Section 14 Extending the drawing Application

By using an alternate event when a line is drawn, we can achieve a better result. The MouseMove event can be used to draw curves with the same code as before. PicDraw1.Line ­(X,Y). This event has the facility to determine which mouse button is pressed when the mouse is being moved, so we can make it draw only when a mouse button is held down. The code is simple as … If Button = 1 then (draw the line).

This still has the problem in that the line starts from the top corner (0,0) and it would be good if it would start from where we want it. The properties CurrentX and CurrentY can be set with a MouseDown event. Thus the line can start and end where we like.

The code segment is as follows.

PicDraw1.CurrentX = X

PicDraw1.CurrrentY = Y

Planning

This program has only two objects. A command button to clear the picture and a picture. The picture is drawn by moving the mouse.

Code

Private Sub CmdClear_Click()

PicDraw.Cls

End Sub

Private Sub PicDraw_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)

PicDraw.CurrentX = X ' sets the starting position of line
PicDraw.CurrentY = Y

End Sub

Private Sub PicDraw_MouseMove(Button As Integer,Shift As Integer, X As Single, Y As Single)

If Button = 1 Then 

PicDraw.Line -(X, Y) ' draw a line to (x,y)

End If

End Sub 

Problems 14

1. Add a colour palette of at least 4 colours that would allow you to draw in different coloured lines.
2. Add a facility that would allow you to fill different areas with different colours.
3. Add a facility to draw different shapes.

Hint - circles can be drawn using the following.

General

Dim Xstart As Single
Dim Ystart As Single

Private Sub PicDraw_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)

PicDraw.Circle (Xstart, Ystart), Sqr((X - Xstart) ^ 2 + (Y - Ystart) ^ 2) ' Get the radius using Pythagoras

End Sub

Private Sub PicDraw_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)

Xstart = X
Ystart = Y

End Sub

Author: Mike Leishman

Created : June 28 1998