[DUG] Updating a property's memory address doesn't cause a redraw

[Paul Lyons]

Hi there

I've written a generalised interpolator that gradually changes the 
value of a property such as panel1.width from startValue to endValue 
over a given period. This gives me a general way of animating 
movements and positions of interface components.

I tell the interpolator the address of the property, the start and 
finish values:

interpolater.addProperty(addr(panel1.width), panel1.width, panel1.width+100);

As you can see, the property is passed as a pointer. The interpolator 
goes into a loop for whatever time duration I've specified, updating 
the property pro rata on each iteration. However, although the memory 
location where the property is stored does genuinely get updated, it 
seems that Delphi isn't aware that updating that memory location 
should generate a redraw event for the panel. I can force a redraw by 
putting a pair of net-null-effect statements like this

             panel1.width := panel1.width - 1;

             panel1.width := panel1.width + 1;

into the loop, and then the interpolation works fine, but the goal 
was to avoid having to tell interpolator anything about the component 
that needs to be redrawn other than the memory location of its property.

Things that don't work include

             application.processmessages

             panel1.update

             panel1.repaint

             panel1.invalidate

             panel1.width := panel1.width

Optimisation is not turned on.

It seems as though even if you force Delphi to redraw a component, it 
won't check the property values unless it knows that at least one 
property has been updated. So the problem is, having updated a memory 
location, how do I tell the component that its property has been updated?

Thanks
Paul