Making drawn lines stay on screen

[Gluttard]

Hey, I'm hoping that you guys can help me on this, I could probably find the answer if I probed hard enough but I'm a beginner and I don't know what keywords to search for, so maybe if you answer this you could help me out with that too.

I made a drawing application that draws lines, you click down and it records where your mouse is and draws a line to where you 'unclick' the mouse. Whenever I draw a new line, the previous one disappears, so I want to know how I can prevent this.

    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
            e.Graphics.DrawLine(Color, PointX1, PointY1, PointX2, PointY2)
    End Sub

That draws the line (I took out some unrelated information), so maybe after it draws it could I store all of the lines drawn and then re-draw them after I make a new one?
Any help would be great.

 

[DiskJunky]

you'll need to store all the points of all the lines and redraw them each time in the Paint event. Tedious but necessary...

 

[JohnH]

Another way: each time you draw a new line draw it to an image, display this image.

 

[Gluttard]

Another way: each time you draw a new line draw it to an image, display this image.

What code do I use to draw it to an image?

 

[JohnH]

Graphics.FromImage method.

Dim r As New Random
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
    If Me.BackgroundImage Is Nothing Then
        Me.BackgroundImage = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height)
    End If
    Dim bmp As New Bitmap(Me.BackgroundImage)
    Dim g As Graphics = Graphics.FromImage(bmp)
    Dim pt1 As New Point(r.Next(0, bmp.Width), r.Next(0, bmp.Height))
    Dim pt2 As New Point(r.Next(0, bmp.Width), r.Next(0, bmp.Height))
    g.DrawLine(Pens.Blue, pt1, pt2)
    g.Dispose()
    Me.BackgroundImage = bmp
End Sub

 

[Gluttard]

I'm sorry, but I just can't figure this out myself.
Where do I put the code pictured above? Here's what I have right now:

Public Class Form1
    Dim PointX1 As Integer
    Dim PointX2 As Integer
    Dim PointY1 As Integer
    Dim PointY2 As Integer
    Dim Color As Pen = Pens.Black
    Dim Ready1 As Integer = 0
    Dim Ready As Integer = 0
    Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
        Timer1.Enabled = True
        If Black.Checked = True Then
            Color = Pens.Black
        End If
        If Red.Checked = True Then
            Color = Pens.Red
        End If
        If Green.Checked = True Then
            Color = Pens.Green
        End If
        If White.Checked = True Then
            Color = Pens.White
        End If
        If Blue.Checked = True Then
            Color = Pens.Blue
        End If
        If Purple.Checked = True Then
            Color = Pens.Purple
        End If
        PointX1 = Cursor.Position.X - Me.Location.X - 4
        PointY1 = Cursor.Position.Y - Me.Location.Y - 30
    End Sub

    Private Sub Form1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseUp
        Timer1.Enabled = False
        PointX2 = Cursor.Position.X - Me.Location.X - 4
        PointY2 = Cursor.Position.Y - Me.Location.Y - 30
        Ready1 = 1
        Me.Refresh()
    End Sub

    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
        If Ready1 = 1 Then
            e.Graphics.DrawLine(Color, PointX1, PointY1, PointX2, PointY2)
            Ready1 = 0
        End If
    End Sub

    Private Sub Timer2_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer2.Tick
        Label1.Text = Cursor.Position.X - Me.Location.X - 3 & " , " & Cursor.Position.Y - Me.Location.Y - 30
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        Ready = 1
        Me.Refresh()
    End Sub

    Private Sub Form1_RubberPaint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
        If Ready = 1 Then
            e.Graphics.DrawLine(Color, PointX1, PointY1, Cursor.Position.X - Me.Location.X - 3, Cursor.Position.Y - Me.Location.Y - 31)
            Ready = 0
        End If
    End Sub
End Class

Eh that might be tough to look through, but the general gist of it is that I want to draw a line, store everything drawn as 'bmp' and then when I draw another line, i'll display that bmp and have everything appear...
Right now it draws a line, then the first line vanishes and a new one is drawn.

 

[JohnH]

MouseUp event is where you have provided yourself a new line, this is where you have to take action.

 

[myblueocean]

Um, when you program colours or shapes don't they stay on the form? While debugged of course?

 

[JohnH]

Um, when you program colours or shapes don't they stay on the form? While debugged of course?

When you program something it does exactly what you have specified.

 

[Gluttard]

Okay, now how do I convert an integer into a point?
I want to get the cursor position relative to the bitmap stored as a point, but how do I do that? It gives me an error if I try and put:

Dim Point1X as new point
...
...
Point1X = Cursor.Position.X - Me.Location.X

 

[JohnH]

A Point is a coordinate system value, it has X and Y properties.

dim pt as point = cursor.position
pt.X+=1
pt.Y-=123

Anyway, use e parameter of the mouse events to get the coordinate values. There is e.Location and also e.X/e.Y should you only need one of these, but they are the same as e.Location.X/Y. These coordinates are relative to the client area of the control.