An utility to measure screen area in pixels

Screenshot - PixelMeter.jpg

Introduction

This is an utility with which you can measure an area on the desktop. It can be useful if you, for example, want to know the size of a picture.

Using the Code

The application consists of two windows: the "measurer" and then another that displays the current size of the measuring area.

The measuring window can be resized by dragging the borders and corners.

It can be moved by gripping the tiny red line with the mouse and dragging it around. Since it is only 1 pixel wide, a steady hand is needed.

The code for this is:

If e.Button = MouseButtons.Left Then
   ReleaseCapture()
   SendMessage(CType(Me.Handle.ToInt32, IntPtr), _
               WM_NCLBUTTONDOWN, HTCAPTION, 0&)
End If

It can also be moved by the arrow keys. The window gets into "keyboard move mode" by right clicking the brown border. The code for this is adapted from a VB6 version I did years ago: http://www.vb-helper.com/howto_move_form_with_arrows.html.

Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
  Dim skip_it As Boolean
  If m.Msg = WM_NCRBUTTONDOWN Then
     Select Case m.WParam.ToInt32
        Case HTBORDER, HTBOTTOM, _
          HTBOTTOMLEFT, HTBOTTOMRIGHT, _
          HTLEFT, HTRIGHT, HTTOP, _
          HTTOPLEFT, HTTOPRIGHT, HTGROWBOX
           ' Move the form.
           SendMessage(Me.Handle, WM_SYSCOMMAND, SC_MOVE, 0&)
           skip_it = True
     End Select
  End If
  If Not skip_it Then ' Call the original WindowProc.
     MyBase.WndProc(m)
  End If
End Sub

I would be very grateful for suggestions of improvement here.

Points of Interest

The viewport creation is done like this:

Dim hRgn As IntPtr
Dim hRgnClient As IntPtr

'forms dimensions
lFormWidthPixels = Me.Width
lFormHeightPixels = Me.Height

'get border and title thickness
mlBorderThickness = CInt((lFormWidthPixels - Me.ClientSize.Width) / 2)
mlTitleThickness = CInt((Me.lFormHeightPixels - _
                   Me.ClientSize.Height)) - (2 * mlBorderThickness)

'get viewport dimensions 
lViewportWidthPixels = lFormWidthPixels - (2 * mlBorderThickness)
lViewportHeightPixels = lFormHeightPixels - _
                        mlTitleThickness - (2 * mlBorderThickness)

'get handle
hRgn = CreateRectRgn(0, 0, lFormWidthPixels, lFormHeightPixels)
hRgnClient = _
CreateRectRgn(mlBorderThickness + 1, mlBorderThickness + 1, _
Me.ClientSize.Width + mlBorderThickness - 1, _
Me.ClientSize.Height + mlBorderThickness - 1)

'combine regions
CombineRgn(hRgn, hRgn, hRgnClient, RGN_DIFF)
DeleteObject(hRgnClient)

'set region
SetWindowRgn(Me.Handle, hRgn, -1)
DeleteObject(hRgn)