paint method
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:
-
Obtain an ImageStream, for example by calling ImageProvider.resolve on an AssetImage or NetworkImage object.
-
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.
-
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) {
// Professional padding (constants for performance)
const leftPadding = 50.0;
const rightPadding = 20.0;
const topPadding = 20.0;
const bottomPadding = 40.0;
final chartSize = Size(
size.width - leftPadding - rightPadding,
size.height - topPadding - bottomPadding,
);
final chartOffset = const Offset(leftPadding, topPadding);
// Calculate bounds (optimized single pass)
if (dataSets.isEmpty) return;
double minX = double.infinity;
double maxX = double.negativeInfinity;
double maxY = double.negativeInfinity;
// Single pass through all points for better performance
for (final dataSet in dataSets) {
for (final point in dataSet.dataPoints) {
if (point.x < minX) minX = point.x;
if (point.x > maxX) maxX = point.x;
if (point.y > maxY) maxY = point.y;
}
}
if (minX == double.infinity ||
!minX.isFinite ||
!maxX.isFinite ||
!maxY.isFinite) {
return; // No valid data
}
final minY = 0.0; // Always start from 0 for better visualization
// Ensure maxY is positive and valid
final maxYAdjusted = maxY > 0 ? maxY * 1.15 : 1.0;
// Add small padding for X axis
final xRange = maxX - minX;
final xPadding = (xRange > 0 && xRange.isFinite) ? xRange * 0.05 : 0.0;
// Validate chart size
if (!chartSize.width.isFinite ||
!chartSize.height.isFinite ||
chartSize.width <= 0 ||
chartSize.height <= 0) {
return;
}
// Save canvas state
canvas.save();
canvas.translate(chartOffset.dx, chartOffset.dy);
// Draw grid
drawGrid(canvas, chartSize, minX, maxX, minY, maxYAdjusted);
// Draw axes
drawAxes(canvas, chartSize, minX, maxX, minY, maxYAdjusted);
// Draw each dataset
for (final dataSet in dataSets) {
if (dataSet.dataPoints.isEmpty) continue;
// Convert points to canvas coordinates with padding
final points = dataSet.dataPoints
.map((point) {
return pointToCanvas(
point,
chartSize,
minX - xPadding,
maxX + xPadding,
minY,
maxYAdjusted,
);
})
.where((offset) => offset.dx.isFinite && offset.dy.isFinite)
.toList();
// Skip if no valid points
if (points.isEmpty) continue;
// Draw area fill with professional gradient and animation
if (showArea) {
final areaPath = Path();
areaPath.moveTo(points.first.dx, chartSize.height);
// Use same animated points as line
final totalPoints = points.length;
final animatedPoints = (totalPoints * animationProgress).ceil();
// Create smooth bezier curve
for (int i = 0; i < animatedPoints && i < points.length; i++) {
final currentPoint = points[i];
// Validate point before using
if (!currentPoint.dx.isFinite || !currentPoint.dy.isFinite) continue;
if (i == 0) {
areaPath.lineTo(currentPoint.dx, currentPoint.dy);
} else {
final prevPoint = points[i - 1];
// Validate previous point
if (!prevPoint.dx.isFinite || !prevPoint.dy.isFinite) continue;
// Interpolate the last point if animation is in progress
Offset targetPoint = currentPoint;
if (i == animatedPoints - 1 && animationProgress < 1.0) {
final partialProgress =
(animationProgress * totalPoints) - (i - 1);
final lerpedPoint =
Offset.lerp(prevPoint, currentPoint, partialProgress);
if (lerpedPoint != null &&
lerpedPoint.dx.isFinite &&
lerpedPoint.dy.isFinite) {
targetPoint = lerpedPoint;
}
}
final dx = targetPoint.dx - prevPoint.dx;
if (!dx.isFinite) continue;
final controlPoint1 = Offset(
prevPoint.dx + dx * curveSmoothness,
prevPoint.dy,
);
final controlPoint2 = Offset(
targetPoint.dx - dx * curveSmoothness,
targetPoint.dy,
);
// Validate control points before using
if (!controlPoint1.dx.isFinite ||
!controlPoint1.dy.isFinite ||
!controlPoint2.dx.isFinite ||
!controlPoint2.dy.isFinite ||
!targetPoint.dx.isFinite ||
!targetPoint.dy.isFinite) {
continue;
}
areaPath.cubicTo(
controlPoint1.dx,
controlPoint1.dy,
controlPoint2.dx,
controlPoint2.dy,
targetPoint.dx,
targetPoint.dy,
);
}
}
// Complete the area path
if (animatedPoints > 0 && points.isNotEmpty) {
Offset lastPoint;
if (animatedPoints == points.length) {
lastPoint = points.last;
} else {
final lerpedPoint = Offset.lerp(
points[animatedPoints - 1],
points[math.min(animatedPoints, points.length - 1)],
animationProgress,
);
lastPoint = (lerpedPoint != null &&
lerpedPoint.dx.isFinite &&
lerpedPoint.dy.isFinite)
? lerpedPoint
: points.last;
}
if (lastPoint.dx.isFinite && lastPoint.dy.isFinite) {
areaPath.lineTo(lastPoint.dx, chartSize.height);
}
}
areaPath.close();
// Professional multi-stop gradient with animation opacity
final areaPaint = Paint()
..shader = LinearGradient(
begin: Alignment.topCenter,
end: Alignment.bottomCenter,
colors: [
dataSet.color.withValues(alpha: 0.4 * animationProgress),
