Vb 2010 graphics.drawline

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I am writing a small screen saver program to draw lines on screen using a timer.
For this, two data points A & B are read from a file and the (x,y) coordinates in pixels for A & B computed.
The line from point A to B is drawn using graphics.drawline method. So far it works fine.
The next line from point B to C is drawn similarly.
The problem is that when line BC is drawn, the line AB is not retained onscreen.
How can I draw line segments BC, CD, DE and so on using a timer while retaining the previous ones ?
I am using VB 2010.

Essentially, I'm drawing a line made up of numerous segments, where each segment is to to be drawn using timer tick event.

What I have tried:

I've tried without using 'refresh' in the timer.tick sub.

here's the code

Imports Microsoft.Win32
Imports Microsoft.VisualBasic
Imports System.Math
Imports System.Drawing.Drawing2D

Public Class frmscr
    Dim greenPen2 As New Pen(Color.Green, 5)
    Dim grayPen1 As New Pen(Color.Gray, 1)

    Dim WithEvents tmrClock As New Timer

    Public point1 As New Point
    Public point2 As New Point

    Private Sub frmscr_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        'Read input data file,reads array of GR
        Call ReadTxtInputFile()

        'Get screen size in pixels
        scrW = Screen.PrimaryScreen.Bounds.Width.ToString
        scrH = Screen.PrimaryScreen.Bounds.Height.ToString
        Windows.Forms.Cursor.Hide()

        'initialize variable i
        i = 1

        'Compute screen x,y of start point in pixels
        'where xo1p is x offset in pixels
        'gr(0) is 1st point of array
        't1Wp is width of 1st vertical track
        'grmax & grmin are max & min values of parameter array value gr(i)
        xGR0 = xo1p + t1Wp * (GR(0) - GRmin) / (GRmax - GRmin)
        yGR0 = 0

        'set initial values of second point & its backup value
        xGR1 = xGR0
        xGR2 = xGR0
        yGR1 = yGR0
        yGR2 = yGR0


        ' Set Pen Styles
        greenPen2.DashStyle = Drawing2D.DashStyle.Solid
        grayPen1.DashStyle = Drawing2D.DashStyle.DashDotDot

        'timer
        tmrClock.Enabled = True
        tmrClock.Interval = 50
        tmrClock.Start()


    End Sub

    Private Sub frmscr_FormClosing(sender As Object, e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        Windows.Forms.Cursor.Show()
    End Sub

    Private Sub frmscr_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
        Me.Close()
    End Sub

    Private Sub frmscr_KeyPress(sender As Object, e As System.Windows.Forms.KeyPressEventArgs) Handles Me.KeyPress
        Me.Close()
    End Sub

    Private Sub frmscr_MouseClick(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseClick
        Me.Close()
    End Sub

    Private Sub frmscr_MouseDoubleClick(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDoubleClick
        Me.Close()
    End Sub

    Private Sub frmscr_MouseMove(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
        Static OldX As Integer
        Static OldY As Integer
        'Determines whether the mouse was moved and whetherthe movement was large.
        ''If so, the screen saver is ended.
        If (OldX > 0 And OldY > 0) And (Math.Abs(e.X - OldX) > 3 Or Math.Abs(e.Y - OldY) > 3) Then
            Me.Close()
        End If
        ''Assigns the current X and Y locations to OldX and OldY.
        OldX = e.X
        OldY = e.Y
    End Sub
    Private Sub DrawGrids(ByVal e As PaintEventArgs)

        ' Define Vertical grid points : track width in % : default values
        t1W = 15

        'track width in pixels
        t1Wp = t1W * scrW / 100

        'track x offset in pixels
        xo1p = 0


        ' Create points that define line.
        'vertical grid
        Dim ii As Integer

        For ii = 1 To 4 Step 1
            Dim point1 As New Point(t1Wp / 10 * ii, 0)
            Dim point2 As New Point(t1Wp / 10 * ii, scrH)
            e.Graphics.DrawLine(grayPen1, point1, point2)
        Next ii
        For ii = 6 To 9 Step 1
            Dim point1 As New Point(t1Wp / 10 * ii, 0)
            Dim point2 As New Point(t1Wp / 10 * ii, scrH)
            e.Graphics.DrawLine(grayPen1, point1, point2)
        Next ii

