Mac: draw background into hole between scroll bars

[itsayellow]

Originally reported by Matthew Clapp (Bitbucket: itsayellow, GitHub: itsayellow)

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• Bitbucket: https://bitbucket.org/itsayellow/marcam/issue/20

[itsayellow]

Original comment by Matthew Clapp (Bitbucket: itsayellow, GitHub: itsayellow)

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difficult to consistently reproduce (at least on MacAir Yosemite)

[itsayellow]

Original comment by Matthew Clapp (Bitbucket: itsayellow, GitHub: itsayellow)

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Hard to reproduce this now.

[itsayellow]

To reproduce:

• Start with an image zoom and window size so that only one scrollbar is visible. The image should only be slightly larger than the window so that the scrollbar fills almost the whole scroll area.
• Zoom in one tick so that both scrollbars are visible. (Making lower-right corner not painted)

This should leave a chunk of the original scroll bar in the lower-right corner on Mac.

[itsayellow]

Possible fix (hack?)

For Zoom In operation:

• Check if only one scrollbar is visible
  • If True, then shrink canvas smaller than window, THEN enlarge to final size
  • This should first erase any scrollbar from window, then repaint both.

[itsayellow]

If above works only need to modify image_scrolled_canvas: set_virt_size_with_min

[itsayellow]

Or possibly,

1. Set virtual size to client area size (window size)
2. Draw a rectangle into lower-right corner of color wx.Window.GetBackgroundColor()
3. Set virtual size to proper size.

[itsayellow]

wx.Window.HasScrollbar(self, orient)