize - _margin),
ui.Offset(tileSize - _margin, tileSize - _margin), paint);
ui.ParagraphBuilder builder = ui.ParagraphBuilder(
ui.ParagraphStyle(fontSize: 10.0, textAlign: TextAlign.center),
)
..pushStyle(ui.TextStyle(color: paint.color))
..addText("Waiting for rendering...");
canvas.drawParagraph(
builder.build()
..layout(ui.ParagraphConstraints(width: tileSize.toDouble())),
Offset(0, tileSize / 2));
var pic = pictureRecorder.endRecording();
ui.Image img = await pic.toImage(tileSize.toInt(), tileSize.toInt());
// var byteData = await img.toByteData(format: ui.ImageByteFormat.png);
// var buffer = byteData.buffer.asUint8List();
return FlutterTileBitmap(img);
}