Virtualization

[dgkorenje]

Can you make virtualisation possible in order to accelerate speed for large amount of points.

Currently I am adding/removing points from series as I scroll to position. With option I have set how many points I can show on the chart.
I have 3 collections of points in the background - raw points, processed points and displayed points. Displayed points are linked to series values. All points are in observable collection and are updated.
Bottlenecks are determining how many points are displayed. I'll have to sort this out and make a proper algorithm since I don't have to scan whole collection to get visible count.

Also note that chart series dissapears on helper chart for no reason after setting updates series (new collection set to series). I tried update, refresh etc... nothing works. Only if I move something on the chart on X direction.

https://youtu.be/CKK2RSVnKtE

For other I can share downsample methods.

Private Function DownsampleWithMinMax(Of T)(points As List(Of T), maxPoints As Integer) As List(Of T)
        If points Is Nothing OrElse points.Count = 0 Then Return New List(Of T)
        If maxPoints <= 0 OrElse points.Count <= maxPoints Then Return New List(Of T)(points)

        ' Each bucket adds 4 points: open, high, low, close
        Dim bucketCount As Integer = Math.Max(1, maxPoints \ 4)
        Dim bucketSize As Integer = Math.Max(1, points.Count \ bucketCount)

        Dim result As New List(Of T)(bucketCount * 4)

        Dim getYMin As Func(Of T, Double)
        Dim getYMax As Func(Of T, Double)
        Dim getX As Func(Of T, Long)

        If GetType(T) Is GetType(FinancialPoint) Then
            getYMin = Function(p) DirectCast(CObj(p), FinancialPoint).Low
            getYMax = Function(p) DirectCast(CObj(p), FinancialPoint).High
            getX = Function(p) DirectCast(CObj(p), FinancialPoint).Date.Ticks
        ElseIf GetType(T) Is GetType(DateTimePoint) Then
            getYMin = Function(p) DirectCast(CObj(p), DateTimePoint).Value
            getYMax = getYMin
            getX = Function(p) DirectCast(CObj(p), DateTimePoint).DateTime.Ticks
        ElseIf GetType(T) Is GetType(ObservablePoint) Then
            getYMin = Function(p) DirectCast(CObj(p), ObservablePoint).Y
            getYMax = getYMin
            getX = Function(p) CLng(DirectCast(CObj(p), ObservablePoint).X)
        ElseIf GetType(T) Is GetType(LogPoint) Then
            getYMin = Function(p) DirectCast(CObj(p), LogPoint).Y
            getYMax = getYMin
            getX = Function(p) CLng(DirectCast(CObj(p), LogPoint).X)
        ElseIf GetType(T) Is GetType(ObservableValue) Then
            getYMin = Function(p) DirectCast(CObj(p), ObservableValue).Value
            getYMax = getYMin
            getX = Function(p) CLng(DirectCast(CObj(p), ObservableValue).Coordinate.SecondaryValue)
        ElseIf GetType(T) Is GetType(FinancialPointI) Then
            getYMin = Function(p) DirectCast(CObj(p), FinancialPointI).Low
            getYMax = Function(p) DirectCast(CObj(p), FinancialPointI).High
            getX = Function(p) CLng(DirectCast(CObj(p), FinancialPointI).Coordinate.SecondaryValue)
        Else
            Throw New InvalidOperationException("Unsupported point type: " & GetType(T).Name)
        End If

        Dim i As Integer = 0
        While i < points.Count
            Dim openPoint As T = points(i)
            Dim closePoint As T = points(Math.Min(i + bucketSize - 1, points.Count - 1))
            Dim minPoint As T = openPoint
            Dim maxPoint As T = openPoint
            Dim minVal As Double = getYMin(openPoint)
            Dim maxVal As Double = getYMax(openPoint)

            Dim jEnd As Integer = Math.Min(i + bucketSize, points.Count)
            For j As Integer = i + 1 To jEnd - 1
                Dim p As T = points(j)
                Dim yLow As Double = getYMin(p)
                Dim yHigh As Double = getYMax(p)
                If yLow < minVal Then
                    minVal = yLow
                    minPoint = p
                End If
                If yHigh > maxVal Then
                    maxVal = yHigh
                    maxPoint = p
                End If
            Next

            ' Add points in chronological order
            Dim ordered = New List(Of T) From {openPoint, minPoint, maxPoint, closePoint}
            ordered.Sort(Function(a, b) getX(a).CompareTo(getX(b)))
            result.AddRange(ordered)

            i += bucketSize
        End While

        Return result
    End Function

    Function DownsampleByFactorMinMax(Of T)(points As IEnumerable(Of T), factor As Integer) As ObservableCollection(Of T)
        If points Is Nothing OrElse points.Count = 0 OrElse factor <= 1 Then Return points

        Dim batchSize As Integer = factor * 2
        Dim count As Integer = points.Count
        Dim result As New ObservableCollection(Of T)

        ' Fast delegates for Y, X, and clone/update (to keep original type)
        Dim getY As Func(Of T, Double)
        Dim getX As Func(Of T, Long)
        Dim clonePoint As Func(Of T, T, T, T) = Nothing ' Only for Financial points

