Pcbnew: Flipping board view doesn't flip layer order

[Reece Pollack]

When viewing a "flipped" board (i.e. viewed from the bottom), the layers are still ordered as if viewed from the top unless a bottom layer is selected. This is a problem when an inner layer contains a copper plane, as the components on the bottom are not visible when working with another inner layer.

For example, create a 4-layer board with a plane on one of the inner layers. Place components on both top and bottom, then flip the board in the View menu. Unless a bottom layer is selected the components on the bottom are invisible even though they are on the side being viewed, while components on the top are still visible through the plane. Selecting the bottom copper layer causes the bottom component to be visible but disappears again if another layer is selected, such as when a via to another layer is placed.

Another example of this without requiring filled inner layers is that top pads overlay bottom pads if a neutral layer like Edge.Cuts is selected.

While this can be worked around by displaying planes in outline mode or making them somewhat transparent, it makes more sense for the layers to be stacked in reverse order when viewing a flipped board.

Built from sources from a private branch derived from this Git commit:
    8a70acb Update demos to use V5 libraries.

Application: kicad
Version: (5.0.0-rc2-dev-688-g5f3e362), debug build
Libraries:
    wxWidgets 3.0.2
    libcurl/7.47.0 GnuTLS/3.4.10 zlib/1.2.8 libidn/1.32 librtmp/2.3
Platform: Linux 4.13.0-38-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.2 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
    Boost: 1.58.0
    Curl: 7.47.0
    Compiler: GCC 5.4.0 with C++ ABI 1009

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_ACTION_MENU=OFF
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_SPICE=ON

[Jeff Young (jeyjey)]

See also comments in duplicate.

[KiCad Janitor (kicad-janitor)]

KiCad bug tracker has moved to Gitlab. This report is now available here: https://gitlab.com/kicad/code/kicad/-/issues/2137