How to Create Rubber-Band Lines/Boxes in Visual Basic

• Standard and Professional Editions of Microsoft Visual Basic for Windows, versions 2.0 and 3.0
• Microsoft Visual Basic programming system for Windows, version 1.0

SUMMARY

Creating rubber bands within Visual Basic can be done using the DrawMode property. Rubber bands are lines that stretch as you move the mouse cursor from a specified point to a new location. This can be very useful in graphics programs and when defining sections of the screen for clipping routines.

MORE INFORMATION

The theory of drawing a rubber-band box is as follows:

1. Draw a line from the initial point to the location of the mouse cursor using:

         [form].DrawMode = 6. {INVERT}
   

2. Move the mouse cursor.

3. Save the DrawMode.

4. Set the [form].DrawMode to 6. {INVERT}

5. Draw the same line that was drawn in step 1. This will restore the image underneath the line.

6. Set the [form].DrawMode back to the initial DrawMode saved in step 3.

7. Repeat the cycle again.

The sample below will demonstrate the rubber-band line and the rubber-band box. Clicking the command buttons will allow the user to select between rubber-band line or a rubber-band box. The user will also be able to select a solid line or a dashed line.

Create and set the following controls and properties:

   Control Name   Caption      Picture
   ------------------------------------------------
   Form1          Form1        c:\windows\chess.bmp
   Command1       RubberBand
   Command2       RubberBox
   Command3       Dotted
   Command4       Solid

Const INVERSE = 6       '*Characteristic of DrawMode property(XOR).
Const SOLID = 0         '*Characteristic of DrawStyle property.
Const DOT = 2           '*Characteristic of DrawStyle property.

In the appropriate procedures, add the following code:

Sub Form_MouseDown (Button As Integer, Shift As Integer, X As
                                       Single, Y As Single)
   '* Store the initial start of the line to draw.
   StartX = X
   StartY = Y

   '* Make the last location equal the starting location
   OldX = StartX
   OldY = StartY
End Sub

Sub Form_MouseMove (Button As Integer, Shift As Integer, X As
                      Single, Y As Single)
   '* If the button is depressed then...
   If Button Then
      '* Erase the previous line.
      Call DrawLine(StartX, StartY, OldX, OldY)

      '* Draw the new line.
      Call DrawLine(StartX, StartY, X, Y)

      '* Save the coordinates for the next call.
      OldX = X
      OldY = Y
   End If
End Sub

Sub DrawLine (X1, Y1, X2, Y2 As Single)
   '* Save the current mode so that you can reset it on
   '* exit from this sub routine. Not needed in the sample
   '* but would need it if you are not sure what the
   '* DrawMode was on entry to this procedure.
   SavedMode% = DrawMode

   '* Set to XOR
   DrawMode = INVERSE

   '*Draw a box or line
   If DrawBox Then
      Line (X1, Y1)-(X2, Y2), , B
   Else
      Line (X1, Y1)-(X2, Y2)
   End If

   '* Reset the DrawMode
   DrawMode = SavedMode%
End Sub

Sub Form_MouseUp (Button As Integer, Shift As Integer, X As Single,
                  Y As Single)
   '* Stop drawing lines/boxes.
   StartEvent = FALSE
End Sub

Sub Command2_Click ()
   '* Boolean value to determine whether to draw a line or box.
   DrawBox = TRUE
End Sub

Sub Command1_Click ()
   '* Boolean value to determine whether to draw a line or box.
   DrawBox = FALSE
End Sub

Sub Command3_Click ()
   '* Create a dotted line
   Form1.DrawStyle = DOT
End Sub

Sub Command4_Click ()
   '* Create a solid line.
   Form1.DrawStyle = SOLID
End Sub