        For ii = 0 To 10 Step 5
            Dim point1 As New Point(t1Wp / 10 * ii, 0)
            Dim point2 As New Point(t1Wp / 10 * ii, scrH)
            e.Graphics.DrawLine(Pens.Blue, point1, point2)
        Next ii


        'horizontal grid
        nhThk = scrH / 75


        For ii = 1 To nhThk Step 1
            Dim point1 As New Point(0, 75 * ii)
            Dim point2 As New Point(t1Wp, 75 * ii)

            e.Graphics.DrawLine(grayPen1, point1, point2)
        Next ii

    End Sub


    Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)

        e.Graphics.SmoothingMode = SmoothingMode.HighQuality

        'routine to draw the grid
        DrawGrids(e)

        'routine to draw the curve
        DrawCurve(e)

    End Sub

    Private Sub DrawCurve(ByVal e As PaintEventArgs)

        e.Graphics.DrawLine(greenPen2, xGR1, yGR1, xGR2, yGR2)

        'stores 
        xGR1 = xGR2
        yGR1 = yGR2

        'clear screen after line reaches screen bottom
        If i >= (scrH / 3.75) - 1 Then
            i = 1

            ClearForm(e)

            yGR1 = 0

        End If
    End Sub

    Private Sub ClearForm(ByVal e As PaintEventArgs)
        'To clear the screen before continuing drawing
        e.Graphics.Clear(Color.Black)
    End Sub

    Private Sub tmrClock_Tick(ByVal sender As System.Object,
     ByVal e As System.EventArgs) Handles tmrClock.Tick

        'increment variable i to compute screen location of next point
        i = i + 1

        'computes screen location (x,y) of next point 
        xGR2 = xo1p + t1Wp * (GR(i) - GRmin) / (GRmax - GRmin)
        yGR2 = (DEPT(i) - DepthFirst) * 25

        Refresh()
    End Sub

End Class

Posted 20-Feb-17 21:24pm

Member 10118655

Updated 28-Feb-17 14:13pm

v3

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Comments

Graeme_Grant 21-Feb-17 3:42am

We are not here to write your code for you. How can we can help you if you don't show us what you have tried...

Richard MacCutchan 21-Feb-17 3:55am

Ensure that you draw all lines within the same iteration of the paint routine.

Ralf Meier 27-Feb-17 5:39am

I have seen your code.
My Question : where are all your Variables definded ?
Have you tried to work without the method "ClearForm" in DrawCurve ?

Member 10118655 27-Feb-17 12:38pm

All my variables are defined as public in a separate module.
Yes, I've tried it without 'ClearForm' method.

Ralf Meier 27-Feb-17 14:37pm

OK ... then provide this code-part too ...
Then I could simulate what is going on ...

Member 10118655 28-Feb-17 12:40pm

Module PubVar 'Declare variables & constants
Public Const inFile = "E:\testdata\test.txt"
Public Const ILDmin = 0.1, ILDmax = 100, RHOBmin = 1.8, RHOBmax = 2.8, NPHImin = -0.06, NPHImax = 0.54, SPmin = 20, SPmax = 120
Public Const BSmin = 6, BSmax = 16, CALImin = 6, CALImax = 16, DTmin = 40, DTmax = 140, GRmin = 0, GRmax = 150
Public DEPT(100000), BS(100000), CALI(100000), DT(100000), GR(100000), ILD(100000), RHOB(100000), NPHI(100000), SP(100000) As Double
Public DepthTopFile, DepthBotFile As Double
Public DepthFirst, DepthLast As Double
Public NumRec As Long
Public scrW, scrH As Integer 'screen width & height
Public t1W, t2W, t3W, t4W, t5W, t6W, tdW, ttw As Integer 'track width in %
Public t1Wp, t2Wp, t3Wp, t4Wp, t5Wp, t6Wp, tdWp As Integer 'track width in pixels
Public xoDp, xo1p, xo2p, xo3p, xo4p, xo5p, xo6p As Integer 'track x-offset in pixels
Public nhThn, nhMed, nhThk As Integer 'no. of horizontal thick & thin lines
Public nDec As Integer 'no of decades in resistivity scale
Public xGR0, xGR1, xGR2, yGR0, yGR1, yGR2 As Single
Public i, j, iScr, numScr As Integer
End Module

Ralf Meier 28-Feb-17 15:01pm

OK ... I tested your code and looked with the Debugger which results appear.
In my Test the calculation for XGr2 and YGr2 (done with each Timer-Tick) results allways the same result - 0.0
Where are the other Variables calculated which you use for the both multiplications - all those are 0.0 too ...

