How to Erase a Line created using .DrawLine

Question

How to Erase a Line created using .DrawLine

raklali 236

On a PictureBox I have drawn Several ellipses and lines. One Line originates (X1,Y1) from centre of PictureBox1 and extends till certain range (length-X2,Y2). Using a Slider/HScrollBar I want to redraw this line by assgining New Values to the X2, Y2 and also erase the line drawn using Old/ original X2,Y2.

The Old Line remains partially visible. On refreshing or invalidating the PictureBox1, all other drawn objects disaappear.

Can someone help?

Castorix31 90,686 Reputation points

2022-01-16T09:13:05.403+00:00

Not sure if it is something like this test :

raklali 236

I tried this

  Dim myPath As New GraphicsPath
    myPath.AddLine(CInt(P2.X), CInt(P2.Y), CInt(P1.X), CInt(P1.Y))
    Dim myPen As New Pen(Color.Red, 2)
    With PictureBox1.CreateGraphics()
        .DrawPath(myPen, myPath)
    End With

But am the old Line Remains

@Castorix, May I once again request for the code..

Thank you

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Castorix31 90,686 Reputation points

2022-01-16T09:13:05.403+00:00

Not sure if it is something like this test :
raklali 236 Reputation points

2022-01-16T09:47:18.37+00:00

I tried this

Dim myPath As New GraphicsPath myPath.AddLine(CInt(P2.X), CInt(P2.Y), CInt(P1.X), CInt(P1.Y)) Dim myPen As New Pen(Color.Red, 2) With PictureBox1.CreateGraphics() .DrawPath(myPen, myPath) End With

But am the old Line Remains

@Castorix, May I once again request for the code..

Thank you

Answer 1

Castorix31 90,686

From comments, the test code I did, with a similar method as LesHay-2099 described, with a List of lines (Segment Class) :
(PictureBox and Scrollbars added from Design Mode)

Public Class Form1

    'Method from http://csharphelper.com/blog/2018/12/let-the-user-draw-lines-in-c/

    Private Segments As List(Of Segment) = New List(Of Segment)()
    Private NewSegment As Segment = Nothing

    Private SpecialSegment As Segment = Nothing
    Private ptOrigin As Point = Nothing
    Private ptDest As Point = Nothing

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        ptOrigin = New Point(CInt(PictureBox1.ClientSize.Width / 2), CInt(PictureBox1.ClientSize.Height / 2))
        ptDest = New Point(CInt(PictureBox1.ClientSize.Width / 2), CInt(PictureBox1.ClientSize.Height / 2))
        SpecialSegment = New Segment(Pens.Red, ptOrigin, ptDest)
        Segments.Add(SpecialSegment)
        HScrollBar1.Minimum = -CInt(PictureBox1.ClientSize.Width / 2)
        HScrollBar1.Maximum = CInt(PictureBox1.ClientSize.Width / 2) + HScrollBar1.LargeChange - 1
        HScrollBar2.Minimum = -CInt(PictureBox1.ClientSize.Height / 2)
        HScrollBar2.Maximum = CInt(PictureBox1.ClientSize.Height / 2) + HScrollBar2.LargeChange - 1
    End Sub

    Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown
        NewSegment = New Segment(Pens.Blue, e.Location, e.Location)
        PictureBox1.Refresh()
    End Sub

    Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint
        e.Graphics.Clear(PictureBox1.BackColor)
        e.Graphics.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias
        For Each segment As Segment In Segments
            segment.Draw(e.Graphics)
        Next
        If NewSegment IsNot Nothing Then NewSegment.Draw(e.Graphics)
    End Sub

    Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
        If NewSegment Is Nothing Then Return
        NewSegment.pt2 = e.Location
        PictureBox1.Refresh()
    End Sub

    Private Sub PictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp
        If NewSegment Is Nothing Then Return
        NewSegment.pen1 = Pens.Black
        Segments.Add(NewSegment)
        NewSegment = Nothing
        PictureBox1.Refresh()
    End Sub

    Private Sub HScrollBar1_Scroll(sender As Object, e As ScrollEventArgs) Handles HScrollBar1.Scroll
        ptDest.X = ptOrigin.X + e.NewValue
        SpecialSegment.pt2 = ptDest
        PictureBox1.Refresh()
    End Sub

