paint method

@override void paint(Canvas canvas, Size size)

Called whenever the object needs to paint. The given Canvas has its coordinate space configured such that the origin is at the top left of the box. The area of the box is the size of the size argument.

Paint operations should remain inside the given area. Graphical operations outside the bounds may be silently ignored, clipped, or not clipped. It may sometimes be difficult to guarantee that a certain operation is inside the bounds (e.g., drawing a rectangle whose size is determined by user inputs). In that case, consider calling Canvas.clipRect at the beginning of paint so everything that follows will be guaranteed to only draw within the clipped area.

Implementations should be wary of correctly pairing any calls to Canvas.save/Canvas.saveLayer and Canvas.restore, otherwise all subsequent painting on this canvas may be affected, with potentially hilarious but confusing results.

To paint text on a Canvas, use a TextPainter.

To paint an image on a Canvas:

1. Obtain an ImageStream, for example by calling ImageProvider.resolve on an AssetImage or NetworkImage object.

2. Whenever the ImageStream's underlying ImageInfo object changes (see ImageStream.addListener), create a new instance of your custom paint delegate, giving it the new ImageInfo object.

3. In your delegate's paint method, call the Canvas.drawImage, Canvas.drawImageRect, or Canvas.drawImageNine methods to paint the ImageInfo.image object, applying the ImageInfo.scale value to obtain the correct rendering size.

Implementation

@override
void paint(Canvas canvas, Size size) {
  final Size(:width, :height) = size;
  final shapeRadius = min(width, height) / 2;

  // Background Paint
  final bPaint = Paint()..color = const Color.fromARGB(255, 221, 212, 130);

  // Draw Thermometer Background
  canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromLTWH(bLeftPoint, bTopPoint, width, height * 0.9),
        const Radius.circular(
          radius,
        ),
      ),
      bPaint);

  // Center Scale
  final cPaint = Paint()
    ..color = Colors.black
    ..style = PaintingStyle.stroke
    ..strokeWidth = 3;
  final cLeftPoint = bLeftPoint + width * 0.38;
  final cTopPoint = bTopPoint + height * 0.05;
  final cWidth = width * 0.2;
  final cHeight = height * 0.7;

  // Draw Center Scale
  canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromLTWH(cLeftPoint, cTopPoint, cWidth, cHeight),
        const Radius.circular(radius),
      ),
      cPaint);

  // Bottom circle
  final bottomCircleRadius = shapeRadius * 0.5;
  final startOffset = Offset(cLeftPoint, cTopPoint);
  final endOffset = Offset(cLeftPoint + cWidth, cTopPoint);
  double y = ((startOffset.dy + endOffset.dy) / 2) + cHeight;
  double x = (startOffset.dx + endOffset.dx) / 2;
  final bottomCircleOffset = Offset(x, y);

  // Draw Bottom Circle
  canvas.drawCircle(bottomCircleOffset, bottomCircleRadius, cPaint);

  // Draw Inner Center Scale
  canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromLTWH(cLeftPoint, cTopPoint, cWidth, cHeight),
        const Radius.circular(radius),
      ),
      bPaint);

  // Draw Inner Bottom Circle
  canvas.drawCircle(bottomCircleOffset, bottomCircleRadius, bPaint);

  // Red Center Scale
  final rLeftPoint = cLeftPoint + cWidth * 0.32;
  final rTopPoint = cTopPoint + cHeight * topPosition;
  final rWidth = cWidth * 0.35;
  final rHeight = cHeight * (1 - topPosition);
  final rPaint = Paint()
    ..color = Colors.red
    ..style = PaintingStyle.fill;

  // Draw Red Center Scale
  canvas.drawRRect(
      RRect.fromRectAndRadius(
        Rect.fromLTWH(
          rLeftPoint,
          rTopPoint,
          rWidth,
          rHeight,
        ),
        const Radius.circular(radius),
      ),
      rPaint);

  // Draw Red Bottom Circle
  canvas.drawCircle(bottomCircleOffset, bottomCircleRadius * 0.75, rPaint);

  // Temperature Levels
  var levelStratPoint =
      Offset(cLeftPoint + cWidth, cTopPoint + cHeight * 0.04);
  final noLevelLength = cWidth * 0.9;
  final levelLength = cWidth * 0.6;
  final levelPaint = Paint()
    ..color = Colors.black
    ..style = PaintingStyle.stroke
    ..strokeWidth = 1;
  bool isLongLevel = true;
  int textValue = 50;
  bool isTextValueDec = true;

  // Draw Temp Levels
  for (var i = 0.0; i < noOfLevels; i++) {
    // Line Parameter
    levelStratPoint =
        Offset(cLeftPoint + cWidth, levelStratPoint.dy + cHeight * 0.04);
    double length = isLongLevel ? noLevelLength : levelLength;
    final levelEndPoint =
        Offset(levelStratPoint.dx + length, levelStratPoint.dy);

    // Line Draw
    canvas.drawLine(levelStratPoint, levelEndPoint, levelPaint);

    // Text Parameter
    final textOffset = Offset(
        levelEndPoint.dx + cWidth * 0.2, levelEndPoint.dy - cHeight * 0.014);
    if (isLongLevel) {
      // Text Draw
      TextPainter()
        ..textDirection = TextDirection.ltr
        ..text = TextSpan(
            text: textValue.toString(),
            style: TextStyle(
                color: Colors.black,
                fontWeight: FontWeight.bold,
                fontStyle: FontStyle.italic,
                fontSize: (cWidth + cHeight) / 40))
        ..layout()
        ..paint(canvas, textOffset);
      if (textValue == 0) {
        isTextValueDec = false;
      }
      textValue = isTextValueDec ? textValue - 10 : textValue + 10;
    }

    // Inversion at each step
    isLongLevel = !isLongLevel;
  }
}