Contributor - Graphics 2D zoom + pixel_drawing_mode transparency

The 5.4.0 release of Scilab has brought new graphical features, but as well some regressions. Fixing them would be useful. Here are main ones:

2D zoom

2D zoom on multiple subplot axes

• When a figure has several 2D axes in column,
  • it was possible to draw a selection box covering multiples axes, and to simultaneously zoom them within the same selected "range". It was very handy, but this is no longer possible in Scilab.
  • Above all, the selection box could be defined from points laying outside axes viewports. It was very convenient to not loose any part near the viewport bounds. Restoring this feature would increase usability of the 2D zoom.

  • See the report #11959.

2D zoom with overlaying axes

When there are several superimposed axes (typically with different y-scales), the zoom no longer processes all axes, but just the first one on the top layer. To see the issue, run the Graphics => 2D plot => plotyy demo, and try to zoom on the data: the red curve is zoomed, but not the black one (that sets the x-scale). See the report #12110

Pseudo-transparency with gcf().pixel_drawing_mode="and"

The gcf().pixel_drawing_mode property enabling to emulate some transparency is out of work. See the report #12017 and the illustration there. Since adding a transparency alpha channel to Scilab graphics won't be done soon and easily, at least recovering the former .pixel_drawing_mode action shall be a priority.

Puzzled facets in 3D plot

Another major regression since Scilab 5.0 has never been fixed and still heavily penalize Scilab when rendering 3D facets. So almost any 3D object can be altered. The bad rendering is ocuring in particular when zooming 3D objects. It is reported as bug #8310. An illustration is available there