        If GetType(T) Is GetType(FinancialPoint) Then
            getY = Function(p) DirectCast(CObj(p), FinancialPoint).High ' We'll track High and Low separately
            getX = Function(p) DirectCast(CObj(p), FinancialPoint).Date.Ticks
            clonePoint = Function(firstP, minP, maxP)
                             Dim fpFirst = DirectCast(CObj(firstP), FinancialPoint)
                             Dim fpMin = DirectCast(CObj(minP), FinancialPoint)
                             Dim fpMax = DirectCast(CObj(maxP), FinancialPoint)
                             Dim fpLast = DirectCast(CObj(maxP), FinancialPoint)
                             Return DirectCast(CObj(New FinancialPoint With {
                             .Date = fpFirst.Date,
                             .Open = fpFirst.Open,
                             .High = fpMax.High,
                             .Low = fpMin.Low,
                             .Close = fpLast.Close
                         }), T)
                         End Function
        ElseIf GetType(T) Is GetType(FinancialPointI) Then
            getY = Function(p) DirectCast(CObj(p), FinancialPointI).High
            getX = Function(p) CLng(DirectCast(CObj(p), FinancialPointI).Coordinate.SecondaryValue)
            clonePoint = Function(firstP, minP, maxP)
                             Dim fpFirst = DirectCast(CObj(firstP), FinancialPointI)
                             Dim fpMin = DirectCast(CObj(minP), FinancialPointI)
                             Dim fpMax = DirectCast(CObj(maxP), FinancialPointI)
                             Dim fpLast = DirectCast(CObj(maxP), FinancialPointI)
                             Return DirectCast(CObj(New FinancialPointI With {
                             .Coordinate = fpFirst.Coordinate,
                             .Open = fpFirst.Open,
                             .High = fpMax.High,
                             .Low = fpMin.Low,
                             .Close = fpLast.Close
                         }), T)
                         End Function
        ElseIf GetType(T) Is GetType(DateTimePoint) Then
            getY = Function(p) DirectCast(CObj(p), DateTimePoint).Value
            getX = Function(p) DirectCast(CObj(p), DateTimePoint).DateTime.Ticks
        ElseIf GetType(T) Is GetType(ObservablePoint) Then
            getY = Function(p) DirectCast(CObj(p), ObservablePoint).Y
            getX = Function(p) CLng(DirectCast(CObj(p), ObservablePoint).X)
        ElseIf GetType(T) Is GetType(LogPoint) Then
            getY = Function(p) DirectCast(CObj(p), LogPoint).Y
            getX = Function(p) CLng(DirectCast(CObj(p), LogPoint).X)
        ElseIf GetType(T) Is GetType(ObservableValue) Then
            getY = Function(p) DirectCast(CObj(p), ObservableValue).Value
            getX = Function(p) CLng(DirectCast(CObj(p), ObservableValue).Coordinate.SecondaryValue)
        Else
            Throw New InvalidOperationException("Unsupported point type: " & GetType(T).Name)
        End If

        Dim i As Integer = 0
        While i < count
            Dim batchEnd As Integer = Math.Min(i + batchSize, count)
            Dim minIndex As Integer = i
            Dim maxIndex As Integer = i
            Dim minY As Double = getY(points(i))
            Dim maxY As Double = minY

            ' Find min and max Y in this batch
            For j As Integer = i To batchEnd - 1
                Dim y = getY(points(j))
                If y < minY Then
                    minY = y
                    minIndex = j
                ElseIf y > maxY Then
                    maxY = y
                    maxIndex = j
                End If
            Next

            Dim pMin = points(minIndex)
            Dim pMax = points(maxIndex)

            ' Keep chronological order
            If getX(pMin) < getX(pMax) Then
                result.Add(pMin)
                result.Add(pMax)
            Else
                result.Add(pMax)
                result.Add(pMin)
            End If

            i += batchSize
        End While

        Return result
    End Function


    Function DownsampleCandlestickToPoints(Of T)(
                    candleSeries As IEnumerable(Of FinancialPoint),
                    maxPoints As Integer,
                    selector As Func(Of FinancialPoint, Double),
                    pointFactory As Func(Of DateTime, Double, T)
                ) As List(Of T)

        If candleSeries Is Nothing OrElse Not candleSeries.Any() Then Return New List(Of T)
        If maxPoints <= 0 OrElse candleSeries.Count() <= maxPoints Then Return candleSeries.Select(Function(p) pointFactory(p.Date, selector(p))).ToList()

        Dim bucketSize = Math.Max(1, Math.Floor(candleSeries.Count() / maxPoints))
        Dim result As New List(Of T)

        For i = 0 To candleSeries.Count() - 1 Step bucketSize
            Dim bucket = candleSeries.Skip(i).Take(bucketSize).ToList()
            If bucket.Count = 0 Then Continue For

            Dim avgValue = bucket.Average(selector)
            Dim midTime = bucket(bucket.Count \ 2).Date

            result.Add(pointFactory(midTime, avgValue))
        Next

        Return result
    End Function

    Function DownsampleCandlestickToObservableValues(
                    candleSeries As IEnumerable(Of FinancialPointI),
                    maxPoints As Integer,
                    selector As Func(Of FinancialPointI, Double)
                ) As List(Of ObservableValue)

        Dim result As New List(Of ObservableValue)
        If candleSeries Is Nothing OrElse Not candleSeries.Any() Then Return result

        Dim total = candleSeries.Count()
        If maxPoints <= 0 OrElse total <= maxPoints Then
            Return candleSeries.Select(Function(p) New ObservableValue(selector(p))).ToList()
        End If

        Dim bucketSize = Math.Max(1, Math.Floor(total / maxPoints))

        For i = 0 To total - 1 Step bucketSize
            Dim bucket = candleSeries.Skip(i).Take(bucketSize).ToList()
            If bucket.Count = 0 Then Continue For

            Dim avgValue = bucket.Average(selector)
            result.Add(New ObservableValue(avgValue))
        Next

        Return result
    End Function