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) {
double strokeWidth = 2;
Paint totalCircle = Paint();
double radius;
Paint dataPlotter = Paint();
Paint lineHighlighter = Paint();
Offset pointerOffset;
Path path = Path();
Path path2 = Path();
double singleUnitOfWidth;
double singleUnitOfHeight;
int totalNumberOfDataPoints;
double centerPositionCalculation;
double horizontalPositionOfTheFirstDataPoint;
double verticalPositionOfTheFirstDataPoint;
double verticalPostionForAllDataPoints;
for (int i = 0; i < dataPoints.length; i++) {
// This calculates the total number of data points in a single line.
// It is used to calculate the single unit of width
totalNumberOfDataPoints = dataPoints[i].values.length;
// singleUnitOfWidth is the total width of the canvas divided by the number of data points on a line.
// This helps in finding the exact position of a data point.
singleUnitOfWidth = size.width / totalNumberOfDataPoints;
// singleUnitOfHeight is the total height of the canvas divided by the maximum data point from all the lines.
// This helps in finding the exact position of a data point.
singleUnitOfHeight = size.height / max;
// Center position is calculated the same way as single unit of width except the total number of data points is multiplied by 2.
// This centers the data point of every xaxis increment.
centerPositionCalculation = (size.width / (totalNumberOfDataPoints * 2));
horizontalPositionOfTheFirstDataPoint =
((singleUnitOfWidth * totalNumberOfDataPoints) -
centerPositionCalculation);
verticalPositionOfTheFirstDataPoint = (singleUnitOfHeight) *
(dataPoints[i].values[0] < 0 ? 0 : dataPoints[i].values[0]);
if (dataPoints[i].filledGraph) {
totalCircle
..strokeWidth = strokeWidth
..color = dataPoints[i].dataPointColor
..style = PaintingStyle.stroke;
radius = dataPoints[i].dataPointSize;
dataPlotter
..color = dataPoints[i].fillColor
..style = PaintingStyle.fill;
lineHighlighter
..color = dataPoints[i].lineColor
..strokeWidth = dataPoints[i].lineWidth
..style = PaintingStyle.stroke;
// Offset of the first data point
// To get the offset of the first we need to calculate the the horizontal position and the vertical position of the data point
// To calculate the horizontal position we multiply single unit of width with the total number of points and subtract it with the width of the canvas.
// We also subtract the center position calculation from the above equation.
// To calculate the vertical position we simply multiply the single unit of height with the number of data points and subtract it from the total height of the canvas.
// Incase the calculated vertical position is less than zero we equate it to 0 to prevent over flow.
pointerOffset = Offset(
size.width - horizontalPositionOfTheFirstDataPoint,
((size.height - verticalPositionOfTheFirstDataPoint) +
strokeWidth) -
(topSpacing / 2));
// Moving our painter to the first point
path.moveTo(pointerOffset.dx, pointerOffset.dy);
path2.moveTo(pointerOffset.dx, pointerOffset.dy);
if (dataPoints[i].showDataPoints) {
canvas.drawCircle(pointerOffset, radius, totalCircle);
}
for (int j = 1; j < dataPoints[i].values.length; j++) {
verticalPostionForAllDataPoints = ((singleUnitOfHeight) *
(dataPoints[i].values[j] < 0 ? 0 : dataPoints[i].values[j]));
// Calculating the offset of the data points
// To get the offset of the data points we need to calculate the the horizontal position and the vertical position of the data points
// To calculate the horizontal position we multiply single unit of width with the number of positions the point holds on the xaxis from the right side and subtract it with the width of the canvas.
// We also subtract the center position calculation from the above equation.
// To calculate the vertical position we simply multiply the single unit of height with the number of data points and subtract it from the total height of the canvas.
// Incase the calculated vertical position is less than zero we equate it to 0 to prevent over flow.
pointerOffset = Offset(
size.width -
((singleUnitOfWidth * (totalNumberOfDataPoints - j)) -
centerPositionCalculation),
((size.height - verticalPostionForAllDataPoints) + strokeWidth) -
(topSpacing / 2));
path.lineTo(pointerOffset.dx, pointerOffset.dy);
path2.lineTo(pointerOffset.dx, pointerOffset.dy);
if (dataPoints[i].showDataPoints) {
canvas.drawCircle(pointerOffset, radius, totalCircle);
}
}
path.lineTo(
((singleUnitOfWidth * totalNumberOfDataPoints) -
centerPositionCalculation),
size.height - (topSpacing / 2));
path.close();
canvas.drawPath(path, dataPlotter);
canvas.drawPath(path2, lineHighlighter);
} else {
totalCircle
..strokeWidth = strokeWidth
..color = dataPoints[i].dataPointColor
..style = PaintingStyle.stroke;
radius = dataPoints[i].dataPointSize;
dataPlotter
..color = dataPoints[i].lineColor
..strokeWidth = dataPoints[i].lineWidth
..style = PaintingStyle.stroke;
// Offset of the first data point
// To get the offset of the first we need to calculate the the horizontal position and the vertical position of the data point
// To calculate the horizontal position we multiply single unit of width with the total number of points and subtract it with the width of the canvas.
// We also subtract the center position calculation from the above equation.
// To calculate the vertical position we simply multiply the single unit of height with the number of data points and subtract it from the total height of the canvas.
// Incase the calculated vertical position is less than zero we equate it to 0 to prevent over flow.
pointerOffset = Offset(
size.width - horizontalPositionOfTheFirstDataPoint,
((size.height - (verticalPositionOfTheFirstDataPoint)) +
strokeWidth) -
(topSpacing / 2));
path.moveTo(pointerOffset.dx, pointerOffset.dy);
if (dataPoints[i].showDataPoints) {
canvas.drawCircle(pointerOffset, radius, totalCircle);
}
for (int j = 1; j < totalNumberOfDataPoints; j++) {
verticalPostionForAllDataPoints = ((singleUnitOfHeight) *
(dataPoints[i].values[j] < 0 ? 0 : dataPoints[i].values[j]));
// Calculating the offset of the data points.
// To get the offset of the data points we need to calculate the the horizontal position and the vertical position of the data points
// To calculate the horizontal position we multiply single unit of width with the number of positions the point holds on the xaxis from the right side and subtract it with the width of the canvas.
// We also subtract the center position calculation from the above equation.
// To calculate the vertical position we simply multiply the single unit of height with the number of data points and subtract it from the total height of the canvas.
// Incase the calculated vertical position is less than zero we equate it to 0 to prevent over flow.
pointerOffset = Offset(
size.width -
((singleUnitOfWidth * (totalNumberOfDataPoints - j)) -
centerPositionCalculation),
((size.height - verticalPostionForAllDataPoints) + strokeWidth) -
(topSpacing / 2));
path.lineTo(pointerOffset.dx, pointerOffset.dy);
if (dataPoints[i].showDataPoints) {
canvas.drawCircle(pointerOffset, radius, totalCircle);
}
}
canvas.drawPath(path, dataPlotter);
}
}
}