Drawing large amount lines .net

Question 1

here the code block that optimizes the graph automatically, it does not help for many small waveforms, but it works wonders on the 10k and larger ones:

Private Function Calculate3(ByVal aData()() As Double, ByVal AmplitudeUsed As Double, ByVal OffsetUsed As Double, ByVal LengthUsed As Integer) As Bitmap
    Dim PS_Y As Double

    'Instead of making this random, here a real calculation for the scale (chartheight / biggest waveform amplitude) :
    PS_Y = 600 / (AmplitudeUsed * 2 + AmplitudeUsed * 0.1)  ' Rnd() + 0.1

    'Since our calculation method oscillates around zero with the same amplitude we can predict that we need the following offset:
    Dim Origin As PointF = New PointF(0, 300)


    Dim Data(), ST As Double
    Dim lPoints As New List(Of PointF)

    'set the x axis scale to make our waveform fit exactly:
    Dim PS_X As Double = 900 / LengthUsed

    Dim Img As New Bitmap(900, 600)
    Dim ImgGR As Graphics = Graphics.FromImage(Img)
    ImgGR.Clear(Color.White)
    Dim WFPen As New Pen(Brushes.Black, 1)

    'theese 2 values simply define an area in the picture where the waveforms are actually visible to not overlap with the axis / legend, set it to something that makes sense
    Dim l As Integer = 20 'ChartRect.Left
    Dim r As Integer = 700 'ChartRect.Right

    Dim APT() As PointF
    For i = 0 To aData.Length - 1
        Dim iStart As Integer
        Dim iEnd As Integer

        Dim ScaleX As Double
        Dim OrigX As Single

        'Set sampletime to 1 second to keep the predefined scale from above, but still do the calculation as it would be needed with real data:
        ST = 1 ' Rnd()
        Data = aData(i)

        If Data.Length = 0 Then Continue For

        ScaleX = ST * PS_X
        OrigX = Origin.X

        iStart = (l - OrigX) / ScaleX
        iEnd = (r - OrigX) / ScaleX
        If iStart < 0 Then iStart = 0
        If iEnd < 0 Then iEnd = 0
        If iEnd > Data.Length - 1 Then iEnd = Data.Length - 1
        If iStart > Data.Length - 1 Then iStart = Data.Length - 1

        iStart = 0
        iEnd = Data.Length - 1

        If iEnd < iStart Then Continue For

        If ScaleX < 0.3 Then 'more than 3 lines per point, summarize
            Dim iPT As Integer

            Dim FirstX As Integer
            Dim LastX As Integer

            Dim MinY As Single
            Dim MaxY As Single
            Dim tVal As Single

            Dim iSt As Integer
            Dim iEn As Integer


            FirstX = Math.Truncate(iStart * ScaleX)
            LastX = Math.Ceiling(iEnd * ScaleX)

            ReDim APT((LastX - FirstX) * 2 - 1)
            For iX = FirstX To LastX - 1
                MinY = Single.MaxValue
                MaxY = Single.MinValue

                iSt = Math.Truncate(iX / ScaleX)
                iEn = Math.Truncate((iX + 1) / ScaleX) - 1
                If iSt < 0 Then iSt = 0
                If iEn > Data.Length - 1 Then iEn = Data.Length - 1

                For iDat = iSt To iEn
                    tVal = -Data(iDat) * PS_Y
                    If tVal > MaxY Then MaxY = tVal
                    If tVal < MinY Then MinY = tVal
                Next

                iPT = (iX - FirstX) * 2
                APT(iPT) = Origin + New SizeF(iX, MinY)
                APT(iPT + 1) = Origin + New SizeF(iX, MaxY)
            Next


        Else
            ReDim APT(iEnd - iStart)
            For j = iStart To iEnd
                APT(j - iStart) = Origin + New SizeF(j * ScaleX, -(Data(j) * PS_Y))
            Next

        End If




        ImgGR.DrawLines(WFPen, APT)
    Next


    Return Img
End Function

Thank you all for taking your time to read my question

Question 2

You may be able to speed it up by check the distance between points, and skip the ones that are too close to the previous point.

You can skip the sqrt in the distance calculations, and do other optimizations if needed.

To see if this would be beneficial, try running the benchmark using n/2 points.