Real Software Forums

Hello,

I have this code in the open event of Canvas1:

#If TargetWin32 then //Windows only
Me.DoubleBuffer = True
Me.EraseBackground = False

#else //Linux and Macintosh

#endif

and when I scroll I still see the background being erased and get flickering.

How can I fix that?

Thanks.

Lennox.

How are you scrolling?

This is the code in ScrollBar1

In the ScrollBar1.ValueChanged event:
#If TargetWin32 then //Windows only
Canvas1.DoubleBuffer = True
Canvas1.EraseBackground = False

#else //Linux and Macintosh

#endif

Canvas1.Refresh



In the ScrollBar1ScrollBar1.Open event:
ScrollBar1.Maximum = Max(Canvas1.Height - self.Height, 0)
ScrollBar1.Value = Min(ScrollBar1.Value, ScrollBar1.Maximum)


Lennox

Canvas.Refresh defaults to EraseBackground = True. That is causing your flicker. Call it as

Thanks timhare,
I did that but no improvements.
Lennox

What are you scrolling? Are you drawing an image in Paint? Do you have controls sitting on the canvas? I don't see you calling canvas.scroll. Are you drawing offset by scrollbar.value? We need more information.

If you have a big picture and a small canvas:
You want to scroll the picture around so that you see part of it through the canvas.

Set the canvas erasebackground = false in design time. Doesnt matter if it is set on the Mac too.
I dont think doublebuffer makes much difference

In the scrollbar valuechanged event, use canvas1.invalidate false

Set hscroll maximum to picture.width - canvas.width
set vscroll maximum to picture.height - canvas.height

In the canvas paint event,

g.drawpicture bigpicture,0,0,canvas.width,canvas.height,hscroll1.value *-1,vscroll1.value *-1


Do NOT set the .background of the canvas in code as that causes a flash no matter what settings you use.

Thanks timhare and kermit and sorry about me not being specific.

I have controls sitting on the canvas and I am drawing offset by scrollbar.value.

Lennox

If you have controls on the canvas, you will have flicker.

that should be fixed long time ago.. is there still a feedback report for this?
If so, let's all add +1 to it..

I can get up to no other dev env wich has the same problem on windows...(yet)

OK thanks, flicker cannot be avoided on scrolling because of the canvas redrawing process I figure.

I have several bevelButtons on the canvas and if I mouse-over them fast they become invisible and then visible again, I have no code in their MouseEnter or MouseExit events. What is causing that and how can that be fixed.

Thanks.

Lennox

drawinto should get the job done

Thanks pawn,
I checked drawinto in the LR and got this

RectControl.DrawInto
Method
RectControl.DrawInto ( g as Graphics,x as Integer, y as Integer )
Draws the contents of the RectControl into the specified Graphics context. The parameters x and y are the coordinates of the top, left corner.

I am using this in Canvas1 Paint event:
Bevelbutton1.Top = 100 - ScrollBar1.value
Bevelbutton2.Top = 150 - ScrollBar1.value
Bevelbutton3.Top = 200 - ScrollBar1.value
Bevelbutton4.Top = 250 - ScrollBar1.value
.
.
.

How do I use Drawinto with those parameters?

Thanks.

Lennox

Actually i'm not sure if it'll help with the way you're doing it

But with what you have its probably worth attempting at least,

Bevelbutton1.DrawInto(g,Bevelbutton1.left,Bevelbutton1.top)
Bevelbutton2.DrawInto(g,Bevelbutton2.left,Bevelbutton2.top)
Bevelbutton3.DrawInto(g,Bevelbutton3.left,Bevelbutton3.top)
Bevelbutton4.DrawInto(g,Bevelbutton4.left,Bevelbutton4.top)

I always do this for windows:



when refreshing a canvas use (on windows):