On Jul 7, 2006, at 8:24 AM, Chuck Pelto wrote:
Greetings All,
Could anyone point me at an example of how to make a canvas
interactive so that a user can click and/or drag to resize and
relocate a canvas object inside of a window?
Sure. Define a Canvas subclass called DraggableCanvas. Add private
properties
MouseDragX as Integer
MouseDragY as Integer.
Then implement the following two event handlers.
Function MouseDown(X As Integer, Y As Integer) As Boolean
me.MouseDragX = me.Window.MouseX
me.MouseDragY = me.Window.MouseY
Return true
End Function
Sub MouseDrag(X As Integer, Y As Integer)
If me.MouseDragX <> me.Window.MouseX or me.MouseDragY <>
me.Window.MouseY then
me.Left = me.Left + (me.Window.MouseX - me.MouseDragX)
me.Top = me.Top + (me.Window.MouseY - me.MouseDragY)
me.MouseDragX = me.Window.MouseX
me.MouseDragY = me.Window.MouseY
End if
End Sub
Now drop a DraggableCanvas onto a window. Implement its Paint event
handler so that you can see the thing.
Sub Paint(g As Graphics)
g.ForeColor = &cffffff
g.FillRect 0, 0, g.Width, g.Height
End Sub
Run the project and drag the Canvas around until you become bored.
Implementing a resizable canvas is more work, though not otherwise
difficult (once you know how, of course). In the next two issues of
RBD I will have articles that describe how to implement a simple
visual layout editor in which you can add, remove, resize and
relocate widgets on a canvas.
Charles Yeomans
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