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#20 Lens magnification problem when intersecting view boundary

zvtm (49)

As shown in attached screenshot (lensRenderingBug.png), the lens
incorrectly renders part of the magnified content when all of the following
conditions are met:
- the lens is only partially visible, crossing the view's boundary
- less than half of the lens is visible in the view

The amount of pixels incorrectly rendered is directly related to the
maximum magnification factor.

The problem comes from the fact that the pixels that should be rendered
in this region are outside of the area actually rendered (offscreen) by the
view and are never defined.

The way to fix this would be to make the offscreen rendering slightly
bigger than what is actually shown in the view, so that pixels that are not
visible without lenses but that might be visible when the lens intersects
the view boundary get painted before being translated to the visible
region of the screen by the lens.


  • Emmanuel Pietriga

  • Emmanuel Pietriga

    Logged In: YES

    The behaviour of this bug has changed with the new double-buffer
    implementation of lenses, but it still exists: the magnified content seen through
    a lens suffers from an offset when the lens is not fully within the view.

  • Emmanuel Pietriga

    Fixed in SVN on 20140619. Will be in release 0.11.2

  • Emmanuel Pietriga

    • status: open --> closed
    • Group: --> None


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