VB.net 4.5 need help making multiple rectangles on panel

[DougP]

I have this code which draws a rectangle on a panel. It works great.
but it only lets me draw one. I want to be able to draw a lot of them and also save each of their coordinates, and then be able to recreate them. Yes this is a baby drawing program.

    Private Sub Panel1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Panel1.MouseDown
        Rect.Location = e.Location
    End Sub

    Private Sub Panel1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Panel1.MouseMove
        Panel1.Cursor = Cursors.Cross
        If e.Button = MouseButtons.Left Then
            Rect.Size = New Size(e.X - Rect.X, e.Y - Rect.Y)
            Panel1.Invalidate()
        End If
    End Sub

    Private Sub Panel1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Panel1.Paint
        Dim L, T, W, H As Integer
        L = Rect.X : T = Rect.Y
        W = Rect.Width : H = Rect.Height
        If W < 0 Then
            L += W : W = -W
        End If
        If H < 0 Then
            T += H : H = -H
        End If
        e.Graphics.DrawRectangle(Pens.Red, New Rectangle(L, T, W, H))
    End Sub

DougP

 

[jebenson]

You need to use one of the overloaded versions of Invalidate, which takes a Rectangle as the parameter and only repaints that Rectangle:

    Private Sub Panel1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Panel1.MouseMove
        Panel1.Cursor = Cursors.Cross
        If e.Button = MouseButtons.Left Then
            Rect.Size = New Size(e.X - Rect.X, e.Y - Rect.Y)

            [red]Dim RectToInvalidate As Rectangle
            RectToInvalidate = New Rectangle(Rect.X, Rect.Y, Rect.Width + 1, Rect.Height + 1)
            Panel1.Invalidate(RectToInvalidate)
            RectToInvalidate = Nothing[/red]

        End If
    End Sub

I add 1 to the Width and Height of Rect in RectToInvalidate, because just using the measurements of Rect results in the right and bottom lines not to being drawn.

Also:
- any new rectangle will be "over" an old one if the two rectangles overlap, and the one underneath is obscured.
- this method only works well if you drag the cursor down and to the right. Going left and/or up, it doesn't work so well. Run the code and you'll see.

I leave these issues for you to solve.

As for saving the rectangles, you could use an array, list or collection to store rectangles, creating a new one each time the MouseDown event handler fires instead of reusing the single global Rectangle object you have now.

Hope this helps.


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