paint method

@override void paint(Canvas canvas, Size size, WorldToScreen worldToScreen, ScreenToWorld screenToWorld, double scale,)

Called by the canvas to paint this item onto the screen.

The canvas and size are provided by the Flutter framework. Use worldToScreen to translate mathematical coordinates into on-screen pixels.

Implementation

@override
void paint(
  Canvas canvas,
  Size size,
  WorldToScreen worldToScreen,
  ScreenToWorld screenToWorld,
  double scale,
) {
  if (equation.trim().isEmpty) return;

  final shadowPaint = Paint()
    ..color = color.withOpacity(0.25)
    ..strokeWidth = lineWidth
    ..style = PaintingStyle.stroke
    ..strokeCap = StrokeCap.round
    ..strokeJoin = StrokeJoin.round
    ..maskFilter = const MaskFilter.blur(BlurStyle.normal, 3.0);

  final basePaint = Paint()
    ..color = color
    ..strokeWidth = lineWidth
    ..style = PaintingStyle.stroke
    ..strokeCap = StrokeCap.round
    ..strokeJoin = StrokeJoin.round;

  try {
    final expressionParser = GrammarParser();
    final mathExpression = expressionParser.parse(equation);
    final contextModel = ContextModel();
    final functionPath = Path();
    bool isFirstPoint = true;

    for (double pixelX = 0; pixelX <= size.width; pixelX += 2) {
      final worldCoordinates = screenToWorld(pixelX, 0);
      contextModel.bindVariable(Variable('x'), Number(worldCoordinates.dx));
      final logicalY = mathExpression.evaluate(
          EvaluationType.REAL, contextModel) as double;
      final screenCoordinates = worldToScreen(worldCoordinates.dx, logicalY);

      if (screenCoordinates.dy.isInfinite ||
          screenCoordinates.dy.isNaN ||
          screenCoordinates.dy < -size.height * 2 ||
          screenCoordinates.dy > size.height * 3) {
        isFirstPoint = true;
        continue;
      }

      if (isFirstPoint) {
        functionPath.moveTo(pixelX, screenCoordinates.dy);
        isFirstPoint = false;
      } else {
        functionPath.lineTo(pixelX, screenCoordinates.dy);
      }
    }

    canvas.drawPath(functionPath.shift(const Offset(0, 2)), shadowPaint);
    canvas.drawPath(functionPath, basePaint);
  } catch (_) {}
}