    Private Sub HScrollBar2_Scroll(sender As Object, e As ScrollEventArgs) Handles HScrollBar2.Scroll
        ptDest.Y = ptOrigin.Y + e.NewValue
        SpecialSegment.pt2 = ptDest
        PictureBox1.Refresh()
    End Sub
End Class

Class Segment
    Public pen1 As Pen
    Public pt1, pt2 As Point

    Public Sub New(pen As Pen, point1 As Point, point2 As Point)
        pen1 = pen
        pt1 = point1
        pt2 = point2
    End Sub

    Public Sub Draw(gr As Graphics)
        gr.DrawLine(pen1, pt1, pt2)
    End Sub
End Class

raklali 236

I too got it, Almost....

Imports System.Drawing.Drawing2D

Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        AddPathExample()
    End Sub
    Public Sub AddPathExample()
        'Dim e As PaintEventArgs
        With PictureBox1.CreateGraphics()

            ' Creates a symetrical triangle and adds an inverted triangle.

            ' Create the first path - right side up triangle.
            Dim myArray As Point() = {New Point(20, 20), New Point(HScrollBar1.Value, HScrollBar1.Value)}
            Dim myPath As New GraphicsPath
            myPath.AddLines(myArray)




            ' Draw the combined path to the screen.
            Dim myPen As New Pen(Color.Black, 2)
            .DrawPath(myPen, myPath)

        End With

    End Sub



    Private Sub HScrollBar1_Scroll(sender As Object, e As ScrollEventArgs) Handles HScrollBar1.Scroll
        AddPathExample()
    End Sub
End Class

Thank you again.

raklali 236 Reputation points

2022-01-18T01:52:49.807+00:00

Hi @Castorix31 , I think I missed it out in my question. How do we Hide the Red Line that is drawn in this example? Thank you
Castorix31 90,686 Reputation points

2022-01-18T06:50:15.667+00:00
You can just remove it from the List
In my test, I added it at beginning, so :

Segments.RemoveAt(0) PictureBox1.Refresh()
raklali 236 Reputation points

2022-01-18T12:33:21.903+00:00

Wow, Thanks... and I was looking for changing the Color to the Parent Color...
Simple tech... Thanks sir.

I think, I will bother you on the Graphics management.... I will try first and If I fail, I request your help.
raklali 236 Reputation points

2022-01-23T14:22:30.14+00:00

Hi @Castorix31 and @LesHay , A small query. All the Drawings are working fine. But one point the PictureBox1 get cluttered. Is it possible to clear PictureBox1 of all drawings in One Click() of Button?
LesHay 7,141 Reputation points

2022-01-23T16:27:13.89+00:00

Hi

PictureBox1.Image = Nothing
raklali 236 Reputation points

2022-01-24T01:21:07.143+00:00

I tried that but it doesn't work..
LesHay 7,141 Reputation points

2022-01-24T05:39:42.837+00:00

Hi
Well, it does work, but you probably didn't ask the correct question. You likely meant how to delete all grahips shapes etc.
If that is the case then just set the collection to 'Nothing' and call 'Invalidate on the PictureBox'.
raklali 236 Reputation points

2022-01-24T12:53:12.217+00:00

Maybe, What I did was Segments.ClearAll under a Button1_Click() and then called a Private Sub` to create new Shapes again. That did the trick. But Thank you sir.

Answer 2

Hi

Personally, I would use GraphicsPaths for doing this. I would create a new GraphicsPath for each element I want to draw, and and add each to a collection of GraphicsPath.
The Paint event would loop the collection and draw each element. So, to erase an element it is as simple as removing it from the collection. Adding elements is just as straightforward by adding to the collection.
Another benefit is that you can add/remove all sorts of shapes etc just as easily.
If needed, the idea is easily expanded to have separate colors/pen widths etc for each element - this could be accomplished by creating a Class with the GraphicsPath and the various factors such as pen with, fill color, outline color etc - and adding new instances of the Class to a collection. In the Paint ebent, just draw the path using the various factors stored for each element in the Class instance.

But, see Castorix suggestion for more advance cases.

raklali 236 Reputation points

2022-01-16T09:46:04.65+00:00

@Anonymous , May I once again request for the code.

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How to Erase a Line created using .DrawLine

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