protected override void OnRender(DrawingContext drawingContext)
{
//base.OnRender(drawingContext);
if (AxisPanel == null)
{
return;
}
//计算每个点之间的间距是多少
var cellWidth = GetCellInterval();
var xTransform = GetXTransform(cellWidth);
_startIndex = GetStartIndex(xTransform);
//没有点，或是只有一个都不能画线，在平面中过一点可以画无数条线
if (Datas == null || Datas.Count <= 1 || _startIndex >= Datas.Count)
{
return;
}
//实际圆的半径(线宽+半径)
//var realRadius = GetRealRadius();
var displayCount = (int)Math.Min(ActualWidth / cellWidth + 2, Datas.Count);
//每次动态产生对效能有影响，可以放到Arrange或是赋值之后计算一遍，此为偷懒写法
//或可以说时间换空间?
var pointList = new List <Point>(displayCount);
for (int i = 0, j = _startIndex; j < Datas.Count && i < displayCount; i++, j++)
{
var y = GetY(Datas[j]);
//if (realRadius == y)
// y = 0;
//注意横坐标有加realRadius
//var x = i * cellWidth + realRadius - Radius;
var x = i * cellWidth;
var point = new Point(x, y); // orginal : var point = new Point(i * cellWidth + realRadius, y);
pointList.Add(point);
}
drawingContext.PushTransform(new TranslateTransform(xTransform, 0));
//因为没有动画效果，并为了追求更好的效能，所以使用StreamGeometry
var geometry = new StreamGeometry();
using (var context = geometry.Open())
{
context.BeginFigure(pointList[0], true, false);
context.PolyLineTo(pointList, true, true);
context.Close();
}
geometry.Freeze();
//这些画笔也可以理解为时间换空间
var dashStyle = new DashStyle(LineDashArray, LineDashOffset);
dashStyle.Freeze();
#region shadow drawing
//Pen shadowPen = new Pen(ShadowColor, LineThickness);
//shadowPen.StartLineCap = PenLineCap.Round;
//shadowPen.EndLineCap = PenLineCap.Round;
//shadowPen.DashStyle = dashStyle;
//shadowPen.DashCap = LineDashCap;
//shadowPen.Freeze();
//if (IsShowShadow)
//{
// //draw offset line shadow
// drawingContext.PushTransform(new TranslateTransform(LineThickness * 0.312, -LineThickness * 0.681));
// drawingContext.DrawGeometry(null, shadowPen, geometry);
// drawingContext.Pop();
//}
#endregion
//draw line
var linePen = new Pen(LineColor, LineThickness)
{
DashCap = LineDashCap, DashStyle = dashStyle
};
linePen.Freeze();
drawingContext.DrawGeometry(null, linePen, geometry);
if (0 < Radius)
{
var ellipseLinePen = new Pen(LineColor, LineThickness / 2);
ellipseLinePen.Freeze();
//draw ellipse
foreach (var point in pointList)
{
drawingContext.DrawEllipse(PointColor, ellipseLinePen, point, Radius, Radius);
}
}
drawingContext.Pop();
}