Not using negative sizes in wxBoxSizer breaks AUI layout

[hartwigw]

Assume the following code:

wxBoxSizer boxSizerPtr(new wxBoxSizer(wxHORIZONTAL));

boxSizerPtr->Add(firstWindow,0,0,0);
boxSizerPtr->AddStretchSpacer();
boxSizerPtr->Add(secondWindow,0,0,0);

this->SetSizer(boxSizerPtr);
...
Now, if the surrounding window's horizontal size is smaller than the size of its children, namely

this->GetSize().GetWidth() < firstWindow.GetSize().GetWidth()+secondWindow.GetSize().GetWidth()

than inside the box sizer's calculation method the stretch spacer's size becomes negative (at least temporarily). The width of the stretch spacer is adjusted later to zero but the remaining calculation is done with the previously calculated negative size.

Hartwig

Patch:

--- sizer_old.cpp 2008-05-08 09:02:13.000000000 +0200
+++ sizer_new.cpp 2008-09-28 10:03:12.000000000 +0200
@@ -1750,7 +1750,7 @@

item->SetDimension( child_pos, child_size );

- pt.y += height;
+ pt.y += item->GetSize().GetHeight();

}
else
{

@@ -1788,7 +1788,7 @@

item->SetDimension( child_pos, child_size );

- pt.x += width;
+ pt.x += item->GetSize().GetWidth();

}

}

[vadz]

I think it's wrong to use negative delta at all in this code so I've solved it differently in r56010. Please let me know if you have any problems with this fix, thanks!

[jjn]

This fix breaks the layout system of wxAUI.
Run auidemo and drag the vertical toolbar to the bottom. (screenshot attached)

[vadz]

The change still looks correct to me but it did indeed break wxAUI layout (interestingly enough, in different ways under MSW and GTK: under MSW the neighbouring pane keeps its size but starts encroaching on the status bar while under GTK it is resized when the toolbar is moved).

I can't find the problem myself but it seems that it is due to calling SetMinSize() with too big values somewhere, apparently because the code doesn't take into the account the fact that the toolbar size is smaller now that it doesn't show some buttons.

Ben, I'd be grateful for any help with this one because I am just too lost in wxAUI code. And I don't want to revert r56010 because it really seems like the correct thing to do.

TIA!

[jjn]

The problem occurs in the vertical direction only. When you drag a horizontal toolbar to the right, the minimum width also exceeds the real one, but nothing happens. Therefore SetMinSize() might be not a real problem.

I think it is hard to fix the AUI layout algorithm, even if Ben is not busy :) Alternatively don't you add something like the flag that allows negative delta to wxBoxSizer?

[vadz]

Thanks for this observation, it's indeed an argument against my theory. But now I'm even more puzzled as I don't understand where does this difference between vertical and horizontal directions come from.

As for the special flag: this would be awfully ugly. It really shouldn't be needed and I hope this can be fixed before the official 2.9.0 release to avoid the need for it.