Draw on a component with canvas
lazarus / 39-Graphics

----------------------------------------------------------------------
mmxngg · 2012-02-15 09:53

I want to draw a rectangle on a component (a scrollbox) for
dinamically select (at runtime) other components inside it.

I have tried this :

Code: [Select]{ Save the canvas }
DesignBuffer := TBitmap.Create;
DesignBuffer.LoadFromDevice(ScrollBoxDesign.Canvas.Handle);
DesignArea.Top    := ScrollBoxDesign.VertScrollBar.Position;
DesignArea.Bottom := DesignArea.Top  + ScrollBoxDesign.Height - 1;
DesignArea.Left   := ScrollBoxDesign.HorzScrollBar.Position;
DesignArea.Right  := DesignArea.Left + ScrollBoxDesign.Width  - 1;

{ Draw something (Selection are inside bounds) }
ScrollBoxDesign.Canvas.Rectangle(SelectionLeft, SelectionTop,
SelectionRight, SelectionBottom);

{ Restore the canvas }
ScrollBoxDesign.Canvas.CopyRect(DesignArea, DesignBuffer.Canvas,
DesignArea);
Works well when scrollbox don't have scrolling else i get SIGSEGV
error when i try to restore the canvas. What's wrong ?

----------------------------------------------------------------------
User137 · 2012-02-15 11:17

How is DesignBuffer handled? You are creating new instance of TBitmap
every time you save, are you freeing it properly after it is used to
restore?

----------------------------------------------------------------------
mmxngg · 2012-02-15 18:32

OnMouseDown - Create and save
OnMouseMove - Restore and draw
OnMouseUp - Restore and free

All my issues are with TScrollbox....i will cut off it and replaced by
custom component for making a scroll... :/