drawAxisLabels method

void drawAxisLabels(Canvas canvas, Size size, double minX, double maxX, double minY, double maxY, { List<ChartDataSet>? dataSets, })

Draw axis labels (optimized with text style caching).

Renders numeric labels along the X and Y axes to help users read values. Uses efficient text rendering with cached styles and smart formatting.

Parameters:

• canvas - The canvas to draw on
• size - The size of the chart area
• minX, maxX, minY, maxY - The data bounds for label values

Labels are automatically formatted (integers when possible, decimals otherwise). The number of labels is automatically adjusted based on the chart size.

The labels will only be drawn if showLabel and showAxis are true.

If dataSets are provided, labels from ChartDataPoint.label will be used for X-axis labels when available, falling back to numeric values.

Example

drawAxisLabels(canvas, chartSize, 0, 100, 0, 50);
// Or with data points for custom labels:
drawAxisLabels(canvas, chartSize, 0, 100, 0, 50, dataSets: dataSets);

Implementation

void drawAxisLabels(
  Canvas canvas,
  Size size,
  double minX,
  double maxX,
  double minY,
  double maxY, {
  List<ChartDataSet>? dataSets,
}) {
  if (!showLabel || !showAxis || !theme.showAxis) return;

  // Validate size and ranges
  if (size.width <= 0 || size.height <= 0) return;
  if (!size.width.isFinite || !size.height.isFinite) return;

  final xRange = maxX - minX;
  final yRange = maxY - minY;

  // Validate ranges are valid and non-zero
  if (!xRange.isFinite || !yRange.isFinite) return;

  // Use theme text style if available
  final textStyle = theme.axisLabelStyle ?? TextStyle(
    color: theme.axisColor.withValues(alpha: 0.8),
    fontSize: 11,
    fontWeight: FontWeight.w500,
    letterSpacing: 0.2,
  );

  // X-axis labels - use labels from data points if available
  final xLabelsCount =
      math.max(1, math.min(6, (xRange > 0 ? xRange : 1).ceil().toInt()));
  if (xLabelsCount > 0 && xRange > 0) {
    // Try to use labels from data points
    if (dataSets != null &&
        dataSets.isNotEmpty &&
        dataSets.any((ds) => ds.dataPoint.label != null)) {
      // Use labels from data points - show labels at actual data point positions
      // Use a map to deduplicate labels by x position (only show one label per x value)
      final Map<double, String> xLabels = {};
      for (final dataSet in dataSets) {
        final point = dataSet.dataPoint;

        // Skip if no label or invalid x value
        if (point.label == null || !point.x.isFinite) continue;

        // Store label for this x position (first label wins if duplicates exist)
        if (!xLabels.containsKey(point.x)) {
          xLabels[point.x] = point.label!;
        }
      }

      // Draw labels for unique x positions
      for (final entry in xLabels.entries) {
        final xValue = entry.key;
        final label = entry.value;

        // Calculate x position based on point.x
        final normalizedX = xRange > 0 ? (xValue - minX) / xRange : 0.5;
        final x = normalizedX * size.width;

        // Only draw if within chart bounds
        if (!x.isFinite || x < 0 || x > size.width) continue;

        final textPainter = TextPainter(
          text: TextSpan(text: label, style: textStyle),
          textDirection: TextDirection.ltr,
        );
        textPainter.layout();

        _paintRotatedLabel(
          canvas,
          textPainter,
          Offset(x, size.height + 12), // Increased padding
          theme.xAxisLabelRotation,
        );
      }
    } else {
      // Fall back to numeric labels
      final xStep = size.width / xLabelsCount;

      for (int i = 0; i <= xLabelsCount; i++) {
        final x = xStep * i;
        if (!x.isFinite) continue;

        final value = minX + xRange * (i / xLabelsCount);
        if (!value.isFinite) continue;

        final displayValue = value % 1 == 0
            ? value.toInt().toString()
            : value.toStringAsFixed(1);

        final textPainter = TextPainter(
          text: TextSpan(text: displayValue, style: textStyle),
          textDirection: TextDirection.ltr,
        );
        textPainter.layout();

        // For numeric labels, use theme rotation (no per-point rotation available)
        _paintRotatedLabel(
          canvas,
          textPainter,
          Offset(x, size.height + 12), // Increased padding
          theme.xAxisLabelRotation,
        );
      }
    }
  }

  // Y-axis labels - better formatting with pre-calculated values
  const yLabels = 5;
  if (yLabels > 0 && yRange > 0) {
    final yStep = size.height / yLabels;

    for (int i = 0; i <= yLabels; i++) {
      final y = size.height - yStep * i;
      if (!y.isFinite) continue;

      final value = minY + yRange * (i / yLabels);
      if (!value.isFinite) continue;

      final displayValue = value % 1 == 0
          ? value.toInt().toString()
          : value.toStringAsFixed(1);

      final textPainter = TextPainter(
        text: TextSpan(text: displayValue, style: textStyle),
        textDirection: TextDirection.ltr,
      );
      textPainter.layout();

      // Position label to the left of the Y-axis, centered vertically
      // Ensure we don't go too far left (assuming standard padding)
      final labelX = -textPainter.width - 12; // Increased padding

      _paintRotatedLabel(
        canvas,
        textPainter,
        Offset(labelX, y),
        theme.yAxisLabelRotation,
      );
    }
  }
}