dataSet.color.withValues(alpha: 0.15 * animationProgress),
dataSet.color.withValues(alpha: 0.0),
],
stops: const [0.0, 0.5, 1.0],
).createShader(Rect.fromLTWH(0, 0, chartSize.width, chartSize.height))
..style = PaintingStyle.fill;
canvas.drawPath(areaPath, areaPaint);
}
// Draw line with smooth bezier curves and animation
final linePath = Path();
if (points.isNotEmpty &&
points.first.dx.isFinite &&
points.first.dy.isFinite) {
linePath.moveTo(points.first.dx, points.first.dy);
}
// Calculate how many points to draw based on animation progress
final totalPoints = points.length;
final animatedPoints = (totalPoints * animationProgress).ceil();
for (int i = 1; i < animatedPoints && i < points.length; i++) {
final prevPoint = points[i - 1];
final currentPoint = points[i];
// Validate points before using
if (!prevPoint.dx.isFinite ||
!prevPoint.dy.isFinite ||
!currentPoint.dx.isFinite ||
!currentPoint.dy.isFinite) {
continue;
}
final dx = currentPoint.dx - prevPoint.dx;
if (!dx.isFinite) continue;
// Interpolate the last point if animation is in progress
Offset targetPoint = currentPoint;
if (i == animatedPoints - 1 && animationProgress < 1.0) {
final partialProgress = (animationProgress * totalPoints) - (i - 1);
final lerpedPoint =
Offset.lerp(prevPoint, currentPoint, partialProgress);
if (lerpedPoint != null &&
lerpedPoint.dx.isFinite &&
lerpedPoint.dy.isFinite) {
targetPoint = lerpedPoint;
}
}
// Better bezier control points for smoother curves
final controlPoint1 = Offset(
prevPoint.dx + dx * curveSmoothness,
prevPoint.dy,
);
final controlPoint2 = Offset(
targetPoint.dx - dx * curveSmoothness,
targetPoint.dy,
);
// Validate control points before using
if (!controlPoint1.dx.isFinite ||
!controlPoint1.dy.isFinite ||
!controlPoint2.dx.isFinite ||
!controlPoint2.dy.isFinite ||
!targetPoint.dx.isFinite ||
!targetPoint.dy.isFinite) {
continue;
}
linePath.cubicTo(
controlPoint1.dx,
controlPoint1.dy,
controlPoint2.dx,
controlPoint2.dy,
targetPoint.dx,
targetPoint.dy,
);
}
// Professional line styling with subtle glow
final linePaint = Paint()
..color = dataSet.color
..strokeWidth = lineWidth
..style = PaintingStyle.stroke
..strokeCap = StrokeCap.round
..strokeJoin = StrokeJoin.round
..maskFilter = const MaskFilter.blur(BlurStyle.normal, 1.0);
canvas.drawPath(linePath, linePaint);
// Draw a brighter overlay for depth
final overlayPaint = Paint()
..color = dataSet.color.withValues(alpha: 0.6)
..strokeWidth = lineWidth * 0.5
..style = PaintingStyle.stroke
..strokeCap = StrokeCap.round
..strokeJoin = StrokeJoin.round;
canvas.drawPath(linePath, overlayPaint);
// Draw points with professional styling and animation
if (showPoints) {
final totalPoints = points.length;
final animatedPoints = (totalPoints * animationProgress).ceil();
for (int i = 0; i < animatedPoints && i < points.length; i++) {
final point = points[i];
// Validate point before using
if (!point.dx.isFinite || !point.dy.isFinite) continue;
final pointOpacity = i < animatedPoints - 1 ? 1.0 : animationProgress;
// Check if this point is selected or hovered
final isSelected = selectedPoint != null &&
selectedPoint!.isHit &&
selectedPoint!.datasetIndex == dataSets.indexOf(dataSet) &&
selectedPoint!.elementIndex == i;
final isHovered = hoveredPoint != null &&
hoveredPoint!.isHit &&
hoveredPoint!.datasetIndex == dataSets.indexOf(dataSet) &&
hoveredPoint!.elementIndex == i;
// Outer glow with animation (larger if selected or hovered)
final glowRadius = isSelected ? 10.0 : (isHovered ? 8.0 : 6.0);
final glowOpacity = isSelected ? 0.4 : (isHovered ? 0.3 : 0.2);
final glowPaint = Paint()
..color =
dataSet.color.withValues(alpha: glowOpacity * pointOpacity)
..style = PaintingStyle.fill;
canvas.drawCircle(point, glowRadius, glowPaint);
// Main point with animation (larger if selected or hovered)
final pointRadius = isSelected ? 6.5 : (isHovered ? 5.5 : 4.5);
final pointPaint = Paint()
..color = dataSet.color.withValues(alpha: pointOpacity)
..style = PaintingStyle.fill;
canvas.drawCircle(point, pointRadius, pointPaint);
// Inner highlight with animation
final highlightPaint = Paint()
..color = Colors.white.withValues(alpha: 0.8 * pointOpacity)
..style = PaintingStyle.fill;
canvas.drawCircle(point, 2, highlightPaint);
// Border with animation (thicker and white if selected)
final borderWidth = isSelected ? 3.0 : (isHovered ? 2.0 : 1.5);
final borderPaint = Paint()
..color = isSelected ? Colors.white : theme.backgroundColor
..style = PaintingStyle.stroke
..strokeWidth = borderWidth;
canvas.drawCircle(point, pointRadius, borderPaint);
}
}
}
canvas.restore();
// Draw axis labels with proper bounds
canvas.save();
canvas.translate(chartOffset.dx, chartOffset.dy);
drawAxisLabels(
canvas,
chartSize,
minX - xPadding,
maxX + xPadding,
minY,
maxYAdjusted,
);
canvas.restore();
}