Member 10118655 1-Mar-17 12:02pm

My data looks like this where array in 1st column is 'Depth' & 2nd column is 'GR'. The values of XGR2, YGR2 are computed ok. I've tried it out. Another module reads these from a disk file 'test.txt' into the arrays 'DEPT' & 'GR'.
--------------------------------------------------------
2423.9220 85.9
2424.0744 83.9
2424.2268 77.8
2424.3792 73.6
2424.5316 74.2
2424.6840 75.9
2424.8364 75.7
2424.9888 75.1
2425.1412 77.2
2425.2936 80.8
2425.4460 84.0
2425.5984 87.4
2425.7508 90.0
2425.9032 89.9
2426.0556 87.5
2426.2080 86.1
2426.3604 86.4
2426.5128 86.9
2426.6652 86.9
2426.8176 86.0
2426.9700 84.6
2427.1224 84.4
2427.2748 86.5
2427.4272 88.7
2427.5796 89.8
.....
.....

Graeme_Grant 1-Mar-17 20:48pm

Solution 2 fixes your problem.

2 solutions

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Graeme_Grant · Answer 1 · 2017-02-27T21:10:00

Here is a working mock:

VB

Imports System.Drawing.Text

Public Class Form1
    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        Refresh()
    End Sub

    Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
        DrawLines(e.Graphics)
    End Sub

    Dim r As Random = New Random()
    Dim pens As Pen() = New Pen(4) _
        {
            New Pen(Brushes.Blue),
            New Pen(Brushes.Red),
            New Pen(Brushes.Green),
            New Pen(Brushes.Cyan),
            New Pen(Brushes.Purple)
        }

    Private Sub DrawLines(ByVal gr As Graphics)

        gr.TextRenderingHint = TextRenderingHint.AntiAlias

        For i As Integer = 1 To 5
            gr.DrawLine(pens(r.Next(0, 4)), r.Next(0, 200), r.Next(0, 200), r.Next(0, 200), r.Next(0, 200))
        Next

    End Sub

End Class

I suggest that there is an issue with your code.

Graeme_Grant · Answer 2 · 2017-02-28T14:13:00

"where each segment is to to be drawn using timer tick event" - The issue is that you're not retaining a snapshot of the graphics object and adding to it but drawing on a new graphics object each time. This is why you don't see any drawing history. (copy of answer from Solution 1 comments).

Here is a modified version of Solution 1:

VB

Imports System.Drawing.Imaging
Imports System.Drawing.Text

Public Class Form1



    Private myBitmap As Bitmap

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        Refresh()
    End Sub

    Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
        DrawLines(e.Graphics)
    End Sub

    Dim r As Random = New Random()
    Dim pens As Pen() = New Pen(4) _
        {
            New Pen(Brushes.Blue),
            New Pen(Brushes.Red),
            New Pen(Brushes.Green),
            New Pen(Brushes.Cyan),
            New Pen(Brushes.Purple)
        }

    Private Sub DrawLines(ByVal gr As Graphics)

        Dim myG As Graphics

        If myBitmap Is Nothing Then
            myBitmap = New Bitmap(ClientRectangle.Width, ClientRectangle.Height, PixelFormat.Format24bppRgb)
            myG = Graphics.FromImage(myBitmap)
            myG.Clear(Color.Black)
        Else
            myG = Graphics.FromImage(myBitmap)
        End If

        myG.TextRenderingHint = TextRenderingHint.AntiAlias
        myG.DrawLine(pens(r.Next(0, 4)), r.Next(0, 200), r.Next(0, 200), r.Next(0, 200), r.Next(0, 200))

        gr.DrawImage(myBitmap, 0, 0, myBitmap.Width, myBitmap.Height)

        myG.Dispose()

    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        BackColor = Color.Black
    End Sub
End Class