Dynamically change pen color & paint when clicked - vb.net

Question

The Program
I'm playing around and learning about graphics using visual basic (coming from C++). I've made a program and I want to do two things: paint when the left mouse button is pressed, and stop when released, and also I want to be able to change the pen color using a colordialog. After hours of frustration, I've yet to combat these two problems.
The Code (Snippet)
Private obj As Graphics
Dim rect As Rectangle
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
obj = RichTextBox1.CreateGraphics
End Sub
Private Sub Form1_FormClosed(ByVal sender As System.Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles MyBase.FormClosed
obj.Dispose()
End Sub
Private Sub RichTextBox1_MouseMove(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles RichTextBox1.MouseMove
With rect
.X = e.X
.Y = e.Y
.Width = TrackBar1.Value
.Height = TrackBar1.Value
End With
If ToolStripButton1.Checked = True Then
obj.DrawEllipse(Pens.Black, rect)
ElseIf ToolStripButton2.Checked = True Then
obj.DrawRectangle(Pens.Black, rect)
End If
ToolStripStatusLabel2.Text = (e.X & ", " & e.Y)
End Sub
Past Attempts (and frustrations)
My idea originally was to do this:
Dim myPen = New Pen(ButtonWithDC1.BackColor)
But doing so gave me an error message. I looked at Microsoft's documentation, but it wasn't useful for what I'm trying to do. I can create a pen just fine, but I'd like for the user to be able to change the color while the app is currently running.
GUI Layout
I don't have an attempt at my other problem (drawing while pressing the mouse down, not just by moving the mouse -- like a normal paint program), I don't even have a starting point for that solution. Thanks to everyone in advance.

Answer 1

Place a button (Button1) and picturebox (PictureBox1) on a form, also add a colordialog (ColorDialog1).
This code will allow you to draw on the picture box and choose the color using a color you select from the colordialog. The MouseDown event writes a flag that the mouse is down, and stores the last location. The MouseUp does similar. The MouseMove actually draws. Use a line and the last location.
Public Class Form1
Private myColor As Color = Color.Black
Private mouseIsDown As Boolean = False
Private previousLocation As System.Nullable(Of System.Drawing.Point) = Nothing
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
myColor = If(ColorDialog1.ShowDialog() = Windows.Forms.DialogResult.OK, ColorDialog1.Color, myColor)
End Sub
Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown
mouseIsDown = True
previousLocation = e.Location
End Sub
Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
If mouseIsDown Then
If previousLocation IsNot Nothing Then
Using g As Graphics = Graphics.FromImage(PictureBox1.Image)
g.DrawLine(New Pen(myColor), previousLocation.Value, e.Location)
End Using
PictureBox1.Invalidate()
End If
previousLocation = e.Location
End If
End Sub
Private Sub PictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp
mouseIsDown = False
previousLocation = Nothing
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.PictureBox1.Image = New Bitmap(PictureBox1.Width, PictureBox1.Height)
End Sub
End Class

Answer 2

Your question is a bit more involved than you think, and SO is not keen on multiple questions per post (not in your nest interest either - someone might know A and not B so wont bother answering).
To draw on Mousemove when the mouse is down, you need to track when the mouse is down (question A):
Private _mouseDown As Boolean
Private _mouseLoc As Point
Private _mouseNewLoc As Point
sub Ctl_MouseDown(sender...
' ToDo: add logic to check which button....
_mouseDown = True
_mouseLoc = New Point(e.X, e.Y)
End Sub
sub Ctl_MouseUp(sender...
_mouseDown = False
End Sub
Then mousemove can be used to capture the current location
Sub Ctl_MouseMove(sender....
If _mouseDn Then
_mouseNewLoc = New Point(e.X, e.Y)
Ctl.invalidate ' call to paint
End If
End Sub
' selected color from dialog or whereever
Private myColor As Color
Sub Ctl_Paint(sender....
If _mouseDn Then
' Pen ctor is overloaded...(Question B)
Using p As New Pen(myColor)
e.Graphics.DrawLine(p, _mouseLoc, _mouseNewLoc)
' plus more....
End Using
End If
This only addresses the questions posed; the bigger issue you have is tracking what has already been drawn. This will draw a line only while the mouse is down, but for a polygon or shape, you have to add code to redraw those parts. Either a List of the points which make up a polygon, or maybe save what you have to a bitmap and add to it. Thats a bit outside the scope of the question and depends on app factors. You also need a Drawing start/stop or way to signal when to stop adding lines or ovals or whatever (ovals are sort of simple: one at a time, lines as part of a shape will take some work).
Either way all painting has to take place in the Paint event (or OnPaint) if you want to see the shape/drawing/image develop.